381 
fxus64 khgx 212309 
afdhgx 


Area forecast discussion 
National Weather Service Houston/Galveston Texas 
509 PM CST Sat Nov 21 2009 


Discussion... 
see aviation discussion below. 


&& 


Aviation... 
a complicated taf package this evening. Clearing line is 
tantalizingly close and feel ceilings will lift briefly during the 
middle-evening before lowering again after 06z. Wet ground coupled 
with the brief clearing will lead to fog and lower ceilings developing. 
Winds will remain light overnight. Skies will clear by 15z across 
southeast Texas with VFR conditions prevailing through 00z. 43 


&& 


Previous discussion... /issued 400 PM CST Sat Nov 21 2009/ 


Discussion... 
surface low located along the SW Louisiana coast with upper low 
beginning to lift out of southeast Texas. Precipitation has mostly come to an end 
at this point with subsident airmass on back side of low beginning 
to spread into the area. Finally seeing some breaks in the clouds 
over the western zones. Have leaned toward more conservative NAM 
with the cloud forecast...keeping the low clouds in place over the 
eastern half through most of the evening. Skies should clear area 
wide by late tonight. The clearing skies along with light winds 
and wet ground conditions should set the stage for fog development 
during the late night/early morning hours. Once fog Burns off by 
middle morning Sunday will be a very nice day with lots of sunshine 
and maximum temperatures in the upper 60s/lower 70s. Light onshore flow will 
develop late Sunday as weak surface high moves east. The increasing 
dewpoints and light southeasterly flow will set up even more 
favorable conditions for fog development Sun night/early Monday. 
Longwave upper trough is forecast to develop across the plains 
Monday. The associated cold front will push across southeast Texas 
Tuesday. Moisture return ahead of the front is expected to be 
fairly modest as low level jet never becomes fully established. 
Flow aloft becomes diffluent Monday night...but best jet dynamics 
stay north of the area. Still...precipitable waters  are expected to increase to 
1.1-1.4 inches late Monday night/early Tuesday. The increasing 
moisture along with convergence along the front will aid in 
development of scattered -shra Monday night...and a narrow band of 
convection along the front Tuesday. Have gone with chance probability of precipitation 
late Monday night/Tuesday. Kept probability of precipitation going through Tuesday afternoon with 
European model (ecmwf)/NAM showing a somewhat slower frontal movement than the GFS. 
Rapid clearing is expected Tuesday night as front clears the coastal 
waters. 


Deep troughing develops over the eastern states beginning 
Wednesday. Surface high settles over southeast Texas Wednesday and gets 
reinforced going into the weekend as a couple of additional fronts 
pass through in the northwest flow aloft. The end result should be 
very nice weather for the Thanksgiving Holiday...dry and cool with 
lots of sunshine. Expect min temperatures in the 40s...maximum temperatures in the 
60s for most of the County Warning Area Wednesday through Friday. Onshore flow 
develops Saturday as the next longwave trough develops over The 
Rockies. Expect a gradual increase in cloudiness and moisture 
levels over the weekend...with rain chances possibly back in the 
forecast as early as Sunday. 


35 


Aviation... 
looks like fog may be an issue tonight as the wet grounds...calming 
winds and clearing skies come into play overnight. Not seeing a lot 
of significantly drier air moving into the the area behind the exit- 
ing storm system per current obs/trends. As such the IFR ceilings/visibilities 
currently in the tafs may not be low enough and LIFR conditions may 
be widespread by sunrise Sunday. 41 


Marine... 
looks like things are improving this afternoon. Winds/seas continuing to 
slowly fall as the low moves off to the east-northeast. Will go ahead and drop 
the Small Craft Advisory for our coastal waters and go with an scec through the next 
update/package. Light offshore winds until Sun night. The return of 
light onshore winds to be fairly brief as the next cold front moves 
into the area on Tuesday. Small Craft Advisory conditions are prognosticated behind this front 
from Tuesday night through Wednesday afternoon. 41 


&& 


Preliminary point temps/pops... 
College Station (cll) 48 70 48 75 56 / 10 0 0 10 30 
Houston (iah) 48 70 48 76 61 / 10 0 0 10 30 
Galveston (gls) 53 66 55 73 64 / 10 0 0 10 30 


&& 


Hgx watches/warnings/advisories... 
Texas...none. 
GM...small craft should exercise caution until 9 PM CST this evening 
for the following zones: waters from Freeport to the 
Matagorda Ship Channel 20 nm to 60 nm...waters from 
Freeport to the Matagorda Ship Channel out 20 nm...waters 
from High Island to Freeport 20 to 60 nm...waters from High 
Island to Freeport out 20 nm. 


&& 


$$ 


Discussion...39 
aviation/marine...43