Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Austin/San Antonio Texas
602 PM CST sun Dec 28 2014
Aviation.../00z taf cycle/
All sites are VFR and will be sky clear over the next couple hours. A
slight concern overnight will be some possible MVFR fog development
near ksat/kssf and kdrt 10z through 15z. Calm winds combined with
ideal radiational cooling conditions overnight will allow for the
boundary layer to cool substantially. Hrrr output and nambufr/rap
soundings point towards patchy fog development along with some hints
in the gfslamp and nam12 visibility guidance. Have trended
ksat/kssf/kdrt toward gfslamp guidance for now and will monitor
updated guidance for 06z issuance if IFR conditions appear possible.
Previous discussion... /issued 335 PM CST sun Dec 28 2014/
Short term (tonight through Monday night)...
an upper level trough is exiting to the east of south central
Texas this afternoon. Skies have cleared to near I-35. Skies will
clear across the remainder of our area by sunset. This sets the
stage for widespread freezing temperatures by Monday morning. We
have issued a freeze warning for late tonight into Monday morning
for our southern two tiers of counties...except for the southwest.
These areas have not yet reached freezing this fall/winter.
Meanwhile...The Hill Country and along the Escarpment already have
seen freezing temperatures this winter season while the Rio Grande
plains will fall to just above freezing. See our Special Weather
Statement for details for those areas. A brief warm up is expected
on Monday on south to southwest winds. Late Monday night another
cold front is expected to enter the far northern Hill Country.
Temperatures should stay above freezing Monday night on mixing
along and ahead of front.
Long term (tuesday through sunday)...
the cold front will surge across the remainder of south central
Texas Tuesday morning. High temperatures will be reached late
morning to midday as clouds increase due to moist southerly flow
riding over cold advection in the lower levels. Models are in
better agreement on the pattern evolution in the long term.
Although...some disagreement remains and the forecast may change
over the next few days. An upper upper level trough dropping down
the West Coast on Tuesday closes off over Southern California on
Wednesday into Thursday and then opens up and move across Texas
Friday into early Saturday. Isentropic lift develops Tuesday night
into Wednesday leading to areas of light rain initially along the
Rio Grande...then spreading across the remainder of the area.
Periods of light to occasionally moderate rain or showers will
continue through Friday night. There is a threat for winter type
precipitation during the late night into morning hours mainly for
parts of The Hill Country Tuesday night through Thursday (new
years day) morning. Forecast soundings show a thick layer above
freezing developing on top of a shallow subfreezing boundary
layer. Freezing rain is the likely winter type precipitation that
is expected where temperatures drop below freezing. However...no
significant ice accumulations are expected. Should the rain become
more convective...then some sleet may be possible over a greater
area. Finally...there may be a threat of light snow across western
Edwards Plateau prior to the development of the warm layer aloft.
By Thursday afternoon...the lower levels warm above freezing with
only a cold rain expected. As the upper low approaches and moves
across...some thunderstorms are possible due to elevated
instability Thursday night through Friday night. The rains end from
west to east by Saturday morning. Fair skies and much warmer
daytime temperatures are expected next weekend.
Preliminary point temps/pops...
Austin Camp Mabry 32 61 39 46 36 / 0 0 - 10 10
Austin Bergstrom international Airport 25 60 35 46 36 / 0 0 - 10 10
New Braunfels Muni Airport 29 61 36 48 38 / 0 0 - 10 10
Burnet Muni Airport 30 61 36 43 32 / 0 0 - 10 20
del Rio International Airport 33 62 40 56 37 / 0 0 - 10 30
Georgetown Muni Airport 28 60 35 44 34 / 0 0 - 10 10
Hondo Muni Airport 28 62 35 51 38 / 0 0 - 10 20
San Marcos Muni Airport 29 61 36 47 37 / 0 0 - 10 10
La Grange - Fayette regional 31 59 40 50 39 / 0 0 - 10 10
San Antonio International Airport 32 62 39 49 38 / 0 0 - 10 20
Stinson Muni Airport 32 61 39 51 39 / 0 0 - 10 20
freeze warning from 2 am to 9 am CST Monday for the following
counties: Atascosa...Delaware Witt...Fayette...frio...Gonzales...Karnes...
public service/data collection...33