Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kewx 191127 
afdewx

Area forecast discussion
National Weather Service Austin/San Antonio Texas
627 am CDT Tue Jun 19 2018

Aviation...
at kaus/ksat/kssf, intermittent to steady rain showers continue through
tonight as a mid to upper level disturbance settles over south
central Texas. Have maintained rain showers throughout the taf period. Some
instability develops due to heating and have maintained thunderstorms and rain this
afternoon into evening from 19/17z to 20/01z. IFR cigs rise to MVFR
this afternoon. MVFR vsbys prevail, however may be IFR or VFR at
times. NE winds at ksat/kssf and east at kaus prevail with 6 to 12 kts
this morning as surface trough approaches the sites, then turns east at
all sites this afternoon into tonight. Gusts to 35 kts are possible
in and near the stronger shra/tsra.

At kdrt, VFR cigs will prevail through tonight. A brief period of
MVFR cigs is possible early this morning, however, have left out as
chances are low. Have maintained vcsh for this afternoon into
evening as rain showers are expected on the edge of the disturbance mentioned
above. East winds of 5 to 12 kts prevail.

&&

Previous discussion... /issued 337 am CDT Tue Jun 19 2018/

Short term (today through thursday)...
large area of moderate to heavy rainfall has developed just south
and southeast of our County Warning Area near the Texas coast overnight. This is
largely in response to a fairly Stout zone of surface moisture
convergence as depicted on the latest sfcoa mesoanalysis. On a
surface plot, winds over the Gulf were from the south/southeast while
overland from the east. This led to provide a surface focus for
initiation earlier tonight and we have seen the southerly winds push
farther inland over the past several hours. As a result this zone of
precipitation is slowly shifting north and is now beginning to enter
our coastal plains counties. In addition, a swirl can be seen over
Bee County which is most likely an mesoscale convective vortex which is likely helping to
aid in precipitation rates from this activity. The crp office has
reported some 4 inch per hour rainfall rates within this band.

As a result think chances for heavy rain in the short term is
increasing and our southeastern row of counties may see a quick 1-4
inches this morning as this zone of precip continues to lift north.
As a result, have opted to issue a Flash Flood Watch for Karnes,
DeWitt, and Lavaca County where the heaviest rain is expected to
fall. Farther north, some heavy rain is possible but with
precipitable water values beginning to drop off within a sharp
gradient, precip totals should be less as you travel northeast. If
this does not pan our like current forecast, the watch may need to be
expanded north later this morning.

The bulk of the rainfall has remained southeast of our area for the
past couple of days and this is mostly in part to the center of the
low remaining near the coast and our area remained on the westward
side of the low which is typically the drier side. However, in
addition to the reasoning in the previously mentioned paragraph, the
upper low is expected to move northwest throughout the day today
before stalling south of Bexar County later tonight. This should help
open things up for the eastern half of the area to see the higher
coverage of activity than we have been expecting. There will be a
sharp gradient to the pops for today with 30-50 percent west of
Highway 281 and 70s and 80s to the east. The same kind of gradient is
in the forecast for tonight with 20-40 percent west of Highway 291
and 60-70 percent to the east.

The forecast for Wednesday is a bit more uncertain. The ECMWF,
Canadian, and NAM all keep the stalled low nearly in the same place
while the GFS starts its movement to the southwest a day early. The
GFS is dry while the other members remain wet. Have opted to keep the
forecast pretty wet with likely pops remaining along and east of
i35. Because of this, kept the Flash Flood Watch in effect with an
expiration time of 00z Thursday to account for additional rainfall on
potentially saturates soils. The consensus of the guidance does
shift the upper low to the southwest on Thursday which should lower
the chances of rain. However, a strong upper low will be passing
through the Central Plains which will create a weak shear axis across
the eastern half of the area. This will warrant the maintaining of
at least chance pops for the eastern areas. Average storm total
rainfall for this event through Thursday will be less than an inch
west of Highway 83, 1-3 inches for the I-35 corridor and 4-6 inches
in the coastal plains with some isolated totals possibly exceeding 8
inches especially if the heavy rain this morning comes to fruition.
High temperatures in the short-term will be tampered with the cloud
cover and rainfall with 80s expected where the bulk of the rain is
expected.

Long term (thursday night through monday)...
will keep 20 pops in the forecast Friday for the southeastern half of
the area as residual moisture and daytime heating could lead to
isolated afternoon activity. Will show a dry forecast Saturday but 20
pops return Sunday as a weakness aloft moves closer to the area. High
temperatures will respond to the drier forecast with highs Sunday
back into the middle to upper 90s for much of the area and 100-102
temperatures closer to the Rio Grande.

&&

Preliminary point temps/pops...
Austin Camp Mabry 84 74 87 75 92 / 70 50 60 30 30
Austin Bergstrom Intl Airport 84 75 87 74 91 / 70 50 60 30 30
New Braunfels Muni Airport 85 74 88 74 90 / 70 50 60 30 30
Burnet Muni Airport 86 73 87 73 92 / 60 30 50 20 20
del Rio Intl Airport 94 77 97 77 98 / 30 10 10 - 10
Georgetown Muni Airport 84 74 86 74 91 / 60 50 50 30 20
Hondo Muni Airport 88 75 92 75 93 / 50 40 50 20 20
San Marcos Muni Airport 84 74 88 74 91 / 70 50 60 30 30
La Grange - Fayette regional 83 75 86 75 90 / 80 70 70 40 50
San Antonio Intl Airport 86 75 90 75 91 / 70 50 60 30 30
Stinson Muni Airport 86 76 90 75 91 / 80 50 60 30 40

&&

Ewx watches/warnings/advisories...
Flash Flood Watch through Wednesday evening for De Witt-Karnes-
Lavaca.

&&

National Weather Service Glossary of Abbreviations