Special Weather Statement, NWS Austin/San Antonio, TX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
426 PM CDT Mon Apr 17 2017

.SHORT TERM (Tonight through Tuesday Night)...
Scattered to widespread showers and thunderstorms have developed as
expected for areas mainly along and east of Highway 281 as a closed
low/MCV at midlevel currently over Guadalupe-Gonzales-Caldwell
Counties slowly pushes east. Additional isolated storms that are
more instability driven and progressive (and behaving like a feeder
band into the MCV during mid-April!) are developing west of the MCV
towards Medina and Uvalde Counties. The 15-20 knot low level jet
east of the MCV that helped cause 2-3 inches of rain over eastern
Lavaca County early this afternoon has weakened and pushed east of
the region. However, a second area of heavy rainfall that developed
just north of the MCV a few hours ago over central and southern Comal
County caused up to 3-4 inches of rain, triggering a Flash Flood
Warning with some road closures. Although most areas should receive
below one inch of rain for the rest of the afternoon and early
evening hours, we cannot rule out some isolated 2-3 inch totals
falling within an hour near the MCV circulation over Guadalupe County
that should continue to slowly track east or remain fairly
stationary. Thus, some flood advisories and perhaps an isolated
instance of flash flooding will be possible in and surrounding these
counties over the next few hours, while other areas should remain
below an inch with more progressive storms.

Although we expect that most storms will end later this evening as
the atmosphere stabilizes over most of the region, there is still a
chance that the complex located just south of the I-20 corridor may
hold together as it pushes south into our region this evening. Thus,
we have maintained 30-40 POPs this evening with 20-30 POPs overnight
to account for this possibility, but the evening shift may be able to
take this out based on stability profiles and radar trends later. Of
greater concern is the possibility of redevelopment of convection in
the vicinity of the MCV overnight as a 15-25 knot southeasterly LLJ
redevelops with isentropic ascent on the east side of the MCV
providing additional lift. In addition, PWATS will be approaching
1.5-1.7 inches and model soundings at VCT indicate this environment
may have a weak cap or none at all. Hi-res models are working to
catch up to the current feature, but it looks like the most likely
area for this to occur would be east of the I-35 corridor and along
and south of the I-10 corridor in our southeastern most counties.
Locally heavy rainfall will be possible, which will be a greater
problem if it falls over areas that have already received a few
inches of rain and thus will be more susceptible to flash flooding.

Considering this is more of a warm season environment adjusted down
about 10-15 degrees for April, tomorrow's forecast is relatively
uncertain as it will be dependent on the location of the MCV and
whatever convection materializes tonight. However, at the current
moment it looks like isolated to scattered showers and thunderstorms
will continue to develop tomorrow mainly along and east of Interstate
35 as the MCV gradually slides to the east or southeast, with the
best chances over our southeastern-most counties. Rain totals should
be more modest tomorrow afternoon than they may potentially be
overnight, but additional saturation and any locally heavy downpours
will still warrant an isolated flash flood threat. Nevertheless, a
watch is currently not anticipated at this time given the uncertainty
of the forecast and very isolated nature of the flash flooding.

&&

.LONG TERM (Wednesday through Monday)...
A mid-to-upper level ridge of high pressure and its associated
capping inversion will begin to build from the southwest on
Wednesday which will keep isolated shower and thunderstorm chances
confined to our far southeastern counties. The ridge will build
further on Thursday to keep the entire region dry with highs in the
mid 80s to lower 90s. A trough digging in from the Rockies will
deepen over Kansas on Friday into Saturday to help pull a relatively
strong cold front through the region on Saturday morning which both
the ECMWF and GFS agree upon now. Considering dynamic forcing
associated with the upper level low will be well north to our region
and the morning frontal passage is not exactly optimal for shower and
thunderstorm develop, it looks the chances the region will be dry
slotted with little or no rainfall is looking greater. However,
considering only a few model cycles have shown this, we have
continued 20-30 POPs over the eastern two-thirds of the region. Drier
and cooler than normal conditions will be expected on Sunday behind
the front before gradually warming back up for Monday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              64  80  66  84  67 /  40  30  10  10  -
Austin Bergstrom Intl Airport  62  79  64  84  66 /  40  30  10  10  -
New Braunfels Muni Airport     64  80  64  84  66 /  40  30  10  10  -
Burnet Muni Airport            61  78  63  83  66 /  40  20  -   -   -
Del Rio Intl Airport           64  85  66  88  67 /  30  10  -   -   -
Georgetown Muni Airport        61  78  64  83  66 /  40  30  10  10  -
Hondo Muni Airport             63  83  65  86  66 /  30  20  10  10  -
San Marcos Muni Airport        63  80  64  84  66 /  40  30  10  10  -
La Grange - Fayette Regional   66  78  65  84  67 /  40  40  10  20  -
San Antonio Intl Airport       64  81  66  84  67 /  40  30  10  10  -
Stinson Muni Airport           65  80  66  85  67 /  40  30  10  10  -

