084 
fxus64 khun 211147 aaa 
afdhun 


Area forecast discussion...updated 
National Weather Service Huntsville Alabama 
547 am CST Sat Nov 21 2009 


Update... 
for 12z aviation. 


&& 


Aviation... 
cirrus canopy will gradually lower/thicken as a low pressure 
system approaches from the SW. Very dry air in the low-levels will 
likely prevent precipitation at terminals until after 22/00z. Primarily light 
rain with VFR conditions are anticipated between 06z and 12z. 
However...MVFR visible may occur toward the end of the taf period if 
MDT rain develops earlier than expected. 


&& 


Discussion... /issued 215 am CST Sat Nov 21 2009/ 


Short term (today through monday)... 
as expected...high clouds have spread across the area...and this 
sets the stage for not the nicest of weekends. However...it looks 
increasingly likely that today will not be bad...just with not a 
lot of sunshine. Temperatures today will in fact be rather 
mild...reaching the lower and perhaps middle 60s. Rain is looking 
less and less likely today with soundings showing almost all the 
moisture above 10 kft... except south and west late this 
afternoon. Will remove the slight chance of showers. 
However...some precipitation off to the west in Arkansas is reaching the 
ground in trace amounts...even out of the 10 kft ceilings. So will 
carry a slight chance of a sprinkle this afternoon. 


Models have lost their way regarding the approaching Gulf coastal 
system...with plenty of model disagreement. The GFS and its 
ensembles are favoring an even more southerly/easterly movement than 
before...leaving parts of the area almost completely dry. This is a 
total flip from prior runs. The NAM is more consistent but also much 
slower to bring in precipitation...not until late tonight or even Sunday. 
Will be cutting back probability of precipitation except in the southern counties...and 
focusing on the after midnight period. Despite cutting probability of precipitation...I 
remain Above All the model guidance probability of precipitation. With clouds and moisture 
in place...lows should remain around 50. 


Upper low comes across...in some form...on Sunday. GFS is too fast 
with that movement and will not be followed. In general...Sunday 
looks cloudy...raw...breezy...and with a good chance of rain. Given 
that the system will be weakening...uncertainty abounds. Will again 
hold probability of precipitation steady in the east and taper them lower to the northwest. 
Temperatures will hardly move...staying at best in the middle 50s. Although 
the system dissipates Sunday night...there is no frontal passage...and thus no 
airmass change. Meanwhile...models show a northern stream upper wave 
coming across. Soundings look quite favorable for low clouds and 
drizzle...perhaps even a light shower. Will keep the mention of 
slight chance rain or drizzle Sunday night...and expand it through 
Monday morning in the eastern counties. Some breaks in the clouds 
are possible Monday afternoon...so highs may approach 60. 


Extended (monday night through next saturday)... 
the rest of the forecast is quiet...despite the pattern being 
active. An approaching northern stream cold front is forecast to move 
through sometime Tuesday /or maybe Tuesday night/. Not a lot of 
forcing...but frontal forcing may spark a shower or two in the 
vicinity of the front. Will keep a slight chance mention on Tuesday 
afternoon everywhere...and in the east only Tuesday evening. 


This Ushers in cooler temperatures for Wednesday...which are 
reinforced by a stronger dry cold front Wednesday night. By the 
way...the European model (ecmwf) remains about a day slower with both of these fronts 
and for now...it is not being followed. Thanksgiving and the day 
after look dry but rather chilly...with highs 50 to 55 and lows 30 
to 35. A bit of a warmup looks possible to start next weekend...but 
it may not last long with another front currently shown late next 
weekend. 


&& 


Hun watches/warnings/advisories... 
Alabama...none. 
Tennessee...none. 
&& 


$$ 


Aviation...kdw 
discussion...je/23