Purpose of the South Texas Weather Modification Association
Using aircraft, our goal is to add hydroscopic growth particles to clouds to encourage more
precipitation to form. Benefits from additional precipitation include:
- Increased agricultural production (both crop and livestock)
- Decreased surface and ground water consumption
- Improved opportunities for economic stability and future growth
- Enhanced landscape appearance
- Increased reservoir levels
- Replenishment of aquifers
- Improved habitat conditions for wildlife
- Increased lake and river levels
- Fire suppression
South Texas Weather Modification Association
South Texas Weather Modification Association History 1996 - 2011,
2016 - Present
The South Texas Weather Modification (STWMA) was formed. It consisted of representatives
from seven counties in south-central Texas: Atascosa, Bee, Frio, Karnes, Live Oak, McMullen,
Our first year of seeding commenced in May, with the radar site located at Stinson Field, San
Antonio. The radar, planes (two twin-engine planes), pilots, and meteorologist were all
contracted from Atmospherics, Inc. out of Fresno, CA. The seeding period ran from May
through the end of September. Top seeding was exclusively performed, using both
hygroscopic materials and silver iodide (AgI) in flares and generators mounted on the planes.
This year saw a number of advances for the STWMA. Early in the year, the association was
fortunate enough to purchase a WSR-74C radar, which at one time was commissioned at
Corpus Christi. The radar was installed at the Pleasanton Municipal Airport in Atascosa
County, and a small building was built beside the tower to house its components and the
In May, at the very start of the seeding season, Tommy Shearrer and Mike Mahoney traveled
to Texas Tech University in Lubbock to interview three candidates for the position of
meteorologist. Todd Flanagan became the newest addition to the project and moved to
Pleasanton in July. He began work in August, interning under AI meteorologist Alan Horn.
The season got off to a dry start in May, and it wasn't until August when the rains began.
August was a particularly busy month, with 33 flights sent out. The rest of the season went
well, ending September 30th.
Before the seeding season's end, the TNRCC granted the STWMA a four year permit to seed,
good through 2002.
The next major events for the STWMA were the purchase of a single-engine Comanche for
base seeding and the addition of its own pilot, Tim Pickens. The Comanche needed some
work before it would be ready for the 1999 season.
Todd Flanagan became the project meteorologist in charge of the program, with help from
Mark Berteau, who interned with him during the summer.
The project began officially on May 1, with one plane stationed at Stinson Field in San Antonio
and STWMA's own plane stationed in Pleasanton. Once again, all seven counties that had
participated thus far were included in the program.
This year also brought a new challenge -- coordination with other projects. Two new weather
modification projects started up adjacent to STWMA. The Edwards Aquifer project to our
north, based out of Hondo, began in April, covering counties immediately north of our project.
The Southwest Texas Rain Enhancement Association, based out of Cotulla, covered an area
from Webb County to Zavala County, to the west.
Hurricane Bret moved ashore in Kenedy County as a strong Category 3 hurricane on August
22. A day earlier, Bret’s outer rain bands moved across the target area and were seeded.
This is the first time in years (possibly since StormFury) that any part of a hurricane was
Later in the season, the STWMA purchased an additional plane (affectionately known as "Lime
Aid" due to its lime-green color), which would be worked on for the 2000 season.
It was also decided that the STWMA project would be converted into a year-long operation
from now on.
Although the project is now a year-long affair, our first seeding mission did not take place until
mid-March. By this time, "Lime Aid" was ready to fly.
A few more changes took place. Bee County left the program, reducing the size of the
program to six counties. Two new pilots, Larry Dement and Craig Funke, both from Runge
(near Kenedy), were recruited to fly for the project. They have flown on a number of missions
with Tim and are now able to do their own missions. As such, 09P was moved to Kenedy.
With our own pilots, planes, radar, and meteorologist, the project is thriving.
The project continues to progress! The first part of the year was not so great, as the
Pleasanton Airport was closed for construction (runway lengthening, addition of taxiways, and
repainting and repaving). This was finally completed by spring.
One of the Kenedy pilots, Craig Funke, left the STWMA to become chief pilot for the WTWMA
in San Angelo. This left Larry Dement as our only Kenedy Pilot. We brought back Jim
Transue, a former STWMA pilot, as a backup, keeping the number of available pilots at three.
An 80' x 80' hangar was constructed adjacent to the radar building during the spring months,
with expansion of the radar building taking place during November and December.
A third plane was purchased during the fall, which will be stationed at Pleasanton.
