156
FXUS64 KEWX 211141
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
641 AM CDT Tue May 21 2024

...New AVIATION...

.SHORT TERM...
(Today through Wednesday)
Issued at 326 AM CDT Tue May 21 2024

An upper ridge over TX is leaning east into LA while a mostly zonal
SW aloft pattern maintains more arid conditions over the western
part of TX while deeper Gulf moisture holds over the eastern part.
Low clouds will cover nearly all areas at daybreak while dry mid
level air will become part of the mixed layer in the midday hours,
leading to a mostly sunny sky in the afternoon. In keeping with a
blend of persistence and a mix of raw data for the dew point, the
values fall a good bit in the afternoon, which should prevent most
areas from reaching heat index values associated with an advisory.
The hottest areas to the southwest will get close though. A few
pockets of 108+ heat index values can`t be ruled out in Frio and
Atascosa counties. The majority of our eastern criteria areas will
remain in the lower 100s, and the western criteria areas in the 105
to 109 range mainly today and not Wednesday. Since the hotter
pattern is expected for Friday into the weekend, we`ll stop shy of
posting the advisory and go the SPS route today and likely again
tomorrow.

There is a nonzero chance of thunderstorms in the area where the
dry air mixing hits a deeper layer of gulf moisture. This line will
probably mix as far east as Llano county, but could retreat west in
the evening. Another uncertainty is if there is any embedded
shortwave activity lifting out underneath the high cloudiness areas
from Mexico. Convective allowing models on the SPC page are quite
varied with most going for an isolated storm or two impacting our
counties while keeping most of the activity to the north. Since this
area can`t be refined in this model cycle and since the HRRR and
Tech WRF are showing little or no activity, we`ll just settle on
that and keep the messaging going that an isolated strong to severe
storm should be considered over a broad area of our northern and/or
western counties.

The messaging for storm chances is more distinct with a cold front
spawning convection and outflow boundaries over North Central Texas
and moving the convective focus southward into our counties in the
late afternoon or early evening. The broader coverage of this is
expected to be in the early part of the long term, but in short,
this could be escalated into a higher impact category of severe
potential as depicted in the depiction of severity types by the SPC
over North TX.

&&

.LONG TERM...
(Wednesday night through Monday)
Issued at 326 AM CDT Tue May 21 2024

Key Messages

* Level 1 to 2 out of 5 risk for isolated severe storms late
  Wednesday afternoon and evening across portions of the northern
  Hill Country, southern Edwards Plateau, and Rio Grande
* Dangerous heat late this week - those spending extended time
  outdoors and not acclimated to the early season heat could be
  susceptible to heat related illness if not taking proper heat
  precautions.

Isolated showers and storms will be possible late Wednesday afternoon
through the evening hours along the dryline across the southern
Edwards Plateau and along the Rio Grande. In addition scattered
storms will be possible just to our north Wednesday afternoon, across
central Texas where the dryline and weak front intersect. Wednesday
evening a few of these storms could make it into the far northern
Hill Country, or associated outflows spawning new storms. SPC has
placed portions of the Rio Grande, southern Edwards Plateau and Hill
Country in a Level 1 out of 5 risk for severe storms Wednesday
afternoon and evening, and a Level 2 out of 5 risk encompasses into
Llano and Burnet Counties. The primary threats will be large hail
and damaging wind gusts. The southern extent of the convective risk
is in question, and future outlooks may have to be trimmed back out
of the Coastal Plains and portions of the southern I-35 corridor
which are farther removed from the forcing.

The dryline Thursday and Friday looks to make slightly farther
eastward progression each afternoon, with low (10-20%) chances for
isolated storms in the afternoon and evening confined at this time
to far northeast portions of the Hill Country and central Texas.

Otherwise, continued well above normal temperatures with periods of
hazy conditions east of the dryline. Heat-related impacts are
forecast to increase each day, peaking Friday through the weekend.
During this peak, very hot afternoon temperatures of 106 to 111
degrees are forecast along the Rio Grande and U.S. 90 corridor west
of San Antonio, west of the dryline. East of the dryline, high
temperatures in the upper 90s to around 102 degrees are foreast
Friday through the weekend. Elevated dew points east of the dryline,
influences from evapotranspiration where better spring rainfall has
occurred, and the early nature of the summer heat will result in an
increased risk for heat impacts. The new NWS Heat Risk indicates an
increase into the major to extreme categories Friday through the
weekend for most areas outside of the Hill Country. Heat Advisory
headlines will likely be needed for portions for the area by Friday.
Those spending extended time outdoors and not acclimated to the early
season heat could be susceptible to heat related illness if not
taking proper heat precautions.

The upper level pattern shifts Monday as a ridge develops across the
western U.S. and trough digs through the central U.S. This may allow
a weak cold front to slip into the area sometime Monday into Tuesday
of next week, although confidence is low on timing and how far south
the front makes it given the strength of the upper level ridge just
to the south.

&&

.AVIATION...
(12Z TAFS)
Issued at 629 AM CDT Tue May 21 2024

A somewhat repetitive pattern of low cloud mornings and mostly clear
afternoons and evenings are expected. This morning there are a few
cigs around SAT flirting with IFR, but most of the obs have been in
the MVFR category. Improvement to VFR should occur by 16Z or 17Z as
the most layer remains shallow. Some gusty afternoon breezes could
again get over 20 knots at times, but there is a general trend of
lowering wind speeds forecast over the next 24 hours.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              94  76  93  75 /   0   0  10  10
Austin Bergstrom Intl Airport  94  76  93  74 /   0  10  10  10
New Braunfels Muni Airport     96  76  96  75 /   0   0  10  10
Burnet Muni Airport            92  74  90  73 /  10  10  20  20
Del Rio Intl Airport          103  81 103  80 /  10  10  10  20
Georgetown Muni Airport        92  76  92  73 /  10  10  20  10
Hondo Muni Airport             99  76  98  74 /   0   0  10  10
San Marcos Muni Airport        94  75  94  74 /   0   0  10  10
La Grange - Fayette Regional   92  76  91  76 /   0   0   0   0
San Antonio Intl Airport       96  76  96  76 /   0   0  10  10
Stinson Muni Airport           97  77  97  76 /   0   0  10  10

&&

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

$$

Short-Term...18
Long-Term...76
Aviation...18