Recent Seeding missions

September 2009

The pattern finally changed during the month of September and this allowed much needed rain to fall across most portions of the target area.  After looking at the observed precipitation map below for the month, it seems that the northern and southern most extremes of the target area saw the most precipitation.  However, most areas were above normal for the month with the wet spots being central Webb County and southern/northern Uvalde County.  Weather modification wise, flight activity picked up greatly from what it had been in July but was about average for this time of year.  A total of 10 seeding flights took place on 8 seeding days, with 3 reconnaissance flights as well.  All of these missions were classified as rain enhancement and a total of 119 flares and 4,720g of AgI was dispensed during the month of September.

 Below is a spreadsheet for flight activity for the month. Below is a spreadsheet for flight activity for the month.

Click here to view September 2009 flight activity

September 2009 Precipitation Map

September 1

An upper level trough was located just to the east of the area with a strong jetstreak moving over the area this afternoon.  This combined with peak heating and good moisture gave way to convection during the afternoon hours.  Convection began to occur over LaSalle and Dimmit counties during the early afternoon hours.  Convection got off to a slow start in this area and never really blossomed into anything more than a few cells.  Meanwhile, to the south of Webb County convection was slowly moving in.  The first flight occurred in LaSalle and Dimmit counties and the second flight was launched on convection in Webb County, but better convection popped up as soon as the pilot was launched in LaSalle County.   The convection south of Webb County started to dissipate as soon as it got close to the target area border.  Convection was seeded in LaSalle County and another small cluster of cells popped up in Uvalde County.  Initially the convection was not very strong and lacked bases, but upon further investigation, the pilot was able to seed these cells.

September 4

A trough of low pressure was located over New Mexico into west Texas.  A shortwave moved through during the evening hours making the flow a bit more diffluent over the area.  This combined with residual boundaries from convection yesterday and a very buoyant atmosphere gave rise to convection during early evening hours.  A thick shield of cirrus was noted throughout most of the day which delayed the onset of convection.  However, when a shortwave moved in south Texas from Mexico, convection began to form in LaSalle, Dimmit, and Webb counties.  A flight was launched on this convection and the pilot was able to find good inflow with most of the convection forming in the target area.  Most all of the convection was seeded but the pilot finally needed to land as ceilings were becoming an issue near the end of the mission.

 September 5

A weak low was located to the northwest of the area.  As well, moisture was being brought in from the Pacific at the mid and upper levels from the remnants of a tropical storm.  As well, a good southeasterly flow was coming from the Gulf of Mexico in the lower levels.  Lift from the low and daytime heating gave way to very tropical like convection today.  Showers and thunderstorms began to form during the afternoon hours as daytime heating got going.  The convection started in LaSalle and Webb counties and a seeding flight occurred.  During the flight, the pilot found good inflow and a very prominent shelf along the convection.  As he went further to the west/southwest, bases were increasingly hard to find and was unable to see the southwestern part of the line of convection.  Convection occurred in other parts of the target are today, but with the majority of the mass of the cloud below 4 km, seeding was not conducted due to the non effect nature of glaciogenic seeding on this warm convection.

September 6

Very weak showers started to occur in Uvalde County during the early afternoon hours.  A flight was launched on this activity but seeing that the atmosphere was very tropical in nature, no seeding was done in Uvalde County.  This tropical atmosphere was characterized by very warm convection with low cloud tops.  Convection become very unorganized and soon after launching there was no storm structure was evident.

September 7

A mid to upper level trough was located across the southern Plains and Texas.  As well, during the afternoon hours a shortwave moved into the area from northern Mexico along the base of the trough.  This trough and associated shortwave combined with ample moisture and daytime heating lead to convection today.  Another day of very high precipitable water values yielded very weak convection starting during the afternoon hours.  By the mid afternoon hour, convection seemed to maybe be becoming a little bit more intense and taller cloud in Zavala and Frio counties.  The pilot took awhile to find inflow and when it was found; it was weak and only in small area.  As well the pilot reported very unorganized, broken bases.  The pilot continued to investigate this area, but was having no luck find inflow with the storms around the central target area.

