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

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FXUS64 KEWX 190916

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
416 AM CDT Mon Jun 19 2017

.SHORT TERM (Today through Tuesday)...
South Central Texas remains in northerly flow aloft between an upper
level ridge of high pressure centered near the Four Corners region
and a weak trough/shear axis along the Mississippi River Valley into
the western Gulf of Mexico. A weak front stretching from Ozona to
Denton into far southeast Oklahoma has triggered some showers and
thunderstorms in the Red River Valley. Hi-res and global models
continue to show that these storms will progress to the S-SE before
traveling a bit more to the S-SW as they cross the ridge axis south
of the Interstate 20 corridor. Although aircraft and model soundings
both show a strong capping inversion at the top of the boundary
layer, some of this convection may slip into our northern counties
late this morning. Isolated showers and thunderstorms may redevelop
later this afternoon as temperatures warm up into (just) the mid 90s
with assistance from the weak and dissipating front and/or outflow
boundaries to help erode a weakening cap. Thus, 20 POPs have been
included mainly along and north of Interstate 10, but this may have
to be expanded further south and west if other models trend towards
the last few HRRR runs that reintensify convection over the higher
terrain of the Hill Country later this afternoon. Pulse severe storms
capable of brief strong wind gusts will be possible in this scenario
given the inverted V profile seen in SJT`s model soundings, but for
now SPC has the marginal risk just to the north of our CWA in
alignment with the broader model consensus.

Shower and thunderstorm activity may linger over the Hill Country and
Edwards Plateau into the evening hours before setting up a quiet and
slightly cooler night over the region. The mid-to-upper ridge is
expected to reintensify over eastern Arizona tomorrow to help rebuild
the ridge axis over northern Texas, causing high temperatures to
increase a few degrees back into the upper 90s. However, relative
humidity values will be lower than they have been the past few days
to keep heat indices closer to 100. Both the ECMWF and GFS show some
light QPF in the Coastal Plains, but the increased ridging should
make it difficult to move beyond a strengthening cap at midlevels.
Thus, for now have just kept in a silent 10 POP for Tuesday afternoon
across most of the region which will only need to increase if this
weak dissipating front and any of its associated convection breaks
down the ridge more than models currently show.


.LONG TERM (Tuesday Night through Sunday)...
The forecast beyond Tuesday is relatively uncertain and dependent
on what becomes of a disorganized area of showers and thunderstorms
along and just east of the Yucatan Peninsula. These storms are
associated with an inverted trough and/or shear axis that is forecast
to move northwest into the Gulf today, which the NHC gives an 80
percent chance of tropical cyclone formation within 48 hours. There
is still significant uncertainty on when and where a tropical cyclone
might develop given relatively strong shear aloft and the broad
nature of the trough, but the model spread should decrease once we
are able to sample a closed circulation in the Gulf. Nevertheless,
models appear to be trending towards this system moving into the
weakness east of the subtropical ridge as opposed to moving due west
along the southern periphery of the ridge into Mexico or south Texas.
Where this weakness will set up definitively is still a challenge
and will be dependent on how much today`s weak front helps weaken the
ridge and how much it is able to rebuild on Tuesday. For now, we have
continued 20 POPs for the Coastal Plains to account for the model
uncertainty with whatever tropical system develops. The rest of the
region has been kept dry given weak ridging and dry northerly flow
aloft west of whatever tropical system develops with temperatures
climbing back into the upper 90s and possibly lower 100s for the
second half of the week. The ECMWF ensemble MOS guidance is also
trending towards warmer temperatures and dry weather despite being at
the western end of most model guidance. Please stay tuned over the
next few days for updates on the this Gulf tropical system.

Finally, global model consensus continues to show a weak front
moving through the region for the second half of next weekend. This
would bring increased rain chances and a brief stint of cooler than
normal temperatures to the region. Although this would be a welcome
change moving into late June and early July given the hot and dry
weather we have seen the past few weeks, muted optimism is probably
best considering weak fronts only make it into South Central Texas
1-2 times each summer on average.


Austin Camp Mabry              95  76  97  73  98 /  20  10  10  -   -
Austin Bergstrom Intl Airport  94  73  96  71  97 /  20  10  10  -   -
New Braunfels Muni Airport     94  75  96  72  97 /  20  10  10  -   -
Burnet Muni Airport            92  72  93  70  95 /  20  20  10   0  -
Del Rio Intl Airport           98  77  99  74 102 /  -   10  10   0  -
Georgetown Muni Airport        93  72  94  70  96 /  20  20  -   -   -
Hondo Muni Airport             97  75  97  71 100 /  -   10  10  -   -
San Marcos Muni Airport        94  75  96  70  97 /  20  10  10  -   -
La Grange - Fayette Regional   94  75  96  73  95 /  20  10  10  10  10
San Antonio Intl Airport       95  77  96  73  99 /  10  10  10  -   -
Stinson Muni Airport           95  77  96  74  99 /  10  10  10  10  10




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