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

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FXUS64 KEWX 081858
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
158 PM CDT Sat May 8 2021

.SHORT TERM (Today through Sunday)...

Cloud cover is showing signs of breaking up for areas along and east
of the I-35 corridor according to the latest visible satellite
imagery. Farther west into the Rio Grande plains and Hill Country,
skies are generally mostly sunny to partly cloudy. Early afternoon
temperatures are in the 80s across most of the region, except for
near 90 along the Rio Grande. Gusty south to southeast winds can
also be found across most areas.

For late this afternoon and early evening, the latest round of hi-
res models show some potential for an isolated storm to develop over
the Serranias Del Burro mountains. Any activity that manages to
develop would then move eastward toward the Rio Grande plains. While
confidence is not terribly high in this occurring, any storm that
develops could become strong to severe with hail and high winds the
main severe weather concerns. Across the remainder of south central
Texas, we will keep the forecast warm tonight with lows in the mid
60s to mid 70s. Wind speeds may not ease much after sunset as we
will still see warm temperatures and good mixing potential through
early Sunday morning. While most areas will likely remain dry, we
could see an isolated shower or two develop over portions of the
Hill Country Sunday morning.

Warm temperatures are in store on Sunday, with highs ranging from
near 100 along the Rio Grande to near 90 in the Hill Country. We do
expect to see the dryline move eastward during the afternoon hours
and it should manage to make it as far east as an Eagle Pass to
Llano line. In addition, the leading edge of a cold front will
likely move into west central Texas during the late afternoon hours.
Should storms manage to develop near the front/dryline intersection,
they would likely have a good chance of becoming strong to severe.
While it appears the favored setup for severe thunderstorms will
remain north of our region during the afternoon hours, we will need
to monitor portions of the Hill Country and adjacent I-35 corridor
from Austin northward during the evening. The front should manage to
move slowly southward during the evening hours and this could aid
thunderstorm development late Sunday evening.

&&

.LONG TERM (Sunday Night through Friday)...

South-central Texas will be entering another active period next
week, with chances for showers and storms beginning Monday afternoon
and sticking around at least into Wednesday night as mean troughing
(not particularly deep) over the western CONUS stalls out and so too
does a surface cold front somewhere across central or southern
portions of the state.

Ample low level moisture will be hanging around Monday, with dew
points and morning low temps in the 60s northwest and low to mid 70s
south and southeast. As H7 flow eventually becomes southeasterly
later in the day and SW flow above that pulls additional moisture
from the Pacific, PW values are forecast to increase into the 1.5-2"
range, highest southeast. Per NAEFS much of the region could be in
90+ percentile territory for PWats. This high atmospheric moisture
content will remain in place into the middle of the week before drier
air finally pushes in late Wednesday into Thursday. With low level
frontal forcing hanging around and and occasional upper level
impulses traversing the region, we`ll have to consider at least a low
possibility of heavy rainfall leading to localized flooding concerns
through the early part of next week. This will be especially true
for locations that are relatively saturated from all the rain we`ve
seen recently.

In addition to the threat for flooding, strong to severe
thunderstorms will also be possible. We`re already under an SPC
marginal risk outlook for Monday across the entire region, and this
may need to be upgraded over the next two days as 3-4k J/kg CAPE
will build ahead of the front with 40-50 knots of effective shear
forecast by most SREF members. The primary concern that may work
against widespread convection is the lack of a clear mid-level
shortwave to provide large-scale lift, but with the front and
dryline intersecting nearby and a little venting help provided by
the right entrance of a strengthening upper jet, global models are
bullish on QPF and several SREF members are as well. The Coastal
Plains would be least likely to see any activity but are not
entirely in the clear for Monday night.

Tuesday and Wednesday, but primarily Tuesday, could also pose
marginal severe threats as CAPE remains elevated (especially west)
thanks largely to high mid-level lapse rates in association with a
decent EML as mid to upper flow WSW comes off the higher terrain.
However, a wrench in this potential is the current NAM solution,
which indicates a rather cold airmass about 3-4 kft deep should
penetrate well south of the region, lowering severe chances
considerably. If this were to verify, Tuesday also has the potential
to be much cooler than the current forecast suggests. Not quite
ready to fully bite on that yet given a significant spread in
ensemble solutions at this time. POPs mainly sag to the southern
portions of the region Wednesday night into Thursday morning with a
drier period in store hopefully as we head into next weekend.
Temperatures should also warm back towards seasonal normals by next
Saturday.

All this is to say, there`s still a lot of uncertainty in the
forecast but several periods of showers and thunderstorms are likely
Monday afternoon through Wednesday night with low confidence in
impacts but the potential is certainly there.

&&

.PREV DISCUSSION... /ISSUED 1253 PM CDT Sat May 8 2021/

AVIATION...
Low clouds along the I-35 corridor continue to lift and scatter, with
VFR conditions ongoing or set to develop shortly. Gusty south to
southeast winds can also be expected across all areas this afternoon
and early evening. We added a mention of VCTS at DRT between 22-02Z
as some activity developing over the Serranias del Burro mountains
could move eastward toward DRT. Otherwise, winds will likely not
ease after sunset given a fairly tight surface pressure gradient and
warm temperatures helping to promote good mixing of higher momentum
winds downward to the surface. Low clouds will return to the I-35
corridor around 04Z, with MVFR cigs expected. At this time, we are
not as confident with low clouds returning to DRT and will only
mention SCT clouds at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              89  73  90  72  86 /  -   10  10  20  40
Austin Bergstrom Intl Airport  88  72  90  72  87 /  -   10  10  10  40
New Braunfels Muni Airport     90  73  93  73  89 /  10  10  10  -   30
Burnet Muni Airport            87  71  90  69  80 /   0  20  20  20  50
Del Rio Intl Airport           95  73 101  72  96 /  20  20   0   0  20
Georgetown Muni Airport        88  72  90  70  83 /  -   10  20  20  50
Hondo Muni Airport             92  71  96  71  94 /  -   -   -   -   30
San Marcos Muni Airport        89  72  91  72  89 /  10  10  10  -   30
La Grange - Fayette Regional   87  74  89  74  89 /  10  10  10  10  30
San Antonio Intl Airport       90  73  93  72  90 /  10  10  -   -   30
Stinson Muni Airport           92  73  95  74  93 /  10  10  -   -   30

&&

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

$$

Short-Term/Aviation...Platt
Long-Term...KCW
Decision Support...Morris


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