September 9

A mid to upper level trough was located across the southern Plains and Texas.  As well, during the afternoon hours a shortwave moved into the area from northern Mexico along the base of the trough.  This trough and associated shortwave combined with ample moisture and daytime heating to lead to convection today.  As well during the evening hours, convection moved in from west Texas.   Weak convection started to form in Uvalde County during the early afternoon hours.  Most of the cloud mass was generally below 4 km but this eventually changed with   convection in Uvalde County and a pilot was launched.  Upon encounter, the pilot reported some good bases but most that were found were unorganized and inflow was hard to find.  On the eastern side of the area of thunderstorms is where the majority of the inflow was found as the west side yielded mostly rain and no bases.  This was sufficiently seeded and the pilot returned to base.  As well, weak convection was starting to work into the area from Mexico in Webb County and this was monitored for the possibility of another flight.  The convection in Uvalde County continued to propagate into Zavala County and seemed to be aided by an outflow boundary there.  Another flight was launched to seed this area of convection a second time.  The pilot was able to do some seeding but there was an increasing downtrend in reflectivity and bases.  Additionally convection occurred during the afternoon hours in the target area but most of it was warm rain process and no lighting was being reported with it.  One last flight was done today as convection moved into the western side of the target area from west Texas. Convection first entered northwestern Uvalde County, but a flash flood warning was issued for this section of the line of convection.  Convection soon moved into western Zavala and Dimmit counties which was not warned on. This convection seemed to have more depth than most of the convection seeded earlier in the day and lightning was frequent with this convection.  The last flight was concluded early to deteriorating visibility.

September 19

Convection quickly fired on the southwestern border of Webb County as a weak shortwave moved into Texas from northern Mexico.  Most convection remained in Mexico for some time but when it crossed the border it was located over Laredo which was unable to be flown on.  As the convection continued to moved to the east, it became embedded in light rain.  A pilot was launched on this convection but upon encounter, was unable to get to stronger cells due to the embedded nature of the convection.

September 22

A very potent vertically stacked low was located over the central Plains.  This put Texas on the southeastern side of the low and as disturbances moved along the base of the low, this triggered convection over the area.  The convection for this flight was due to a cold front moving into south Texas.  The front combined with a very good mid level flow from the Pacific and good low level flow off the Gulf lead to a line of convection during the early morning hours.  A broken line of convection was located just north of the target area around 12Z.  Convection before it entered the target area was not that promising but when convection moved into Uvalde County, it was of seeedable strength and depth.  A pilot was launched on this due to the fact that clear conditions were available during takeoff.  As the pilot reached the convection, ceilings lowered substantially and he was unable to get to the main convection located in northeastern Uvalde County.  However, the pilot found a row of new development, probably along the outflow boundary, in Uvalde and Medina counties.  The STWMA pilots were unable to take off due to low ceilings, so seeding was done for them during this mission.  The pilot found a line of good inflow along these developing turrets and seeding was done.  After most of the new development was investigated, the pilot returned to base as ceilings were becoming an issue.

September 28

A late night mission occurred over Uvalde County as a weak cold front was moving through the target area.  This combined with a weak shortwave allowed for convection to explode over Uvalde County.  A seeding flight was conducted  on this convection and the pilot reported frequent lightning with the convection that was seeded.  Seeding operations were concluded as all the convection in the target area has been sufficiently seeded.

September 29

Convection started to develop in Webb and LaSalle counties during the early morning hours as the cold front that caused convection late last night, continued its movement to the south.  This weak boundary encountered very moist and unstable air as it moved into the southern target area.  A flight was launched on this convection but upon encounter, the pilot was unable to be seeded due to the total lack of bases associated with the convection and no inflow.  Soon after the flight concluded, flash flood warnings were issued for Webb County, thus ending any hope another flight with that area of convection.  Later into the afternoon, more convection fired in LaSalle and Dimmit counties.  This convection was much better organized, with good bases and inflow that the pilot was able to find.  Seeding was concluded as this convection had been given the proper dose due to its size.

August 2009

August proved to be yet another dry month for the target area and most of south Texas.  Almost the entire target area was below normal precipitation wise, with the majority of the area about 3 to 4 inches below normal.  Some locations faired better than others  and were confined to the southern parts of the target area.  Portions of east/southeastern Webb County were actually 1 to 2 inches below.  This can be explain by the typical pattern for the month which yielded high pressure over all of south Texas except for the lower Rio Grande Plains, where coastal convection was allowed to move inland with a weakness in the high there.  August  yielded fewer flights than July, with  lower flight hours and silver iodide usage. One anomaly was a hail suppression flight near the end of the month that occurred in Webb County.  For the month of August, a total of 130 AgI flares and 5,200g of AgI were used. 

 Below is a spreadsheet for flight activity for the month.

Click here to view August 2009 flight activity

August 2009 Precipitation Map

August 12

A shortwave moving across central Texas gave rise to convection over that part of the state during the afternoon hours.  This convection put off a well organized outflow boundary that spawned new showers and thunderstorms along the Texas Hill County and into the target area. Convection began to move into the northern target, a seeding flight was launched on it.  The convection as first seemed rather to have good intensity and good cloud tops.  As the convection moved into the target area, it seemed to go downhill in a hurry.  By the time the pilot actually reached the convection, undefined bases, weak convection and minimal inflow was present.  Meanwhile, it put out an outflow boundary that moved through the target area.  This helps to make way for convection as it reached the central parts of the target area when peak heating was occurring.  Another seeding flight was launched on a cell in southeastern Dimmit County. 

