Area Forecast Discussion
Issued by NWS San Angelo, TX
FXUS64 KSJT 031730
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1131 AM CST TUE DEC 3 2013
VFR conditions will prevail over the next 24 hours at all terminals.
Wind speeds of 10 to 15 knots, with gusts near 20 kts will likely
persist at all sites through sunset.
.PREV DISCUSSION... /ISSUED 420 AM CST TUE DEC 3 2013/
Today and tonight
Quasi-zonal flow aloft across the central CONUS will become a bit
more southwesterly over the next 24 hours as the potent shortwave
trough located over the PacNW digs slowly to the SSE. A strong,
dual upper-tropospheric jet pattern was analyzed on the 00z raob
data, with a 120kt jet streak extending from northern NV across the
central Rockies into the southern MO. Farther south, the second jet
streak (110kts) was found across the southern Rockies into the
middle TX coast. We`ll continue to see upper-level moisture spill
over the Rockies, providing scattered high clouds through the short
term. However, rain chances are basically nil as low-level dry air
will take some time to moisten.
The strong flow aloft will enhance the lee cyclone, which is progged
to dive south into the TX/OK Panhandles by this evening. This will
promote WSW surface winds today of 10-15 mph and an eastward
expansion of the 850mb thermal ridge. Temps at 850mb are progged to
warm 1.5C to 2.5C today, with a corresponding climb in surface temps
of 3-4 degrees Fahrenheit (from yesterday`s highs) based on a well
mixed boundary layer. This means most of West Central TX will warm
into the upper 70s to lower 80s today. This will likely remain well
below record values at Abilene and San Angelo, however. Tonight,
southwest winds will remain 5-10 mph with increasing high clouds.
We`ll also see a modest increase in surface dewpoints. These factors
point to mild overnight temps, with forecast lows in the upper 40s
to lower 50s.
As another cold front approaches from the north, temperatures will
remain warmer than normal. Surface winds will be southerly early
Wednesday morning; then, they will become more west for the
afternoon. Although West central Texas will have increasing clouds
on Wednesday, the westerly, down-slope, surface winds during the
afternoon should help offset the reduced sunshine. Thus, high on
Wednesday mainly in the mid 70s to around 80 range look good.
Wednesday night through Thursday night
Another strong cold front will bring very cold air and the potential
for a wintry precipitation mix. The NAM and GFS do not agree
regrading the timing of the front; the NAM is faster. Both models
indicate the front will move south to near our northern Big Country
counties late Wednesday afternoon or early Wednesday evening. Then,
the front stalls, before a good surge of surface cold air pushes it
to our Interstate 20 corridor by midnight. Again, this is the NAM
timing solution, and based on the last cold front, it looks best as
compared to the slower GFS. Rain chances begin with the front as it
sweeps south across our counties after midnight Wednesday night.
Rather than split hairs so-to-speak with PoPs, I decided to go with
20 PoPs across the board for Wednesday night. For Thursday and
Thursday night, the potential for a wintry precipitation mix still
looks reasonable. Forecast soundings, from the NAM and GFS, indicate
either freezing rain or sleet will be most likely, especially
overnight Thursday night, where likely PoPs look best. With models
this cycle presenting a relatively shallow moist layer aloft, I
don`t anticipate any significant accumulations of sleet or ice
Thursday or Thursday night at this time.
Friday through Monday
A wintry precipitation mix may linger Friday morning, otherwise,
look for slowly warming temperatures into the start of next week. As
the upper trough moves over West Central Texas Friday morning, model
soundings indicate either sleet or freezing rain may linger across
much of West Central Texas until around noon. Then, drier air aloft
begins to move into Texas. With either north or northeast surface
winds continuing through Saturday, I don`t expect much warming.
Plus, another upper trough slides across Texas this weekend. This
trough may bring additional precipitation on Saturday, with either
sleet or freezing rain the most likely precipitation modes. Again,
with precipitable water values relatively low, I don`t expect any
significant sleet or ice accumulations at this time. On Sunday,
southerly low-level flow finally returns and begins to bring some
surface warm air advection to West Central Texas. However, afternoon
highs Sunday and Monday will likely be mainly in the 40s - well
below seasonal normals. Don`t forget your coat!
.PRELIMINARY POINT TEMPS/POPS...
Abilene 79 52 74 34 38 / 0 0 5 20 50
San Angelo 82 50 78 44 47 / 0 0 5 20 40
Junction 83 50 80 49 54 / 0 0 10 20 40