Overall, this year was less active than years past, but we are hoping for a change in the
weather pattern soon.
Several changes for the 2002 season were made before the end of 2001. Bee County
returned to the program after a two-year absence. The association also decided to abandon
the use of generators after tests revealed that the particle sizes in the AgI plume from
generators were too small to activate. The flare racks were expanded to hold 38 flares per
wing as opposed to the former 12 per wing. Also, our state permit was re-written to allow for
seeding in counties affected by Severe Thunderstorm, Tornado and Flash Flood Warnings so
long as the seeding did not affect the warned storm. We welcomed two pilots to the association
in the spring. Ron Merks, who worked with the program back in 1997-98 when AI was running
operations, joined us once again in 2002. In addition, Mickey Chadwell, a flight instructor at
Stinson Field, trained with us this year to become STWMA’s fifth and newest pilot. With the
additional pilots, there came another Comanche. N57AA, also referred to as “Strawberry Five”
or “Lipstick Queen” due to its iridescent pink paint, was purchased in the spring and became
operational in June.
With the departure of WMI from the EAA Precipitation Enhancement Program, seeding to our
north was halted by the end of 2001. The EAA, however, was still interested in having a
weather modification program in some of the counties. Working with the STWMA and the
SWTREA programs, they developed a contract whereupon the STWMA would annex the
counties of Bandera, Bexar and Medina into the target area for the May-September period,
and the SWTREA would acquire Uvalde County. This was to be a three-year contract, with
one of the planes (N57AA) being located at Stinson Field in south San Antonio.
Our hopes of having a busy year of seeding went down the river, so to speak, when an upper
level low parked itself over the area from the end of June into the first part of July. Tapping
into abundant tropical moisture, torrential rainfall began on June 30th and continued into the
first week of July. Some parts of the target area, mainly the northern half, received over two
feet of rain in a 10-day period. This caused extensive flooding across the area, with rivers
unable to handle the deluge of water. As such, seeding was suspended from July 1st until the
second week of August, when the soils were finally dry enough and rivers were down below
bankfull levels. Another system in early September brought another one to two feet of rain to
parts of the target area, so seeding was suspended once again. As a result of these two
flooding events, the 2002 season saw the fewest number of seeding missions in its history.
This outcome was bittersweet; we missed several convective events, but the long-term drought
was broken with the extended period of heavy rainfall.
The EAA portion of the seeding project continued, with pilots as well. The EAA contract was
extended one month to the end of October. Hurricane Claudette moved across the central and
southern target area on July 15 bringing high winds and heavy rains, but not as much rain as
one would expect with a hurricane.
2004 marked the first year of working with Weather Decision Technologies, Inc. The company,
based out of Norman, OK, provided WSR-88D data in near-real-time to all of the Texas
projects. The STWMA continued to run the WSR-74C radar at Pleasanton in tandem with the
WDT feed, and the extra data collected may be analyzed at a future date and perhaps
compared to the 88D data.
Our neighboring project, Southwest Texas Rain Enhancement Association (SWTREA) moved
their meteorologist from Cotulla to Pleasanton in early June. Then, in mid-July, a new
meteorologist – Stephanie Beall – arrived in Pleasanton to work on behalf of SWTREA. There
were some difficulties to start, mainly dealing with radio contact between the meteorologist and
the pilots, but these were fixed over time. In addition, the two projects occasionally shared
planes as well as meteorologists. We at STWMA look forward to continued camaraderie
between the two projects as we move into 2005. We also look forward to another year of
working with the EAA.
It was a busy year, with 54 days of seeding. One notable event occurred in July, when seeding
of the outer rain bands of Hurricane Emily took place over the southern target area. This was
the second time this has been done in the STWMA program; Hurricane Bret was the first, on
August 21, 1999.
Gonzales County joined the program in June. It was the busiest year as far as number of
seeding days since the inception of the program, with seeding take place on 57 days.
The STWMA welcomed a new pilot – Robert “Butch” Card, who hails from near Kenedy. South
Texas experienced several months of excessive rainfall that resulted in periodic suspensions
throughout the summer, similar to what occurred in 2002. Record rainfall totals were reported
for many areas. Due to the excessively wet conditions and the suspension periods imposed on
the project, the number of seeding days was the second lowest since the program began,
second only to 2002 during the extreme flooding in July of that year.
The STWMA, in an agreement with the EAA, began an experiment within the EAA target area
to conduct a randomized seeding experiment. The protocol was drawn up early in the season
with some guidance from NCAR, but due to the unfavorable conditions, the first randomized
missions did not take place until mid-August. Only five days of randomized missions took place
during the latter part of the season.