August 13

High pressure over west Texas shifted a bit further to the east than yesterday.  This allowed more moisture to work into the eastern/southeastern parts of the target area.  As well, another outflow boundary moved in from the north into southwest Texas.  The seabreeze was able to move further than it usually does into the southern parts of the target area during the afternoon.  Convection was located at both extremes of the target area today.  In the northern target area, convection was initiating along a southward propagating outflow boundary.  In the southern target area, the seabreeze was causing convection in Webb and LaSalle counties.  Convection to the north was marginal at best and the pilot worked hard to find inflow.  Only two flares were fired during this mission as the flare racks failed to allow flares to be fired when inflow was actually found.  Convection was best in the southern target area today and a plane was launched to seed it there.  Convection was robust and provided good inflow.  Convection began to work into the target area from Duval and the STWMA target area during the last half of the mission.  Convection that was seeded in eastern LaSalle was seeded for the second time after being seeded by STWMA in McMullen County.  This convection continued its movement to the west and the seeding flight was terminated due to all the convection in the target area being seeded.

August 18

Upper level high located over the western Gulf of Mexico and upper level trough across the Southwestern U.S into the northern Plains.   The seabreeze boundary moved into the area late during the day and this gave rise to convection in the target area.  Convection initiated along the seabreeze today and eventually worked its way into Webb County.  Convection seemed pretty marginal through most of the afternoon but exploded a bit when it entered the target area.  A pilot was launched on this convection but convection did not last very long when seeding and after seeding was done.  The pilot returned to base but did find a developing cumulus cloud that was painting weak reflectivity on TITAN.  This cloud was seeded then the pilot returned to base.

August 27

A weak trough axis existed to the east of the area.  As a result, disturbances were being allowed to move down from north Texas into west Texas.  These disturbances were putting out outflow boundaries that propagated into the western Hill County during the afternoon hours giving rise to convection.  Convection was moving into the target area from the north and northwest during the afternoon hours.  KDFX was not opertional for the entire mission but using surrounding radars allows the flight to continue.   During the mission, the pilot only reported a small number of clouds the contained workable bases and inflow was only confined to a small area.  Convection was seeding in northern Uvalde County on this flight.

August 28

A weak trough axis existed was still to the east of the area, but was further west than yesterday.  As well at the surface, a weak frontal boundary was located just north of the area.  Moisture combined with daytime heating and the weak boundary led to convection today.  Convection began to first form in the northern parts of Uvalde County.  As the afternoon went on, convection began to form in the southern parts of the target area as well.  However the best convection, in regards to inflow and bases, was located in Uvalde and Zavala counties.  A pilot was launched on convection in northern Uvalde County and eventually flew down to Webb County were additional convection was occurring. Convection in Uvalde County only produced weak inflow and was hard to find.  The convection in Webb and LaSalle counties was better but still somewhat difficult to find inflow. Convection began to form along an outflow boundary in Zavala County, therefore another flight was launched.  Convection seeded in Zavala County was by far the best in regards to inflow and bases.  Into the evening hours, convection exploded across the southern target area and eventually formed into an MCS that covered most of Dimmit, LaSalle, and Webb counties.  The second flight landed due to being almost out of fuel and out of flares.  As well, radar showed it increasingly hard to find inflow and bases without rain due to the formation of the MCS.

August 30

A weak trough axis existed was still to the east of the area, but was further west than yesterday.  As well at the surface, a weak frontal boundary was located over the southern target area, mainly Webb County.  This boundary separated very moist air from much drier air to the north.  Most of Webb County resided on the south side of this boundary and thus very moist air was in place.  As daytime heating got going, convection started to form in an east/west oriented line across the county.  Convection started off weak early in the afternoon in Webb County but quickly became stronger.  A pilot was launched on this convection and upon encounter, found very good inflow and good bases.  Shortly after seeding began, convection became severe and hail suppression was conducted in Webb County.  Throughout the flight, the pilot reported good rain shafts and plentiful inflow.  Seeding was finished when enough material had been put into the cloud.