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

Mesoscale/Aviation...TB3
Synoptic/Grids...LH
Public Service/Data Collection...Treadway

Hazardous Weather Outlook
National Weather Service Austin/San Antonio TX
431 AM CDT Mon Apr 17 2017

TXZ171>173-183>194-202>209-217>225-228-180945-
Llano-Burnet-Williamson-Val Verde-Edwards-Real-Kerr-Bandera-
Gillespie-Kendall-Blanco-Hays-Travis-Bastrop-Lee-Kinney-Uvalde-
Medina-Bexar-Comal-Guadalupe-Caldwell-Fayette-Maverick-Zavala-
Frio-Atascosa-Wilson-Karnes-Gonzales-De Witt-Lavaca-Dimmit-
431 AM CDT Mon Apr 17 2017

This Hazardous Weather Outlook is for South-Central Texas..

.DAY ONE...Today And Tonight.

Locally heavy rain is possible this afternoon southeast of I-35
and east of I-37.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter reports may be needed this afternoon.

Special Weather Statement
National Weather Service Austin/San Antonio TX
105 PM CDT MON APR 17 2017

TXZ209-223-225-171845-
Lavaca TX-Fayette TX-Gonzales TX-
105 PM CDT MON APR 17 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN GONZALES...FAYETTE
AND LAVACA COUNTIES UNTIL 145 PM CDT...

At 103 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles west of Moulton to 10 miles south of
Speaks. Movement was north at 30 mph.

Heavy downpours, frequent cloud to ground lightning, small hail, and
wind gusts in excess of 40 mph will be possible with these storms.

Heavy rainfall may result in minor flooding impacts such as flooded
low water crossings and ponding on roadways.

Locations impacted include...
Gonzales, Yoakum, La Grange, Schulenburg, Hallettsville, Shiner,
Flatonia, Moulton, Shelby, Waelder, Fayetteville, Round Top, Sublime,
Muldoon, Cistern, Ezzell, Speaks, Carmine, Komensky and Swiss Alp.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Austin San Antonio.

&&

LAT...LON 2907 9694 2938 9724 2937 9725 2963 9760
      2978 9732 3005 9703 3003 9701 3011 9685
      3016 9680 3014 9676 3017 9669 3014 9665
      2996 9657 2963 9687 2961 9684 2958 9683
      2958 9679 2934 9656
TIME...MOT...LOC 1803Z 180DEG 38KT 2959 9726 2910 9677

TB3

Special Weather Statement
National Weather Service Austin/San Antonio TX
452 PM CDT MON APR 17 2017

TXZ203-172230-
Uvalde TX-
452 PM CDT MON APR 17 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN UVALDE COUNTY UNTIL
530 PM CDT...

At 451 PM CDT, Doppler radar was tracking a strong thunderstorm near
Sabinal, moving south at 10 mph.

Dime size hail and brief heavy rains are possible with this storm.

This storm will remain over mainly rural areas of southeastern Uvalde
County along FM 187.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 2918 9959 2931 9949 2930 9941 2928 9941
      2914 9943
TIME...MOT...LOC 2151Z 011DEG 5KT 2926 9946

CP