During the early part of the summer, two film crews came to Pleasanton to film pieces on cloud
seeding. The Discovery Channel filmed a piece on cloud seeding for their program, “Can We
Control The Weather?” which aired in August. A second crew from 4th Row Films did some
filming for a documentary on weather modification which was projected to finish sometime in
The season’s first seeding flight took place on March 18th. This was the first flight for our new
pilot, Matt Pope, who trained during the year with Craig Funke. The first few months were
disappointing as convection was sparse, so seeding missions were few and far between. The
heart of the seeding season, June-August was rather busy; June saw a lot of small, short-lived
convective cells that were treated. July and August were characterized by frequent intrusions
of tropical moisture and associated convection. Hurricane Dolly affected the area on the 23rd
and 24th, and although a reconnaissance flight took place, no seeding occurred. By
September, convection began to wind down and few opportunities for seeding presented
themselves. Hurricane Ike impacted the area as it made landfall at Galveston on the 13th, but
instead of bringing us rains, the circulation around Ike brought scorching heat, with many
locations in the target area topping out between 100-105°F. Our final day of seeding took
place on October 14th, the only day of the month that operations took place.
The NWS radar upgrade to Build 10 during the spring gave us some issues with TITAN as the
older machines were not able to handle the significant increase in data stream size, so a new
agreement was made with WDT and new machines were to be installed in February 2009
which would handle the super-resolution data.
In October, the STWMA purchased a twin engine Aztec, which incidentally was the first plane
that was used for seeding back in 1997 when the project first began. This plane will be capable
of performing top seeding as well as night seeding, both of which will be attempted in 2009.
Season number 13 saw the continuation of the drought that began the previous year, with the
vast majority of seeding opportunities on small, short-lived clouds. With the purchase of the
Aztec last year, some nighttime seeding events took place. The summer was very hot with over
60 days of highs at or above 100°F. The onset of El Niño by September brought a dramatic
shift in the overall weather patterns with much-needed rains falling across the state.
WDT installed a new computer in February that would be able to easily handle the recently-
upgraded Doppler radars to super-resolution. The computers were also assembled such that
when the anticipated changeover to Dual-Polarized radar occurs in the next few years, they will
be able to handle and process the data.
The wet pattern that began in Fall 2009 continued through a good portion of 2010 with several
months seeing well-above normal rainfall. There were a few excessive rain events that affected
South Texas and these limited seeding operations due to the threat of flooding. Tropical Storm
Hermine moved directly across the target area in September bringing heavy rains and gusty
The ongoing randomized seeding experiment within the EAA target area continued for its
fourth year but only two suitable cases were realized during the season. The amount of cases
acquired thus far falls well short of what is needed to conduct a reliable and acceptable
An intense drought plagued several southern U.S. states during the year, with the seeding
season average rainfall at less than five inches in many parts of the target area. In addition, a
record number of 100°F days were reported at Pleasanton (80). This affected operations, with
a greatly reduced number of seeding missions compared to the long-term average. 2011 also
saw the latest start to the program, with the first actual day of seeding not occurring until June
4. The pattern began to change in mid-September which allowed for several opportunities over
a two-week period to conduct seeding operations.
At the beginning of 2016 Kendell LaRoche took over the position of Project Meteorologist for
STWMA in Pleasanton. At this time 10 counties were part of the STWMA: Atascosa, Bandera,
Bee, Bexar, Frio, Karnes, McMullen, Median, Uvalde, and Wilson counties. 2016 had above
average rainfall across most of south Texas, including the operational area. Most of the heavy
precipitation took place in May, August, and September. The weather pattern across south
Texas seemed to alternate back and forth between mostly sunny with no rain, to cooler with
many consecutive days of rain during the season. The global weather pattern for 2016 started
off with a strong El Nino, which decreased to a near neutral / very weak La Nina pattern by
November. After October, there was a substantial decrease in number of rain events. The
season began slightly later than usual on April 25, while the season ended much later than
usual with 2 cloud seeding missions in November. During the season, flare dosage per storm
was increased to see if more flares lead to a greater rain turnout. Overall, the yearly
evaluation showed good results, with over 100 storms seeded, and cloud seeding activities
bringing an additional 573,370 acre-feet of water during the season.