July 2009

July proved to be another extremely dry month across the target area.  Most locations in the target area were below normal this month but for the first time in 2009, some locations were actually above normal for the month.  Parts of central and eastern Zavala counties were above normal, mostly due to a couple of strong rainfall events near the end of the month.  As well locations in south/southeastern Uvalde County were slightly above normal for the month.  Locations in the central target area were right around normal, with locations in the southern target area including Dimmit, LaSalle, and Webb being 1 to 2 inches below normal for the month.  Weather modification wise, operations were slightly below normal for the month, but a good amount of cloud seeding did occur during the month.  Most of the counties in the target area saw convection as the weather pattern allowed for weather systems to come from both the north and south at a time of the year when convection usually just comes from the south.  For the month of July, a total of 231 flares and 9.240g of AgI were used.  Below is a spreadsheet for flight activity for the month.

Click here to view July 2009 flight activity

July 2009 Precipitation Map

July 2

Upper level high located over west Texas/northern Mexico with upper level ridge across most of the central and western parts of the U.S. A mid level high was a bit further to the east than its upper level reflection.  In the lower levels, high moisture values existed mostly along coastal areas and further into the lower Rio Grande Plains due to a weak tropical wave coming ashore near Brownsville. 

Conditions were favorable today for the seabreeze to move into the target area.  A large complex of showers and thunderstorms associated with a weak tropical wave only helped to enhance the seabreeze today.  A pilot was launched on convection that was moving in from the Coastal Plains.  However, as this convection moved into Webb County, it started to weaken considerably.  As well, the SWTREA meteorologist was working for the STWMA meteorologist, so after seeding was done in the SWTREA target area, the pilot moved over to the STWMA target area to help out.  Seeding was done in the STWMA area in Live Oak, McMullen, Frio, and Atascosa counties.  In the SWTREA target area, seeding was conducted in LaSalle and Webb counties.  Seeding that was done in LaSalle and Webb counties were not as good as convection that was closer to the coast.

July 6

Weak showers and thunderstorms began to form to the north and northwest of the target area during the late afternoon hours.  As time progressed, convection began to move into target area and new cells were forming as well.  A seeding flight took place in Uvalde County but the pilot was unable to find inflow with most of the cells early on.  The only cell that was able to be seeded that actually had bases was in northwestern Uvalde County.  As time went on, a line of thunderstorms formed from about the town of Uvalde to Hondo and further to the northeast.  Convection was again seeded and was located across southeastern Uvalde County and northeastern Zavala County.  The information for this flight can be found on the STWMA report as they did the seeding at this point.  As the convection continued to the south/southeast it did start to fall apart.  Meanwhile, further to the southeast, the seabreeze boundary has moved into eastern LaSalle and Webb counties.  Another seeding flight was launched.  The pilot did have a little luck with this convection but weak inflows plagued most of the flight.  Even more convection continued in Dimmit and Maverick counties but upon encounter, the storms were decreasing in intensity.  Seeding operations concluded when there were not any other cells around to seed.

July 7

Some weak convection developed earlier in the day in southeastern Webb County ahead of the seabreeze but upon encounter, the pilot reported that air was very dirty.  Upon encounter of convection, cells were very short-lived, no bases, and had very little vertical depth.  A bit later in the day and further to the northwest in the central target area, convection began to occur in Uvalde and Zavala counties.  As well, convection was occurring in northeastern Maverick County and was moving into northwestern Zavala County.  The pilot initially had problems finding inflow with the convection in Uvalde County, so the pilot continued into Zavala County where inflow was found with the convection there.  Seeding continued until the pilot ran out of flares.  Another plane was going to launch but was unable to do so due to mechanical problems.  However, over time, it seemed that most of the convection in the target area was seeded.

July 17

Convection began to form along the Hill County during the afternoon hours.  This convection slowly moved to the south/southwest and entered the target area along the northern edge.  A pilot was launched on this convection and was seeded until the pilot ran out of flares.   Meanwhile, another pilot was being readied to launch on the convection as it continued from Uvalde County in Zavala County.  The convection remained rather strong, so a second flight was launched on the convection to be seeded again.  The pilot on the second flight had trouble finding inflow and as the flight progressed, the convection began to weaken considerably.  The pilot was no longer able to find inflow and seeding concluded.

July 18

A mid level to upper level trough was located over the area which gave rise to the showers and thunderstorms over the northern portions of the target area.  However, the seedable convection today was due to an enhanced seabreeze moving into the southeastern target area.  Convection once again began to form along the northern end of the target area.  However, as the convection moved to the south, it dissipated rather quickly.  This occurred just as the convection was entering northern Uvalde County.  The convection was likely short lived due to the ample cirrus shield that was located over the northern parts of the target area from a dying MCS that moved close to the area earlier in the day.  However, the southern target area remained immune from this shield seeing that it was too far to the north and by the late afternoon to early evening hours, convection began to occur in southeastern Webb County along the seabreeze.  Convection along the seabreeze was seeded and the pilot reported that inflow was adequate for seeding and bases were good.  The pilot did report that cloud depth wasn’t as good as it usually was, as these cells really didn’t get that tall.

