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

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FXUS64 KEWX 141138
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
638 AM CDT Thu Mar 14 2024

...New AVIATION...

.SHORT TERM...
(Today through Friday)
Issued at 205 AM CDT Thu Mar 14 2024

Key Messages...

* Confidence in storms developing across South-Central Texas during
  this afternoon and evening remains low and conditional on the
  capping inversion breaking.
* Friday has greater potential for isolated to scattered strong to
  severe thunderstorms with primary threats of large to very large
  hail and damaging winds.
* In addition to the severe threat on Friday, storms could produce
  locally heavy rainfall with robust rainfall rates and potential of
  isolated flash flooding.

Discussion...

Low stratus will dominate this morning with perhaps a few locations
seeing patchy drizzle. Spotty light showers could develop with the
moisture trapped underneath the capping inversion across the Hill
Country and our northern most counties from the morning into the
afternoon hours. With low stratus expected to hold strong at least
into the early afternoon hours, this should help to delay and limit
the amount of surface heating across that region. This remains an
important detail as greater amount of surface heating would make a
difference on the possible erosion/breaking of the cap. Latest CAM
guidance continues to hold the capping inversion across our region
and the low thunderstorm chance in our region remains contingent on
that cap breaking. If any storms are able to overcome the odds of
breaking the cap, they could become severe with large hail and
strong winds as the primary hazards, as result of the supportive
environment with moderate instability and deep layer shear. For the
locations out west, the dryline should move east enough for clouds
to break earlier and for humidity levels to tank along the Rio
Grande and for temperatures to warm into the low to mid 90s.

First half of Thursday night should stay on the quieter side with
returning low stratus and area high level clouds. A shortwave then
approaches out of the southwest and coincides with the slowed
approach of a cold front from the north. Several HREF CAM members
fire convection from the overnight into Friday morning with the
greatest focus in our northern zones. While this activity may be
elevated initiating above the cap, they could become strong to
severe with the amount of instability that still exists above the
inversion. The primary hazard associated with these cells would be
large to very large hail. Activity could briefly fall into a lull
before additional convection fires along or near the surface front
during Friday afternoon as the front continues to make its slow
progress southward. This activity will also have the potential of
becoming strong to severe with the main hazards of large to very
large hail and damaging straight line winds. If a storm is able to
root to the surface into the coastal plains, an isolated tornado
could be possible as well. Given these two potential rounds of
convection, SPC has highlighted a level 2 of 5 risk for locations
along and east of the I-35 corridor and a level 1 of 5 risk across
the rest of our CWA on the recent release of the Day 2 convective
outlook. Strong to severe storms will also be capable of locally
heavy rainfall with at times intense rainfall rates. This could
result in isolated flash flooding across portions of the region on
Friday despite the recent dry spell across our area. WPC has also
recently added a level 2 of 4 risk for excessive rainfall leading to
flooding over the eastern half of south-central Texas while the
level 1 of 4 risk extends across the remainder of the region on the
new day 2 excessive rainfall outlook. Temperatures for Friday top
out in the 70s to the north behind the front and in the 80s to low
90s for locations to the south and west who are last to have the
front push through.

&&

.LONG TERM...
(Friday night through Wednesday)
Issued at 205 AM CDT Thu Mar 14 2024

Key Messages...

* There is high confidence in rain chances Friday night through
  Sunday across south-central Texas.
* A few strong to marginally severe storms capable of producing hail
  will be possible during this time.
* Pockets of heavy rainfall are also possible during this time,
  which could produce localized flooding.

Discussion...

The upper level low is forecast to remain across the southwest U.S.
through Wednesday. South-central Texas will remain in an active
southwest flow aloft through this time.

