Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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FXUS64 KEWX 260620

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
120 AM CDT TUE JUL 26 2016

A line of SHRA and TSRA stretching from CZO to east of COT
continues to push southwest. Light showers in the vicinity and
20-25 knot gusts associated with an outflow boundary will continue
for the next hour or so at DRT, whereas rain has cleared the I-35
TAF sites. A stable atmosphere should keep the rest of tonight and
the morning hours relatively quiet at all TAF sites. Ceilings
will generally remain VFR due to the stable atmosphere and calm
winds aside from a brief period of broken MVFR ceilings above 2000
feet at the I-35 sites late tomorrow morning. However, patchy fog
may develop after 10Z at AUS and SSF due to moist soils from
rainfall received today and the calm winds.

The broad inverted trough currently off the Louisiana Gulf Coast
will move west into South Texas tomorrow, triggering scattered to
widespread afternoon showers and thunderstorms. Remnant boundaries
left behind by this afternoon and evening`s convection will help
focus storm development tomorrow afternoon. Hi-res models are
beginning to trend towards having greater coverage over the
southern and western halves of our CWA, which will likely have
stronger boundaries left behind and greater differential heating
than the northern half. For now, have indicated this in the TAFs
by carrying a longer period of VCTS for DRT and SAT/SSF from
19-01Z than at AUS which only has them from 21-00Z.



Isolated to scattered showers and storms have continued to slowly
progress farther southwest into the Austin area and surrounding
locations through 7 PM. So far, this convection has resulted in
some very localized rainfall totals of between 1 and 2 inches,
namely in the Jollyville area in Travis County. Some half inch to
inch amounts were seen with earlier cells in northern Bexar and
Comal counties.

Latest HRRR and TTU WRF show this activity continuing to push
southwest and persist until about midnight. Most concernable
factor is high PWATs this evening, namely 2"+ from the I-35
corridor and east, maxing out at 2.4" near College Station. Thus,
isolated heavy rainfall will continue to be a threat with this
activity through the evening hours. Should this activity congeal
into more organization...some spots could see a quick 2+ inches
of rainfall...wherever that occurs. Could result in some minor
urban flooding.

As a result, increased PoPs for the evening hours and accounted
for the decrease in coverage noted in the high res suite after



Scattered TSRA is ongoing just north and west of KAUS and is over
KATT as of 2345z. A wind shift to the east due a localized gust
front is moving through KAUS currently with gusts to near 15-20
knots. Winds will weaken to near 10 knots within the next hour
and return more southeasterly. Additional TSRA is located farther
north and east of KAUS and KSAT and this could impact both sites
periodically through the evening. Have placed TEMPO group in for
this activity as it slowly decreases after 05Z.

A strong outflow boundary is east of KAUS/KSAT as of 2345Z and
could help develop renewed TSRA activity farther south towards
KSAT/KSSF. For this reason, have also placed a TEMPO group there.
KDRT will be clear of most TSRA this evening as Hill Country
storms should diminish before reaching the Rio Grande Plains.

A lull in activity is expected late overnight and through morning
but scattered to numerous TSRA is expected to redevelop near and
after 18z for most TAF sites Tuesday. Have placed VCTS in for now
and will likely add direct TSRA wording on either the 06Z or 12Z
TAFs when timing and coverage confidence increases based on
latest trends.


SHORT TERM (Tonight through Tuesday Night)...
The latest water vapor satellite loop shows a weak upper
disturbance over east Texas this afternoon. The water vapor loop
also shows a broad area of low pressure and convection over the
northern Gulf of Mexico. The satellite-derived total precipitable
water product shows moisture levels have increased today with
current values ranging from 1.75" along the Rio Grande to 2.0"
over the coastal plains.

The upper level disturbance over east Texas will drift
southwestward into south central Texas through tonight. Daytime
heating along with increased moisture will result in scattered
showers and thunderstorms this afternoon and evening. We have
already seen an increase in convective activity this afternoon and
with continued heating, this trend will continue. Most activity
will likely be tied to daytime heating. However any remnant
outflow boundaries and subtle lift should continue isolated to
possibly scattered convection tonight. The upper disturbance
currently over east Texas will drift west of the Rio Grande by
Tuesday afternoon as the broad low in the Gulf slowly moves
westward toward the region. With continued moisture advection and
daytime heating, our rain chances will increase into the 50-60% on
Tuesday. Given plenty of moisture (PWATs of 2.0-2.3") and slow
storm movement, can`t rule out some locally heavy rainfall. It
will be difficult to pinpoint where the heaviest rain will occur
as much will likely depend on any remnant outflow boundaries from
earlier convection.

LONG TERM (Wednesday through Monday)...
Broad, cyclonic flow aloft and deep layer moisture will persist
across south central Texas on Wednesday. This along with daytime
heating should be enough to generate another round of scattered
convection, mainly during the afternoon and evening hours. For
now, we will keep rain chances in the 30-50% range, but this may
need to be increased if subsequent model trends remain consistent.
The broad area of low pressure aloft continues to weaken on
Thursday, leaving a col over south central and eastern Tx. Rain
chances will decrease, but given plenty of moisture and daytime
heating we should see at least isolated diurnally-driven
convection across most of the region. Temperatures will also begin
to creep upward on Wednesday and Thursday, but are forecast to
remain near climatological normals. The upper pattern changes
little through the end of the week, but the atmosphere will begin
to slowly dry out. While we can`t rule some additional isolated
convection over most areas, suspect the coastal plains will be
favored given the afternoon sea breeze. Temperatures will also
rise back to above normal with lows in the 70s and highs in the
mid 90s to near 100.


Austin Camp Mabry              94  76  96  76  96 /  60  30  40  20  30
Austin Bergstrom Intl Airport  93  75  94  76  96 /  60  30  40  20  30
New Braunfels Muni Airport     94  75  95  75  96 /  60  30  40  20  30
Burnet Muni Airport            92  74  94  75  93 /  50  30  40  20  30
Del Rio Intl Airport           97  77  97  78  98 /  50  20  30  20  20
Georgetown Muni Airport        92  75  94  76  93 /  50  30  40  20  30
Hondo Muni Airport             94  75  95  75  97 /  60  20  40  20  20
San Marcos Muni Airport        93  75  94  75  95 /  60  30  40  20  30
La Grange - Fayette Regional   93  76  95  77  95 /  60  30  50  20  40
San Antonio Intl Airport       93  77  95  77  95 /  60  30  40  20  20
Stinson Muni Airport           95  77  96  77  98 /  50  30  40  20  20




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