July 20

Mid to upper level high has moved even further to the west over the past couple of days.  This allowed a mid level trough to meander across Texas into the lower Mississippi River Valley.  This trough has allowed a weak stationary boundary to move back and forth across central Texas the past couple of days.  This boundary combined with daytime heating and a good moisture profile over the area allowed for convection today.  Convection across the Hill County that formed along a surface boundary as it has the past several days occurred once again today.  By the afternoon hours, this convection began to move to the south/southeast into the target area.  A pilot was launched on the convection as it moved into Uvalde County.  Near the beginning part of the mission, the pilot was having trouble finding inflow with the initial convection.  The pilot flew along the front of the leading edge of the convection and was not able to find inflow.  The pilot was instructed to return to base.  However, before he landed, another cell formed in southern Uvalde County that was further south of the initial convection. The pilot proceeded to the new cell and was able to find inflow with this cell and the subsequent cells the formed in northeastern Zavala County.  After these cells were seeded, not much else in the way of convection was in the target area, so the pilot returned to base.

July 30

An MCS moved just to the north of the area earlier this morning.  The convection associated with this MCS was expected to dissipate as the previous days’ MCS’s had.  But as the MCS continued to move to the south/southeast, it began to regenerate just to the north and northwest of the target area.  The leading edge of the MCS was seeded in northern Uvalde County.  The pilot continually reported good bases, good inflow, and frequent lighting throughout the mission.  As this convection moved south, an outflow boundary was produced and the convection “jumped” in front of the old leading edge, leaving the pilot behind the outflow boundary.  This convection further during the mission produced a very strong gust front and the pilot reported a large amount of dust being ingested by the convection.  Even with this, the convection continued to the south/southeast.  The pilot finally ended up moving through the gust front and working along the leading edge again.  The pilot before was able to find distinct areas of inflow associated with each particular cell.  However, when he was on in front of this gust front, he found inflow all along it, even when he was not near the cell.  The majority of the seeding took place behind the gust front but the last four flares were fired when the pilot was located on the southern side of the gust front.

July 31

A vorticity maxima was located across the Rio Grande.  This vorticity maxima combined with daytime heating and excellent moisture gave rise to convection today.   During the early afternoon hours, convection began to form near the river and into northwestern Webb County.  A few weak cells were developing in southern Maverick and southwestern Dimmit counties.  A seeding flight was launched on these cells and after a short while, an explosive development of showers and thunderstorms occurred in northern Webb County and western Dimmit County.  Seeding was done on these cells and along a line that stretched from northern Webb County into southern Uvalde County.  The pilot reported frequent lightning throughout the flight and very good inflow.  The line continued to move to the east/northeast and seeding operations were concluded when enough material had been put into the convection.

June 2009

June proved to be another hot and dry month for the target area and most of south Texas.  The rainfall table below shows just how dry it was, with most of the target area only seeing about 5-10% of there monthly average of precipitation.  As well, weather modification operations were below normal, but still at a decent number due to the aggressive nature of the project.  The months allowed for flights only at the beginning and end of the month.  In between these two period, a persistent ridge of high pressure remained over south Texas. The only locations that actually faired well were central Webb County and southeastern LaSalle.  This was indicative of how active the seabreeze was during the month of June.  For the month of June, a total of 155 flares and 6,200g of AgI were used.  Below is a spreadsheet for flight activity for the month.

Click here to view June 2009 flight activity

June 2009 Precipitation Map

June 1

Weak thunderstorms started to occur during the late afternoon hours across eastern Webb County. These showers were due to the seabreeze making its way into Webb County These showers were very isolated in nature, but one of the cells became very potent as a pilot was launched to it.  The pilot reported a very good shelf with this cloud and new growth on the northwestern side.  The pilot did most of his seeding here.  However, the cell quickly began to dissipate and the pilot was unable to find anymore inflow.  A reconnaissance flight was launched on a cell that formed in northeastern Dimmit/northwestern LaSalle County right before sunset. This cell was formed as the seasbreeze boundary moved inland.  During the progression of the evening, the seabreeze could be seen on radar all the way up to Uvalde and Kinney counties. The cell became very potent for 2-3 scans.  A pilot was launched on this cell but did not last long and upon encounter of it, the pilot was unable to find any inflow associated with the cell.  As well, the pilot reported that the tops on the northwest side were becoming less defined and was only able to find smooth air associated with this cell.

