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

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FXUS64 KEWX 161805
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
105 PM CDT Tue May 16 2017

.AVIATION.../18Z TAFS/
MVFR ceilings have continued into the afternoon at all sites with
some isolated IFR ceilings in the Hill Country due to isentropic
ascent and Gulf moisture overspreading the region. Ceilings should
gradually lift to VFR from the Mexican Plateau and Coastal Plains
inwards, allowing AUS to become VFR first within the hour and DRT and
SAT/SSF becoming VFR between 20-21Z. Very strong capping inversions
evident around 800 mb will prevent thunderstorms from developing at
AUS and SAT, but a isolated thunderstorm is possible at DRT early
this evening between 0-2Z if a cell is able to develop in Mexico and
hold together east into a relatively strong cap at DRT. The only
model that shows this occurring is the Texas Tech WRF, so this has
not been included in the DRT TAF since chances are below 20 percent.

Ceilings will lower to MVFR between 4-6Z at all sites as a decaying
line of showers and possibly thunderstorms moves through DRT between
7-10Z and AUS/SAT between 10-14Z. Confidence in thunderstorms is too
low to include VCTS at any site at this time, but confidence is high
enough to include prevailing showers at the I-35 sites. Although the
chance of precipitation is lower at DRT relative to the I-35 sites,
the chance of thunderstorms occurring there is greater as the cap
aloft will be a bit weaker, so for now have included VCSH there.
Future amendments and TAF issuances will continue to evaluate the
situation to upgrade sites to include VCTS or prevailing TSRA as
conditions warrant. Ceilings may lower to IFR with the passage of
the line of showers before ceilings improve to MVFR by mid-morning
and VFR by the afternoon at all sites (mid-morning at DRT).



&&

.PREV DISCUSSION... /ISSUED 637 AM CDT Tue May 16 2017/

AVIATION... /12Z TAFS/
Am expecting a similar trend to that of Monday in terms of ifr cigs
showing up around daybreak, so the current TAF forecast will be a bit
on the pessemistic side for a couple hours should the ifr cigs fail
to materialize. There is more morning wind at this time compared to
Monday, but also slightly higher dewpoints and a deeper low level
moisture layer. Slow but steady improvements back toward vfr skies
should develop by early this afternoon with the I-35 terminals
suggested to mix a bit faster than at DRT. Isolated storms could
impact DRT in the evening and late night hours but are only suggested
as a vcts from 4Z to 10Z. Higher chances for rain and a few storms
are expected along I-35 later in the period, but the potential for
significant storm impacts such as hail and high winds will be much
higher at DRT than along I-35.

PREV DISCUSSION... /ISSUED 430 AM CDT Tue May 16 2017/

SHORT TERM (Today through Wednesday)...
An upper level trough currently along the California/Arizona border
will move rapidly to the Southern high Plains today, then into the
Central Plains tonight, and Northern Plains on Wednesday. The dryline
drifts into the Edwards Plateau this evening, stalling just west of
the I-35 corridor Wednesday. A strong capping inversion will inhibit
most convection today, except for some showers across the Escarpment
between San Antonio and Del Rio this morning due to moist upslope
flow there. As the upper level trough and a jet streak approach, the
cap breaks allowing showers and thunderstorms to form along the
dryline over Western Texas and over the Serranias del Burro of Mexico
this afternoon into early evening. These showers and thunderstorms
will organize into a line and move across the Edwards Plateau this
evening to the I-35 corridor by sunrise Wednesday morning. Convective
parameters of CAPE, shear, lapse rates indicate that some storms will
become strong to severe with large hail and damaging winds the main
threats. Have added this mention to the Edwards Plateau this evening
spreading to the remainder of the Hill Country overnight. Expect
showers and thunderstorms to weaken as they move further east as the
trough/jet move away allowing the capping inversion to restrengthen
Wednesday morning. Though, some showers and thunderstorms will linger
east of I-35 in the afternoon.

LONG TERM (Wednesday Night through Monday)...
An upper level trough currently approaching the Pacific Northwest
moves to near the Four Corners region on Thursday then out into the
Plains Friday into this weekend. The dryline drifting back to the
west combined with a mid level impulse will generate showers and
thunderstorms on Thursday. Convective parameters become favorable for
another round of strong to severe storms on Thursday. A weaker mid
level impulse and the dryline will generate showers and thunderstorms
on Friday. This weekend, a weak cold front drifts across our area
enhancing upward forcing and providing a focus for rainfall. This
focus will add locally heavy rains to our list of threats.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              70  88  75  89  73 /  50  40  10  20  40
Austin Bergstrom Intl Airport  70  86  74  89  73 /  50  40  10  20  30
New Braunfels Muni Airport     71  88  74  89  73 /  50  40  10  20  40
Burnet Muni Airport            68  87  71  87  70 /  60  20  10  30  40
Del Rio Intl Airport           69  94  70  94  74 /  30   0  10  20  30
Georgetown Muni Airport        69  87  73  88  72 /  50  40  10  20  40
Hondo Muni Airport             70  92  72  91  73 /  50  20  10  30  30
San Marcos Muni Airport        69  86  74  88  73 /  40  40  10  20  40
La Grange - Fayette Regional   71  84  75  89  74 /  20  40  10  20  20
San Antonio Intl Airport       71  89  74  90  74 /  50  30  10  20  40
Stinson Muni Airport           72  90  74  90  74 /  50  40  10  20  30

&&

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

$$

Mesoscale/Aviation...LH
Synoptic/Grids...24
Public Service/Data Collection...YB



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