The same 10 counties from 2016 remained. The weather pattern begins the year with a near
neutral / weak La Nina pattern. The winter months before cloud seeding began were spent
repairing aircraft equipment, updating computer software, and exploring new research
possibilities. A 'weather workshop' was held in San Angelo January 20-22. Topics included a
2016 summaries for each cloud seeding operation across TX, flare status and changes, and
possible research techniques. March was spent testing aircraft and equipment for the
upcoming season. During the end of March / beginning of April, the long time C-band radar at
the airport, which use to be used for seeding operations, was dismantled and removed. The
weak La Nina pattern began transiting to a more neutral pattern during late spring. The
season began on April 11th as a weak cold front passed through the region. A few other cold
front moved through the region throughout April, however these either did not cause any
precipitation or the conditions were unsafe for pilots (low clouds, after dark). Representatives
from STWMA, WTWMA, and Texas Tech attended the Weather Modification Association
Annual Meeting in Boise near the end of April. Presentations were given by the meteorologist
from WTWMA and STWMA on hygroscopic flare usage and Texas rainfall enhancement results
from 2016. The first cloud seeding mission for 2017 occurred in early April, however beginning
in mid April low clouds and rain occurred after sunset meant no other cloud seeding operations
were conducted until the end of May. At the end of May a strong trough stalled over the Texas
region, which sent many shortwaves into the region. These shortwaves, along with a
stationary front, caused multiple days of showers and thunderstorms across the region. The
trough eventually moved east and a strong ridge of high pressure sat over the region
beginning in early June. The strong ridge persisted across southern TX until the last weekend
in June, with a cold front stalled across the region, and brought 4 days of rain and cloud
seeding. July began with another ridge of high pressure across the region, until about a week
into July when morning and afternoon seabreeze thunderstorms became more common. July
consisted of mostly afternoon seabreeze showers and storms which would dissipate with the
loss of daytime heating. There were multiple days with no rain, however a few times a weak
low pressure would form west of the border in Mexico and move north along the Rio Grand
Plains, helping showers and storms develop. Also weak troughs would move into central TX
and occasionally as far south as San Antonio and hill country. In mid July Archie, weather
modification researcher, visited STWMA to offer guidance and test computer evaluation
programs on the computers. By the end of July/beginning of August a strong trough/cold front
moved through then stalled across the region, bringing multiple days of isolated and scattered
showers and storms. A weather modification workshop was held in San Angelo August 8-10,
with discussions on season results, new technology, and modification of seeding techniques.
After August 10, a strong high pressure system developed over the Gulf, and pushed all
moisture further east to eastern TX, and Louisiana while leaving south TX dry. The end of
August saw hurricane Harvey impact the coast near Corpus Christ, dumping tremendous
amounts of rain mainly east of the I-35 corridor. Cloud seeding was suspended for multiple
days while the region dried out. Cloud seeding resumed in early September, however other
than Sept. 4-5 the region was dominated by high pressure and slightly cooler temperatures.
Near the end of September a strong high pressure stalled over the southeastern US, which
brought warm and humid conditions to south TX. Chance of rain increased the last 2 weeks of
September, with isolated to scattered showers and storms. A few rain chances extended into
early October, however seeding only took place on Oct. 3. Most of October then became dry
with a few cold fronts which pushed through the region. However most of these cold fronts were
either took weak, or too dry to generate significant rainfall. The only strong front to generate
rain on October 31 produced stratiform rain with low visibilities. Pilot was launched and
attempted to investigate, but low ceilings and poor visibility made even getting close to the rain
dangerous. The beginning of November was similar conditions, with warm and dry conditions.
Seeding operations ended by end of the first week in November. The Pacific Ocean
temperatures were near-to-below average by the time seeding in early Nov. The yearly results
were excellent with 250 seeded storms, precipitation increased by 10.3% above the yearly
average, and 855,485 acre-feet of additional water added to the operational area.
No changes to the participating counties for 2018: Atascosa, Bandera, Bee, Bexar, Frio,
Karnes, McMullen, Median, Uvalde, and Wilson counties. The year began with a slightly cooler
than average temperatures in the Pacific. January was spent finishing the previous year
annual report and working on future projects. The STWMA and WTWMA meteorologist
attended the 98th American Meteorological Society Annual Meeting in Austin. The
meteorologist worked with the Weather Modification Association to host a booth about weather
modification during Weatherfest. The meteorologists provided information and answered
questions on weather modification. Both meteorologist also attended multiple presentations
during the Conference for Weather Modification. A summary of the 2017 season was
presented to the Weather Modification Advisory Committee in Austin in early February.