June 2

Convection in Val Verde County earlier in the day produced an outflow boundary that started to move in the northwestern target area around 0230Z.  As this outflow boundary moved into western Uvalde County, convection started to occur along it.  As well, an MCS was moving into the Hill County from north Texas.  Shower and thunderstorms formed along the western edge of the target area in Zavala and Uvalde County.  Convection further south of the main outflow boundary in Uvalde County did not fair very well, but the main line of convection in Uvalde County faired very well.  This is where the majority of the seeding took place and seeding was concluded as this line of convection moved out of the target area.  Throughout the mission, the pilot stated that the convection had excellent lightning associated with it and a large, pronounced shelf was evident.  The MCS that was moving into south Texas ended sliding to the east/southeast and did not impact the target area.

June 3

The MCS from the overnight hours left an outflow boundary located across the SWTREA target area.  During the afternoon hours, weak showers began to form in LaSalle and Zavala counties.  A flight investigated these showers, but they were not mature enough to conduct seeding on.  The pilot then flew back into the STWMA target area.  After a short amount of time, showers and thunderstorms began to increase in coverage and intensity in LaSalle and Dimmit counties.  Seeding was conducted here and a short while later, seeding was also conducted in Zavala County.  Inflow was somewhat hard to find to find today, probably most likely due to slow storm motions.  However, when it was found, inflow values were rather high especially with convection that formed near the tail end of the flight.  Eventually, convection merged together over the target area and extended from a Uvalde County to LaSalle County line as it moved to the south/southeast.

June 25

A CU field developed early over the western Hill county.  The bulk of the convection today developed in Bandera and Medina counties.  Convection moved from northeast to southwest and around 22Z, moved into Uvalde County.  A seeding flight was already taking place in the STWMA target area, so the plane came to Uvalde to investigate convection there. The first round of convection that moved into the northeastern corner of Uvalde County was investigated but no inflow was found with it.  Another round of convection developed over northern Uvalde County and the flight flew back to take a look at it.  This convection was weak and the pilot reported marginal bases and low cloud tops.  As well, when seeding was conducted, only weak inflows were reported.

June 30

Convection was forming along a boundary just to the north of the area during the early afternoon hours.  Convection started to move closer to the northern boundary of Uvalde County so a flight was launched.  Convection during this flight only moved into the extreme northern fringes of Uvalde County and was marginal.  A short while later, convection started to developed across the border from Webb County in Mexico.  As well, the outflow boundary that was north of the area earlier this afternoon finally started to make its way south.  This allowed an explosion of convection across northern Webb, southern Maverick and Dimmit counties.  Seeding was conducted on this convection and the pilot reported frequent lightning, good inflow, and very good bases.  After the complex of storms has received a proper dosage, the flight was terminated.  An hour after the second flight was concluded, convection began to re-fire over central Webb County due to lower CIN values and convergence occurring there.  Another flight was launched in response of this.  Inflow was somewhat difficult to find and when inflow was found it was weak and associated with light rain.  However, some seeding was able to occur.  The flight was concluded when a flash flood warning was issued for the convection being seeded.  A total of three flights were flown today in the target area.

May 2009

May turned out to be quite a busy month, however you wouldn't know if from the first two weeks of the month.  The first two weeks of the month were extremely dry and hot due to an unseasonably strong ridge of high pressure over the central U.S.  This type of synoptic pattern is more indicative of mid July rather than early May.  However, by mid month, the pattern shifted to a more favorable one over south Texas.  This pattern allowed for ample rainfall to occur, particularly over the southern and southeastern parts of the target area.  Most locations in Webb and LaSalle counties were able to come out above normal for the month, which can be seen in the precipitation map below.  Portions of Uvalde and Zavala saw the least amount of rainfall for the month for the target area as the table below clearly shows.  Weather modification wise, the last part of the month was very active compared to the slow start the first two months of the season. As well, a good amount of severe weather occurred, allowing for a number of hail suppression missions over the target area. A total of 364 flares and 14,560g of AgI were used this month.

Click here to view May 2009 flight activity

May 2009 Precipitation Map

May 15

Convection rapidly exploded across the entire target area during the early afternoon hours across the target area as a shortwave was lifting out of Mexico into a moist and unstable air mass.  Cells become rather large in a few scans.  Pilot was called and a seeding mission was launched on convection.  However, first pilot could not find inflow with strong cells over Uvalde, Dimmit, and Zavala counties.  Another pilot was launched and proceeded to nearest convection in southwestern Dimmit County.  The second pilot found inflow with convection in southwestern Dimmit County.  Severe weather statements were issues by the NWS but no T-storm warnings occurred.  Flood advisories were issues for the Dimmit and Zavala counties around 0245Z. 

