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Area forecast discussion...updated 
National Weather Service Austin/San Antonio Texas
950 PM CDT Friday may 22 2015

Update...
weather forecast is on track for the rest of first forecast
period. Made minor changes to adjust temperatures/dew points based on
current observations.

Isolated showers/thunderstorms are still possible across the
eastern part of south central Texas tonight. However...out west
across the Rio Grande plains...scattered showers and thunderstorms
are expected overnight as a mesoscale convective system pushes across the Rio Grande.
Hires models are pointing for this feature to come in between del
Rio and Eagle Pass. Locally heavy rain is possible and cant rule
out some minor flash flooding across area roads...underpasses and
poor drainage locations. The storm complex will move to the east-
southeast and dissipates as it reaches Highway 83.

Still looking for a heavy rain event Saturday afternoon into
Sunday evening with heaviest rains expected to occur along
Interstate 35 during the overnight hours and Sunday morning.

&&

Previous discussion... /issued 650 PM CDT Friday may 22 2015/

Aviation...
scattered showers moving through the San Antonio area so included
a quick tempo group for Sat for passing convection. Other sites
will mainly be on the fringes of convection but cant rule out a
passing sh/ts over the next few hours. Satellite shows the cloud
cover thinning...being replaced by middle and upper clouds from
dissipated convection. This will be the issue for the next several
hours until low clouds start to reform. MVFR will prevail across
the taf sites after midnight with aus/Sat/ssf possibly hitting IFR
by morning with slight reductions in visibility. With the
uncertainty of when and where actual convection will fire on
Saturday...went with vicinity in the afternoon. Higher confidence
Saturday evening and into the overnight hours of more widespread
sh/ts activity. Place prevailing ts in aus/Sat late Saturday
night.

Previous discussion... /issued 244 PM CDT Friday may 22 2015/

Short term (tonight through Saturday night)...
upper air analysis this morning showed a low centered over
Southern California with the flow across Texas from the south-
southwest. At the surface a stationary front stretched across
south Texas from near Corpus Christi to Laredo. Winds across our
County Warning Area were generally from the east to southeast. Dew point
temperatures were from the middle 60s to the lower 70s. The upper
low is expected to move to the northeast and reach northern
Colorado by the end of the period. This will turn the upper flow
to southwesterly. At the same time the front to our south will
move back northward as a warm front. A series of shortwave troughs
will move through the upper pattern and along with the warm front
provide lift for convective development. Moisture will increase
tonight and early Saturday with precipitable water getting up to a maximum of 1.90
inches. This will lead to chances for heavy rain beginning
Saturday afternoon and continuing into Saturday night. Heavy rain
is likely to move across from west to east. The western part of
the County Warning Area will most likely see the bulk of their rain from Saturday
evening to Sunday morning. The eastern part will likely see heavy
rain continue into the next period. Rainfall totals of two to four
inches are likely with isolated spots getting up to six inches.
With much of the area already saturated from previous rain this
event will likely lead to flash flooding and river flooding. We
have issued a Flash Flood Watch for the entire County Warning Area for Saturday
afternoon through Sunday night. There is also a slight chance for
severe thunderstorms Saturday afternoon and evening mainly over
the west where models are showing cape around 2000 j/kg. Strong
winds look to be the main threat.

Long term (sunday through friday)...
heavy rain event should be ongoing to start this period. Main area
of heavy rain Sunday will be the eastern half of the area.
Rainfall totals are stated in the first period section of this
discussion. Our main concern is for continued flash flooding...but
there will also be a slight risk for severe thunderstorms on
Sunday. This threat will be mainly across the east and strong
winds will be the most probable result. Monday a secondary trough
will develop over the southwest and move toward the Southern
Plains. Another shortwave trough will move across Texas and bring
another chance for showers and thunderstorms Monday and Monday
night. Better chances for rain look to be north of our County Warning Area...but
with all the recent rain...runoff will be quick so any strong
storm could be a local problem. Models are a little variable
beyond Tuesday...but all want to build the subtropical ridge up
over Texas to one degree or another. At the same time low level
flow will remain southeasterly. Low level moisture will continue
to be high. So...while there does not seem to be a good forcing
mechanism...there may be isolated convection in a very moist
environment.

&&

Preliminary point temps/pops...
Austin Camp Mabry 71 82 69 80 70 / 20 60 80 70 40
Austin Bergstrom international Airport 70 83 70 79 69 / 20 60 70 80 40
New Braunfels Muni Airport 71 83 70 81 70 / 20 60 70 70 40
Burnet Muni Airport 69 80 68 79 68 / 20 70 80 70 30
del Rio International Airport 71 81 69 89 69 / 40 60 60 40 20
Georgetown Muni Airport 70 80 69 79 70 / 20 60 80 70 40
Hondo Muni Airport 71 82 68 84 69 / 30 60 80 60 30
San Marcos Muni Airport 71 81 70 80 70 / 20 60 70 70 40
La Grange - Fayette regional 72 83 72 81 71 / 20 50 50 80 50
San Antonio International Airport 72 83 69 82 70 / 20 60 80 70 40
Stinson Muni Airport 72 84 70 83 71 / 20 60 80 70 40

&&

Ewx watches/warnings/advisories...
Flash Flood Watch from Saturday afternoon through Sunday evening
for the following counties: Atascosa...Bandera...Bastrop...Bexar...
blanco...Burnet...Caldwell...Comal...De Witt...Dimmit...Edwards...
Fayette...frio...Gillespie...Gonzales...Guadalupe...Hays...Karnes...
Kendall...Kerr...Kinney...Lavaca...Lee...Llano...Maverick...
Medina...real...Travis...Uvalde...Val Verde...Williamson...Wilson...
Zavala.

&&

$$

Mesoscale/aviation...09
synoptic/grids...17
public service/data collection...30

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