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

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FXUS64 KEWX 221637

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1037 AM CST Thu Feb 22 2018

There are still some isolated light rain showers around the area. New
models continue to show this activity through the afternoon. We will
leave the forecast alone for the rest of the day. We should see
isolated showers across the eastern half of the CWA and most of them
will only produce light rain. The rest of the area will be mostly
cloudy, but dry. We have adjusted the hourly grids to account for
observational trends.


.PREV DISCUSSION... /ISSUED 526 AM CST Thu Feb 22 2018/

KAUS, KSAT, KSSF will remain IFR/LIFR today through Friday morning
with intermittent -SHRA mainly this morning and a more steady -RA
overnight into Friday morning. ISOLD TSRA are possible, however,
PROBS less than 30. N to NE winds of 5 to 10 KTs today decrease to
around 5 KTs tonight. KDRT will slowly rise from IFR to MVFR this
afternoon. Some models suggest even clouds becoming SCT for a time
late this afternoon into evening, however, for now will go with BKN
MVFR CIGs. N winds around 5 KTs become E this afternoon.

PREV DISCUSSION... /ISSUED 418 AM CST Thu Feb 22 2018/

SHORT TERM (Today through Friday)...
As of 330AM, isolated to scattered showers were developing across
much of the CWA and temperatures ranged from around freezing in the
northernmost parts of Burnet, Williamson, Edwards, Gillespie, and
Llano counties. Some low lying areas measured by LCRA temperature
gauges have dipped into the upper 20s in these areas as well.

The primary concern is in the pre-1st period this morning as these
freezing or below temperatures interact with the light showers
developing. Just about all guidance keep the current temperatures
steady through the rest of the early morning hours. Looking at
dewpoint temperatures, almost all sites show 1-2 degrees of dewpoint
depression and with CAA pretty much halted now with calm or very
light north winds, don`t think these temperatures will be able to
fall much, if any. Also of consideration is the very shallow nature
of the cold air in place. Even if surface temperatures are able to
reach freezing, RAP soundings indicate temperatures at 1000ft around
40 degrees. So while freezing rain is still very much possible, it
will likely only be able to exist as freezing rain with the lightest
precip. The more significant rain producing showers will likely serve
to pull down this much warmer air, or the precip itself will be
considerably warmer than the surface and wont have enough residence
time to even become supercooled. Thus, while freezing rain chances
are not non-zero, still don`t believe this will result in anything
significant for the Hill Country other than low lying areas that are
a few degrees cooler seeing a light glaze, if anything at all.

Temperatures will begin rising slowly shortly after 12Z and eliminate
any freezing rain possibilities but shower activity should be
prevalent through about 18Z as overrunning and a weak UL disturbance
interact, but as that disturbance shifts northeast, so will the
shower activity. Thus have tempered down PoP chances after 18Z today
for the eastern 2/3 of the CWA and removed PoPs entirely for the
western third.

Models have been ramping up QPF with the next H5 shortwave overnight
tonight into tomorrow morning, both in the synoptic and hi-res model
suite. A strengthening low level jet will push the 850 mb front back
to the north providing a focus for convergence as the shortwave
passes over. As these features come into phase initially between 06Z
and 12Z Friday morning, so will PoP chances. However, QPF should be
maximized north and east of the CWA, closer to the where the 850 mb
front sets up over north Texas.

LONG TERM (Friday Night through Wednesday)...
Our next frontal system will arrive from the west on Saturday and
bring westerly winds and much drier air into the region Saturday
afternoon. Some initial precip associated with the frontal passage is
expected but behind the front, RH values are expected to drop
considerably with gusty winds of up to 25 mph in the afternoon. Many
will likely welcome this as this will finally bring some sunshine to
the region for the latter half of the weekend with temperatures in
the 60s/70s.

Towards the end of the extended, Tuesday evening, we will begin to
see effects of the next trough positioned on the windward side of the
Rockies. GFS/ECMWF/Canadian all generally agree on PoPs increasing
Tuesday but how long we will be effected by the trough is in question
as the GFS lifts this feature quickly northeast by Wednesday night
but the other two keep a closed low just to the west of the Four
Corners region. Thus confidence is low for details beyond Tuesday.


Austin Camp Mabry              47  45  69  61  73 /  70  70  60  40  60
Austin Bergstrom Intl Airport  47  45  70  62  72 /  70  70  50  40  60
New Braunfels Muni Airport     50  47  70  62  74 /  60  70  50  40  50
Burnet Muni Airport            44  43  64  57  70 /  70  70  70  50  60
Del Rio Intl Airport           57  51  69  57  75 /  30  30  30  30  10
Georgetown Muni Airport        45  43  66  60  71 /  70  70  70  40  60
Hondo Muni Airport             53  50  70  61  76 /  50  60  60  40  30
San Marcos Muni Airport        48  45  71  62  73 /  70  70  50  40  50
La Grange - Fayette Regional   51  49  75  65  74 /  60  70  40  30  60
San Antonio Intl Airport       51  48  70  62  74 /  60  70  50  40  50
Stinson Muni Airport           52  48  72  63  76 /  60  70  40  40  40




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