May 16

Convection started to occur early in the morning over LaSalle and Webb.  A pilot was launched on this convection.  This was the first convection that fired during the day and as the day went on, convection began to occur in locations further to the north.  An outflow boundary/cold front was located over the Hill County and convection began to break out ahead of this boundary and along it.  Convection was seeded in LaSalle and Webb counties first then in Frio County for STWMA as convection began to initiate everywhere.  Cells in Zavala County where then seeded. The pilot tired to find inflow with storms in Uvalde County as well but visibility became a problem near the end and bases were almost to the ground.  This ended seeded over the area even though convection was still ongoing.  Overall, inflow was good during the duration of the flight and almost all convection was seeded or looked at.

May 22

A reconnaissance flight was launched on convection that was moving in the northwestern corner of Uvalde County. Upon encounter of the convection, the flares on the aircraft would not fire.  Additionally the convection seemed to be showing an overall weakening trend. 

May 23

During the latter half of the afternoon convection began to develop and move into both the northern and southern sections of the target area.  A flight was launched initially to investigate clouds in Uvalde County, but the plane was redirected to LaSalle County as the activity in Uvalde County was marginal at best and convection near Encinal appeared to be faring better on radar before seeding.  This activity was seeded, after which the plane returned to base.  Additional convection developed in Webb County after 8pm and another flight was launched to investigate and eventually seed this activity.  An MCS approached the Rio Grande and western sections of the target area after 10pm but much of this activity was embedded in a larger shield of light rain and was not seeded.  A total of three flights were conducted today due to the persistent and the widespread nature of convection.

May 24

Convection developed over the northern target area during the mid afternoon hours and gradually moved southward.  A flight was dispatched shortly after 3pm to investigate clouds over the EAA portion of the target area where the convection was concentrated.  Because there were several clouds close to each other, the randomization protocol could not be enacted and operational seeding commenced.  The plane also assisted with seeding in STWMA’s target area – Bandera and Medina counties.  With no other activity further south, seeding operations were concluded.

May 27

A quasi-stationary boundary existed across the Hill County.  As well, an outflow boundary was across the coast bend and made its way westward throughout the afternoon.  A very unstable airmass was in place with high dewpoint values and good daytime heating occurring in the late afternoon hours.  A weak upper level jetstreak moving out of Mexico also helped to fuel convection into the evening hours.  Convection first started to form to the east but as the afternoon went out, showers and thunderstorms started to build into the target area.  A pilot was launched on convection that was located in Edwards County near Rocksprings.  A very strong thunderstorm quickly became severe and was moving southeast into the target area.  Rain enhancement was preformed first and after a warning was issued, hail suppression was conducted    Pilot reported good lightning and strong inflow with the storm initially.  As the cell moved into the target area, more convection was forming along outflow boundaries from convection east of Uvalde County.  Another flight was launched and once again hail suppression was conducted.  Seeding ended with this cell as a Flash Flood Warning was issued for this particular cell.  However, strong to severe convection was seeded in Zavala County was well.  These cells were also seeded for hail suppression.  Seeding ended due to a Flash Flood warning and later a tornado warning being issued.  The pilot was not able to see the cell sufficiently before the warning was issued.  More convection was being monitored across the Rio Grande but low level steering did not allow these to enter the target area.  A total of two flights took place today in the target area.

May 29

The first seeding flight of May 29^th was launched on an MCS that started to approach the northern/northwestern edge of the target area shortly after midnight.  This MCS had been showing signs of weakening as it approached the target area but radar was still showing strong convection.  Seeding was done in northern Uvalde County and the pilot reported good inflow and frequent lightning. However, after some length of time, the pilot was having trouble finding inflow and as well radar showed weaker intensities occur as the MCS continue to the east/southeast.

Very weak showers and thunderstorms started off the day but as the day went on, explosive development of thunderstorms occurred as a shortwave moved across the area from Mexico. This shortwave was well timed with the peak of daytime heating and an unstable profile existed over the area.  A pilot was launched on weak convection forming in southeastern Zavala County.  Echoes were slow to show up but pilot reports of tall Cu’s and satellite imagery showing the same thing allowed seeding to take place.  Most of the seeding early on was conducted on clouds that were not producing any type of radar return.  However, as seeding continued, radar returns were showing up in these areas.  Seeding with the first flight was done mostly in Zavala County where the best Cu field existed.  However, storms begin to fire after this mission concluded in Uvalde County.  Another flight was launched on convection that began to fire in Uvalde County.  The convection in Uvalde was small in coverage but very intense.  This was seeded successfully.  Additionally, convection that has been moving east into Texas across the river finally started to work into western Webb County.  The pilot flew down to these storms as they entered the target area and was able to fire a couple of flares, but light rain was reported with the inflow and seeding was then terminated. 

May 30

Weak convection was developing in Uvalde County during the early evening hours.  A flight was launched into the northern county to see if convection was seeable.  The pilot reported that clouds were not developing vertically as they should be.  Convection continued there but the pilot was unable to find inflow with the weak convection.

