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Forecast Discussion
000
FXUS64 KEWX 161129 AAA
AFDEWX
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
629 AM CDT Mon Sep 16 2019
.AVIATION...
/12Z TAFS/
VFR conditions are expected across area sites through late tonight.
Light and variable winds are expected through late this morning and
then becoming northeast to east around 5 to 10 knots for the afternoon
and evening with the exception of KDRT. A southeasterly wind flow of
5 to 10 knots is forecast for KDRT through the entire period.
Increased tropical moisture is forecast to arrive the Texas Coast
this afternoon and evening and continuing through Tuesday. MVFR
could occur by day break on Tuesday along the I-35 sites as
suggested by area forecast sounding. VFR cigs should return by late
Tuesday morning. However, scattered showers and thunderstorms are
expected for Tuesday afternoon and evening along and east of I-35
corridor. Some of these storms could produce lower cigs/vsbys in
addition to thunderstorm wind gusts up to 35 knots.
&&
.PREV DISCUSSION... /ISSUED 318 AM CDT Mon Sep 16 2019/
SHORT TERM (Today through Tonight)...
Mostly clear conditions prevail overnight across South-Central Texas
at the present time with just a few patches of mid-level clouds
moving from west to east. Dewpoints range from the low 60s in the
west to the low 70s in the east and the coolest lows overnight will
be in the west with the drier air that is in place.
Eyes for this forecast package continue to look to our southeast in
the Gulf of Mexico (GOM) at an upper level low that continues to
slowly meander around the northern GOM. This evening there was a good
mass of convection southeast of Houston, but warming cloud tops with
this feature indicate this convection is weakening. Latest
observations from Buoys around the GOM indicate east winds all
around the system which show that that there is no low-level low
associated with the mid and upper level feature. This goes well with
the latest Tropical Weather Outlook from the National Hurricane
Center that gives this system only a 10 percent chance of tropical
cyclone formation before the system moves over land.
For the short-term forecast, rain chances today and tonight will be
confined to the southeastern CWA in closer proximity to the feature
in the GOM. Although the higher concentration is expected closer to
the coast, an isolated shower could be possible farther to the north
and west. Rainfall amounts will average less than a tenth of an inch
through tonight with slightly higher values under the spots that see
some heavier convection. High temperatures today should continue to
be in the middle to upper 90s and will continue to go a couple of
degrees higher than guidance, sticking closer to persistence due to
dry soils. Lows tonight will be in the lower to middle 70s for most
locations.
LONG TERM (Tuesday through Sunday)...
The forecast for the rest of the work week will be highly dependent
on how the low over the GOM evolves through mid-week and where it
ultimately moves. Medium-range global models continue to have some
discrepancies with each other, even though they remain consistent
with their own solutions. The GFS and its ensembles continues to
slowly meander the low west before stalling it then dissipating the
low along the Texas coast by late this week. This solution also
keeps the low rather weak and therefore the bulk of the precip in
these solutions remain more confined to the coast. However, we would
still see some decent rain chances as scattered activity would be
possible mainly in the afternoons as diurnally driven convection
develops each afternoon through Friday as the low remains to our
southeast.
However, the ECMWF and now the Canadian/NAM, strengthen the mid-
level low with some reflection at the surface as it moves west
through tomorrow then SLOWLY moves the low north into the Texas
coast with a continued slow movement into North Texas by Friday. The
NAM/ECMWF/Canadian are all in fairly good agreement that the center
of the low will pass just east of our CWA Wednesday night into
Thursday. If this solution verifies this would likely mean our
eastern counties would be the most favored for possible heavy
rainfall with there likely being a sharp gradient in rainfall totals
due to a stronger upper level low and a defined backside to the
precip. Some of the run total rainfall accumulations from these
models are quite high for some areas to our east with 2-6 inch totals
shown for areas east of the I35 corridor.
For the official forecast, we will favor the consensus and show
likely PoPs for several periods for our eastern counties Tuesday
through Thursday and the upper low passes just to our east. Will
show decent chance PoPs for much of the remainder of the CWA, but
these could be a bit high if we do get the sharp edge in rainfall
amounts and future forecasts could show this gradient a bit better
in the PoP forecast if confidence in this solution increases. Latest
WPC QPF amounts through Friday show generally less than 3/4" for
areas west of the I35/37 corridors, 3/4" to 1" for the I35 corridor
and 1" to 4" for areas to the east of the I35 corridor. With
precipitable water values above 2 inches, which is quite high for
this time of the year, there will likely be isolated amounts higher
than these totals for any localized downpours that get sustained or
if we get any night time core rains from this system. It is quite
frankly too early to know any of these mesoscale details at this
time, but the potential is there. Some impacts from this system
could bring some localized flooding for locations which see the
heavier rainfall. In addition, this forecast is highly uncertain as
the ultimate track of the low will have a huge implication on
possible rainfall amounts for our area. Check back over the next 48
hours for possible changes to the forecast as models continue to get
a better handle on this system.
Most models agree that this low will be out of the area or weakened
by Friday afternoon and will just show some lingering chance PoPs
for Friday/Saturday afternoon and just some 20 PoPs on Sunday for
the eastern half as some residual moisture could bring some isolated
activity. Temperatures beyond today will be in the lower to middle
90s which will be an effect of the increased rain chances and cloud
cover. In addition, low temperatures should be a degree or two warmer
than what they have been with the increase in moisture over the
region.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 98 75 94 74 94 / 10 10 40 20 50
Austin Bergstrom Intl Airport 97 73 92 73 93 / 10 10 40 20 60
New Braunfels Muni Airport 97 73 92 73 93 / 20 10 40 20 50
Burnet Muni Airport 95 72 91 71 91 / 10 - 20 20 50
Del Rio Intl Airport 98 74 97 75 98 / 0 0 10 - 20
Georgetown Muni Airport 97 73 94 73 93 / - - 30 20 50
Hondo Muni Airport 97 73 94 73 97 / 10 10 30 20 40
San Marcos Muni Airport 97 73 92 72 92 / 20 10 40 20 60
La Grange - Fayette Regional 96 74 95 73 91 / 30 10 60 30 70
San Antonio Intl Airport 97 76 92 75 94 / 10 10 40 20 50
Stinson Muni Airport 96 76 92 75 93 / 20 10 40 20 50
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Aviation...17
Short-Term/Long-Term...Hampshire
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