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

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FXUS64 KEWX 171150

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
650 AM CDT Wed May 17 2017

The dryline will stall as mentioned below and then drift back to the
west by Thursday morning. SCT SHRA/ISOLD TSRA over the Hill Country
to along the Escarpment will shift to the east of I-35 by midday and
dissipate late this afternoon. Have -SHRA/VCSH at KAUS/KSAT/KSSF
thru 16z. SHRA/TSRA will redevelop Thursday. However, no mention in
TAFs at this time due to low PROBS. IFR/MVFR CIGs will rise to VFR
midday into afternoon with mostly SKC Hill Country and Rio Grande
Plains west of the dryline. MVFR CIGs will redevelop this evening
along I-35 and spread to the northwest overnight. CIGs will rise to
VFR midday on Thursday. S to SE winds of 6 to 14 KTs will prevail
east of the dryline with N to NW winds 5 to 10 KTs west of the


.PREV DISCUSSION... /ISSUED 405 AM CDT Wed May 17 2017/

SHORT TERM (Today through Thursday)...
Early this morning, a rapidly weakening areas of showers and storms
will continue to progress southeastward towards the I-35 corridor. As
of 330AM, a pronounced outflow boundary was leading the main
convection and while the spatial extent of shower develop was
expanding, convection intensity was decreasing to the point in which
only periodic lightning was observed. Thus, by the time this system
reaches the I-35 corridor at or just before dawn, light to moderate
showers should be all that remains.

Models are continuing to show the cold front/dry boundary to push
east into the CWA through the morning hours, stalling along the
periphery of the Edwards escarpment. Only slight chance PoPs are
expected along and east of the I-35 corridor this afternoon due to
forecast capping and significant cloud cover preventing efficient
daytime heating. Out west, much drier air will likely result in
afternoon RH values falling into the teens or even single digits in
the far western areas of the CWA. Luckily, light winds behind the
boundary should keep fire weather danger meager but will likely be
the most concerning hazard for today.

The next considerable threat for severe weather looks to be Thursday
although some disagreements still exist in the evolution and timing
of convective initiation between the GFS and ECMWF. GFS solutions
show a retrograded dry line positioned west of the Val Verde county
border with a strong low level moisture surge paralleling the dry
line by 12Z Thursday. Deterministic solutions produce isolated CI
from the Del Burro Mountains north through San Angelo. This GFS
solution seems to be an outlier however as NAM/Canadian/ECMWF and 48+
hr hi-res guidance all keep the morning hours dry Thursday. However,
during the afternoon hours, capping looks to erode allowing for
surface based parcels to interact with an environment characterized
by 40+ kts of 0-6 km shear, 3500+ SBCAPE, and 1.5-1.7" PWAT values.
Furthermore, timing of an embedded UL shortwave progged around 00Z
Friday approaching the area from the southwest will provide the added
upper level lift to result in some significant hail/wind threats late
Thursday afternoon. Initial runs of this period on the TTU-WRF show
some isolated supercell development occurring roughly around 21Z
Thursday and currently think that possibility is valid given the
agreement of convective variables in both the hi-res and synoptic

LONG TERM (Thursday Night through Tuesday)...
The aforementioned severe weather possibilities from Thursday will
likely linger through the evening hours Thursday. A brief lull in
activity should occur between 03Z and 09Z Friday before the next
piece of energy is ejected from the main upper low over the Rockies.
This will again be initially focused northwest of the CWA Friday
morning as better moisture profiles and lifting begin there. Later in
the afternoon however, a second, stronger shortwave will bring a
stout jet streak across west Texas and put the plateau counties in a
right entrance region of the jet.

By Saturday, a strong cold front will push southward through our very
moist environment characterized by PWAT values over 1.5" again. The
main question will be the evolution and progressiveness of the
frontal passage. There still exists significant disagreements in the
evolution of the frontal passage Saturday, but a more progressive
front will be the more favorable solution as a slower, potentially
stalled front could have prolonged heavy rain implications. Hopefully
later model runs will clear this uncertainty up.


Austin Camp Mabry              87  74  88  73  88 /  50  10  30  30  30
Austin Bergstrom Intl Airport  85  74  89  73  88 /  50  10  20  30  30
New Braunfels Muni Airport     86  73  89  73  88 /  50  10  30  30  30
Burnet Muni Airport            87  71  86  71  83 /  30  10  40  40  40
Del Rio Intl Airport           93  71  94  74  91 /   0  -   30  20  40
Georgetown Muni Airport        87  73  87  72  86 /  50  10  30  30  30
Hondo Muni Airport             91  73  91  73  89 /  30  10  40  30  30
San Marcos Muni Airport        85  74  89  73  88 /  50  10  30  30  20
La Grange - Fayette Regional   83  75  89  74  90 /  30  10  20  10  20
San Antonio Intl Airport       88  74  89  74  88 /  40  10  40  30  30
Stinson Muni Airport           88  74  90  74  89 /  40  10  30  30  30




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