May 31

Convection was moving into the target area from the east in Mexico.  As this convection moved closed to the border, small cells began to form in front of it.  As these cells entered the target area, where strong instability had existed all day, a rapid intensification occurred.  In addition, a strong shortwave was moving out of Mexico into the Rio Grande Plains which helped to further help convection across the border and help with intensification.   A pilot was already in route when this began to occur in western Dimmit and Zavala counties. Due to the severity of the storms, hail suppression operations were conducted.  These storms rapidly become severe as they worked their way across the western side of the target area. Gradually, the individual cells merged and formed a line of convection that extended from La Pryor south to northern Webb County.  Seeding was  conducted along the northern side of the line, from Crystal City to about Carrizo Springs.  However, when the pilot tired to move further south of Carrizo Springs, light rain was occurring ahead of the main line of convection.  Many attempts were made to seed the convection, but the lack of inflow and an abundance of rain out ahead of this line of convection inhibited it.  As well, seeding could not continue further to the east or south due to a flash flood warning that had been issued for LaSalle and Webb counties.

April 2009

A very dismal seeding period occurred during the month of April.  This month was below normal for weather modification standards. Usually in April, the severe weather season in south Texas is coming into full swing, with a peak occurring in May. However, due to a continuing synoptic pattern unfavorable for thunderstorm development, only two flights occurred during the month, one of which was a reconnaissance flight.  The other flight was classified as a hail suppression flight.  A total of 53 flares and 2,120g of AgI was used during the month of April.  The entire target area was below normal precipitation wise with the exception of northeastern LaSalle County, which can be seen in the precipitation map below.  As well, flight activity was below normal. These rainfall totals show an increase from month, but still very far below normal for this time of year.

Click here to view April 2009 flight activity

April 2009 Precipitation Map

April 17

A mid to upper level shortwave/jetstreak was moving across the target area at the time of when convection was occurring.  The two dynamics combined with a good moisture convergence and high cape values to help with convective imitation.  Convection that had been south of Webb County in Zapata County had finally started to move into the southern part of Webb County during the evening hours.  Ceilings were originally thought to be a problem but upon watching surface observations, ceilings would allow for a seeding flight.  Inflow throughout the mission was not as intense as one would expect with a storm of this intensity but none the less seeding operations were conducted.  Hail suppression was conducted due to the possible presence of hail with the storm and the issuing of a severe thunderstorm warning by the National Weather Service confirmed this.  Seeding was eventually concluded with enough material being put into the storm and additionally ceilings were beginning to lower near the convection and surrounding areas.

April 29

A reconnaissance flight took place during the evening hours as convection was moving into the target area from the northwest.  During the flight, the pilot encountered continuous light rain but not inflow.  Upon encountering the main convective cells, no inflow was found.  Convection was deemed to embedded to continue and the flight was terminated.

March 2009

March proved to be about average weather modification wise as a couple flights occurred during the month.  Due to the severity of the current drought, the season began a month earlier this year, but flight activity did not take place until March, which is climatologically when thunderstorms start to return to the south Texas landscape.  Even though two missions did take place during the month, both missions were cut short due to low ceilings.  Low ceilings are particularly a problem when seeding at base during the spring and fall months across the area.  A very dry winter continued to be a very dry spring across most locations in the target area which can be seen very well in the precipitation totals and precipitation map for the month below.  As well, a link to the flight activity spreadsheet for the month can seen below.  A total of two seeding flights on two seeding days took place this month with a total of 31 flares and 1,240g of AgI used.

Click here to view March 2009 Flight Activity

March 2009 Precipitation Map

March 11

A strong cold front was located north of the area with an upper level trough to the west of the area.   Convection started to occur during the early morning hours but ceilings were below 2000 feet and cells were embedded in light rain.  Convection continued later into the day but ceilings did start lift.  Convection occurred in Uvalde and Zavala counties and a seeding flight was launched on it.  Light rain was occurring during the flight but flares were fired during the small times when rain was not occurring.  Rain continued to get heavier and cloud ceilings were once again lowering, therefore the mission was concluded due to these reasons.

March 26

Destabilization of the atmosphere occurred quickly this morning ahead of an upper level jetstreak and a mid level vorticity maxima. This increasing instability lead to cells initiating in Uvalde County were the nose of the high instability existed.  Once again, ceilings were an issue early on, but gradually a flight was able to be launched on convection in Uvalde and Zavala counties.  Convection was elevated and the pilot was required to attain a high altitude in order to find inflow.  More flares would have been fired but ceilings dropped during the last part of the flight and the pilot was forced to terminate flight.