Ongoing convection and cold pooling along the front early Friday
evening should drive the front into south Texas Friday night. The
front is shallow, and models have been very consistent run to run
with an approaching mid-level shortwave in the southwest flow aloft
producing isentropic ascent and lift overnight across western and
southern areas, spreading northeast through the remainder of the
region on Saturday, which will lead to the development of elevated
showers. Forecast soundings indicate mid level lapse rates around 7
deg C/km and a pool of modest CAPE above the frontal inversion. So a
few strong to marginally severe hail producing storms could be
possible. Some pockets of locally heavy rainfall will also be
possible.

A second, more robust shortwave is forecast to move through the
region Saturday night into Sunday morning. This will have the
potential to produce more widespread, heavier rainfall across
portions of the area, in addition to another threat for strong to
marginally severe hail producing storms. There is some uncertainty
on where the actual cold front could end up Saturday into Sunday,
with some models lifting it back north into the inland Coastal
Plains, and this could also serve to focus a band of enhanced
rainfall along and north of it.

12Z Saturday to 12Z Sunday ECMWF ensemble probabilities of a
widespread 1/2 to 1 inch of rainfall across the I-35 corridor and
Coastal Plains are 50-90%, with a 30-60% chance of 1 to 2 inches
near and east of I-35 and near and south of I-10. GEFS probabilities
are slightly lower and displaced slightly farther north. WPC has
expanded the Level 2 of 4 risk for excessive rainfall producing
flooding southwest, encompassing all of the southern I-35 corridor
and Coastal Plains.

Beyond Sunday the forecast confidence decreases. A secondary cold
front is indicated Monday, with drier air backdooring into the
central and eastern areas into Tuesday. A pool of better moisture
and rain chances is forecast to remain along the Rio Grande Monday
night through Tuesday. Eventually the upper level low is forecast to
open into a trough that moves across Texas sometime Wednesday night
or Thursday, but again this is low confidence. Ahead of it, rain
chance could expand back east through the area Wednesday and
Thursday.

&&

.AVIATION...
(12Z TAFS)
Issued at 638 AM CDT Thu Mar 14 2024

Stratus prevails across most of south-central Texas early this
morning and was producing MVFR ceilings. The stratus will gradually
erode near the Rio Grande and western Hill Country later this
morning and more slowly across the eastern Hill Country and along and
east of the I-35 corridor this afternoon, with ceilings becoming
VFR. Stratus is forecast to re-develop from east to west 02Z-09Z
tonight, producing mainly MVFR ceilings with some pockets of IFR
ceilings.

A few -SHRA will be possible beneath the cap late morning through
the afternoon north of a T82-AUS-GYB line. We will watch closely
late afternoon and evening to see if the cap erodes enough to allow
deeper convection just to the north to build south towards AQO-BMQ-
GTU. If the cap does erode, storms near and north of the line could
become severe and contain large hail and gusty winds. Then attention
turns to early morning Friday, where a disturbance aloft could
generate isolated to scattered SHRA/TSRA activity 10Z-16Z Friday
from southwest to northeast across the region. A break in the
convection could occur late Friday morning into the early afternoon,
and then scattered TSRA activity is expected mid afternoon Friday
through Friday night along and ahead of a cold front. Storms Friday
could be severe, containing very large hail and damaging wind gusts.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              79  67  74  60 /  20  40  70  20
Austin Bergstrom Intl Airport  80  67  75  58 /  20  40  70  20
New Braunfels Muni Airport     81  67  77  61 /  10  30  60  30
Burnet Muni Airport            78  64  70  56 /  30  50  70  20
Del Rio Intl Airport           91  67  85  63 /   0  20  30  60
Georgetown Muni Airport        79  65  72  57 /  30  50  80  20
Hondo Muni Airport             85  66  82  59 /  10  30  50  30
San Marcos Muni Airport        80  67  76  59 /  20  40  70  30
La Grange - Fayette Regional   82  70  80  63 /  10  40  60  30
San Antonio Intl Airport       82  67  78  61 /  10  30  60  30
Stinson Muni Airport           85  68  80  62 /  10  30  50  40

&&

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

&&

$$

Short-Term...Brady
Long-Term...76
Aviation...76


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