773 
fxus63 klsx 091216 
afdlsx 


Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
616 am CST Friday Jan 9 2009 


Discussion... 
/352 am CST Friday Jan 9 2009/ 
active weather regime in store for the central U.S. Over the next week or 
so...as the upper air pattern transitions to a deep long wave trough over the east Continental U.S. 
By the end of next week. A series of shtwv troughs are forecast to zip acr 
our area in the increasingly energetic northwest flow....the first 
tonight...the second on Monday...and a third by middle week. Warm air advection/cold air advection pattern 
with each of these systems will be causing fairly large day to day 
temperature changes...as strong baroclinic zn wobbles back and forth acr area. 


It certainly aprs that today will be the warmest day in the near 
future....as warm air over plains attempts to surge east ahead of surface low 
and cold front. Warm front has worked itno west MO early today...and the hi res 
WRF/NAM...RUC...and local WRF all suggest that it will be near a 
Moberly...ppq line by late in the day. This should result in a very strong 
temperature gradient acr north part of forecast area...with a 15 degree temperature difference 
expected between uin and jef. Going forecasts...which have temperatures pushing 
into the lower 60s in sm parts of middle MO...still lakes very good. 


Although the day will begin with lots of sunshine...low level moisture advection will 
spread into the area during the afternoon. SC deck developing in this plume of 
moisture has grown nicely acr East Texas during the predawn hours...and these clouds 
should ovrsprd our area during the lt afternoon hours. This moisture should also 
set the stage for precipitation during the night as the dynamics with the trough 
works into the area. With the 00z data indicating a slower eastward 
progression of the system have upped probability of precipitation entire area for tonight...and in 
the east on Sat morning. The progressive nature of the trough should allow 
the southward surge of the cold air to be fairly deep...which means the 
transition from rain to snow should be fairly quick. Its certainly 
possible there culd be a bit of mixed precipitation...but because of above 
reasoning think this wuld be quite brief. 


The first of several cold air intrusions will occur on Sat as the system 
works east. Strong cold air advection and cloud cover should minimize wrmup during the 
afternoon...and have only allowed maximum temperatures about a 5 degree rebound from early 
morning mins. 


The remainder of the pkg follows going forecast trends...with moderating 
temperatures on sun...followed by a shot of snow with a clipper on 
Monday...with another brief moderation on Tuesday...followed by more cold 
air behind the next clipper on Wednesday. The primary question is which 
system will truly tap the Arctic air lurking to our north and send it our 
way. Although I did not alter temperature forecasts...it could be that we are 
emphasizing the cold air too much/too fast behind Mons system...and 
Tuesday may be a bit warmer due than going forecasts to rapid return of warm advection 
ahead of the midweek clipper. However...GFS and European model (ecmwf) output certainly 
makes it Apr that we will be well in the grasp of the Arctic 
outbreak for the last few days of next week...with the broad 
shouldered 1045-1055mb hi prognosticated into area. 


Truett 


&& 


Aviation... 
/551 am CST Friday Jan 9 2009/ 
for the 12z tafs...S-sely surface winds will strengthen and become gusty 
later today as the surface ridge east of the County Warning Area continues to shift further eastward and 
a cold front approaches from the plains. Do not see much clouds for most 
of the day except some cirrus clouds...but low level clouds across eastern 
Texas should eventually spread north-northeastward into the County Warning Area lt this afternoon. Rain 
should break out this evening as this low level moisture intercepts 
the southeastward dropping cold front which will pass through uin lt this 
afternoon...cou early this evening...and stl/sus by lt evening. Strong and gusty 
north-northwesterly surface winds can be expected behind this fnt. As the temperature falls 
the rain will change over to light snow during the lt evening in uin 
and during the lt night hours in cou...stl and sus. The cloud ceiling 
should lower to around 1000 feet by lt tgt as the models are forecasting plenty 
of low level Post frontal moisture. 


Gks 


&& 


Climate... 
last time low temperatures dropped below zero 


Stl...Jan 5 1999 -5 
cou...Feb 16 2007 -1 
uin...Dec 22 2008 -2 


&& 


Lsx watches/warnings/advisories... 
MO...none. 
Illinois...none. 
&& 


$$ 


Weather forecast office lsx