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

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FXUS64 KEWX 271211 AAA

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
711 AM CDT Wed May 27 2020

/12Z TAFS/
Mostly clear skies this morning across area sites with few high
clouds coming into the northern Hill Country with no impacts to the
I-35 terminals. VFR conditions remain for all area sites through late
this afternoon before storms begin to develop across the northern
part of the Hill Country to then move to the southeast. MVFR and
even IFR vsbys are possible as thunderstorms move over or nearby
KAUS/KATT. We kept the TEMPO group for both KSAT and KSSF for the 01Z
hour through 03Z Thursday as of best guess for storms to affect the
San Antonio terminals. VFR conditions are expected at KDRT for the
entire forecast period. Winds are expected to be out from the south
and southeast through late this afternoon with wind shifting to the
northeast and even becoming light and variable late tonight into
Thursday morning.


.PREV DISCUSSION... /ISSUED 334 AM CDT Wed May 27 2020/

SHORT TERM (Today through Thursday)...

Strong to severe thunderstorms capable of producing large hail and
wind gusts of 60 mph are expected late this afternoon into the
evening hours along and east of a Juno to Uvalde to Pearsall line. A
more significant risk for severe thunderstorms exists along and east
of a Kerrville to New Braunfels to Schulenburg line. The Storm
Prediction Center Day 1 Convective Outlook has the above mention area
under Enhanced Risk of Severe Thunderstorms with storms affecting
this area capable of producing very large hail of 2 inches in
diameter or greater and significant wind gusts of 75 mph or greater.
Isolated tornadoes are also possible.

Below is the break down of how things are expected to play out today
and tonight. Partly cloudy to mostly sunny skies are expected this
morning through the mid afternoon. Temperatures will climb into the
mid to upper 80s across the Hill Country to lower 90s along the Rio
Grande. We should be rain-free for most of the morning period. From
here on out, the trouble starts with good insolation in place and
surface southerly flow increasing ahead of a weak frontal boundary
across central Texas.

By late afternoon, a short-wave traveling around the upper level low
pressure over southeast Oklahoma is forecast to push into the Hill
Country. Isolated storms are forecast to develop late this
afternoon around Williamson and Burnet areas. They are expected to
become super cellular and rapidly congeal into a cluster/line of
severe storms around 5 to 6 PM and last through about midnight.
Lingering showers and storms are expected past midnight, however,
the severity of the storms should be less.

Area forecast soundings show MUCAPE values in the order of 2000 to
2500 J/Kg and as high as 3500 J/KG by a few of the SREF plume
members. Effective shear values are in the order of 50 to 60 knots
across the Hill Country including the Austin metro area with the
SREF plume models showing similar shear values. Mid-level lapse
rates are around 7.0 C/km which support deep convection with DCAPE
values ranging from 800 to 1000 J/Kg which support strong downdraft.
One more thing, LCLs signatures are showing between 850mb and 700mb
from both GFS and NAM forecast soundings which values are not ideal
for tornadoes to form, however, shear values are there for rotating
storms. All this to say, the atmosphere will be prime for severe
weather this afternoon and evening is all the ingredients come

The storm activity should come to an end for most area overnight
with a few lingering storms across the southeast counties of south
central Texas. We do have a 20 percent chance for showers/storms on
Thursday morning across parts of the Hill Country down to the
coastal Plains as few HiRes models show a line of storms oriented
from north to south. Showers and storms return across the northeast
and southeast of the area as another short wave disturbance push
down into our area within the western periphery of the upper level
low pressure system.

LONG TERM (Thursday Night through Tuesday)...

Some good news many folks will appreciate: a much quieter period of
weather is in store through the weekend and much of next week. By
Thursday evening, the upper low will thankfully be well on its way
to the Great Lakes as it gets picked back up by a nrn stream trough.
Precip chances overnight and on Friday should be relegated to the
southwestern third of the area where better moisture will exist and
some light upslope flow will aid in initiation of thunderstorm
activity. Some weak low to mid-level troughing near the Rio Grande
will likely be convectively enhanced during this period. However,
storms should quickly push off to the south as broad central CONUS
sfc ridging builds during the day.

Although the upper level ridge will remain to our west much of the
weekend, it is expected to amplify slightly and slowly cross
eastward through the first half of next week, reaching the eastern
CONUS by Wednesday evening. At this time, any precipitation chances
past Friday look low and relegated mainly to  far southern and
western portions of our area away from the high-pressure induced
subsidence that will dominate much of the Plains. Although perhaps
not as stagnant as some examples, this setup is looking pretty
reminiscent of what`s referred to as a "ring of fire" where
disturbances ride the ridge and bring daily thunderstorm chances
from the upstream side of the ridge northeastward to the northern US
and into Canada. But for us here we will have to rely on sub-
synoptic processes if we are going to see any precip of note (which
at this time is unlikely for most of the area). Temperatures are
generally expected to be seasonal, with highs in the 80s to mid 90s
and lows in the 60s and lower 70s.


Austin Camp Mabry              87  65  87  66  87 /  50  60  20  10  -
Austin Bergstrom Intl Airport  88  64  86  66  87 /  40  60  30  10  -
New Braunfels Muni Airport     89  65  89  66  88 /  20  30  20  10  -
Burnet Muni Airport            85  63  85  63  85 /  60  70  20  10  -
Del Rio Intl Airport           93  71  93  70  93 /   0   0  -   50  20
Georgetown Muni Airport        87  64  86  64  86 /  80  80  30  10  -
Hondo Muni Airport             89  67  92  67  91 /   0  10  10  20  10
San Marcos Muni Airport        88  64  88  65  88 /  20  40  20  10  -
La Grange - Fayette Regional   86  66  87  66  87 /  50  50  30  10  -
San Antonio Intl Airport       89  67  90  68  90 /  -   20  10  20  10
Stinson Muni Airport           91  68  91  69  90 /  -   20  10  20  10




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