Area Forecast Discussion
Issued by NWS San Angelo, TX
FXUS64 KSJT 090500
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN ANGELO TX
1100 PM CST SUN DEC 8 2013
Areas of dense fog over Central TX continue to build back to the
west this evening and are right on the CWA border near San Saba and
Brownwood. Given extremely low dewpoint depressions, a general east
to southeast flow, and some residual sleet/ice pack on the ground, I
expect this westward trend to continue. BUFKIT hydrolapse analysis
of the NAM and RAP data indicate support this conceptual model.
Thus, I have issued a Freezing Fog Advisory for areas along and east
of a Baird, to Coleman, to Brady through 9 AM Monday. Visibilities
are already down to 1/4 mile at Lampasas and Hamilton and RH values
at Brownwood and Brady are greater than 93% currently. Given
sub-freezing temperatures, any areas of dense fog will likely result
in light ice accumulations on exposed surfaces. For aviation
impacts, see the aviation section below.
The remainder of the forecast package was in good shape. Minor
changes were made to overnight temperatures, with lows across the
Big Country increased by just a few degrees.
The forecast terminals will begin to the period with benign
conditions but I expected patchy freezing fog to develop overnight
across West Central TX. At this time, the greatest threat appears
to exist from KBWD to KBBD, but freezing fog will be possible at all
terminals later tonight. Visibilities are the lowest at KBBD with
only minor reductions forecast for the remaining forecast terminals.
In addition to the fog, an arctic cold front will move south across
West Central TX overnight, resulting in north to northeast winds of
8-12 kts and low ceilings. IFR ceilings are expected to develop late
tonight and persist through midday, gradually improving into MVFR
range during the afternoon and evening hours. Patchy, post-frontal
freezing drizzle is a concern but low confidence does not warrant a
mention in the current forecast package.
.PREV DISCUSSION... /ISSUED 540 PM CST SUN DEC 8 2013/
Another shallow arctic cold front will move through West Central TX
late tonight and early Monday. Ahead of the cold front, we`ll see
light winds, generally from the south, under clear skies.
Sublimation over the sleet/ice pack will promote the development of
patchy fog (and freezing fog) tonight. Enough spatial uncertainty
exists that it extremely low visibilities will not be included in
the current TAF package. I did, however, reduce visibilities to 3-5
statute miles in most areas, but amendments may be required in areas
where fog does form as the forecast is likely too optimistic. Some
of this fog may lift into an IFR stratus deck as well.
As the front moves through the area, winds will shift to the north
at 8-10 kts and stratus is expected to become more widespread. I
would not rule out some patchy, post-frontal freezing drizzle.
Again, however, the relatively low probability does not warrant
mention in the TAF. I expect slow improvement in ceiling heights on
Monday afternoon as the cold air deepens and lift over the frontal
PREV DISCUSSION... /ISSUED 355 PM CST SUN DEC 8 2013/
Tonight and Monday
Patchy freezing fog tonight and Arctic air Monday
Clearing skies and light winds may allow the development of patchy
freezing fog. This may potentially bring icing to bridges and
overpasses, mainly after midnight, as temperatures fall to the dew
point. Sleet from last week has been finally melting, with the
visible satellite imagery still indicating sleet on the ground from
the Big Country southward to San Angelo, Brady, and Brownwood. The
sleet will help moisten the boundary level tonight, further enhancing
the potential for fog.
An arctic cold front will move into the Big country, moving through
the I-20 corridor around 3 AM, and I-10 corridor around 9 AM. Low
level cloud development and mixing should dissipate the fog as the
arctic front moves through. Temperatures in the Big Country will
likely stay in the 20s Monday with wind chills in the single digits
in the morning. People should dress accordingly.
Monday Night through Sunday
Cold temperatures will continue Monday night and Tuesday with a
warming trend Wednesday through next weekend. A short wave trough
will move across the Southern Plains Monday night with surface high
pressure settling into the area into Tuesday. Temperatures will be
very cold Monday night with overnight lows falling into the upper
teens and lower 20s. The cold surface high will be overhead on
Tuesday and despite some sunshine, temperatures will remain well
below normal with afternoon highs ranging from the upper 30s along
and north of the I-20 corridor, to the lower 40s along the I-10
By Wednesday, a broad upper level trough will cover much of the
country with a weak upper low developing over the Baja region.
A weak cold front will move across the area again on Wednesday
but the associated surface high and coldest airmass will remain
well northeast of the area through Thursday. Temperatures both
Wednesday and Thursday will continue to be well below normal but
will at least warm into the mid and upper 40s during the afternoon
hours, with a few low 50s possible along the I-10 corridor.
Southerly flow and increasing moisture return Thursday night and
Friday ahead of the approaching upper low over the Desert Southwest.
This system will bring a low chance of rainfall to mainly eastern
sections Thursday night and early Friday. Models show another upper
level trough and possible front affecting the area over the weekend
but this system looks dry. Expect warmer temperature Friday through
Sunday with highs in the 50s and lows in the 30s.
.PRELIMINARY POINT TEMPS/POPS...
Abilene 20 28 17 38 24 / 0 5 5 0 5
San Angelo 25 37 20 43 24 / 0 5 5 5 5
Junction 28 45 23 45 24 / 5 10 10 5 5
FREEZING FOG ADVISORY until 9 AM CST Monday FOR THE FOLLOWING
ZONES: Brown...Callahan...Coleman...McCulloch...San Saba.