111 
fxus63 klsx 082059 
afdlsx 


Area forecast discussion 
National Weather Service St Louis MO 
259 PM CST Thursday Jan 8 2009 


Discussion... 
/259 PM CST Thursday Jan 8 2009/ 


Surface high pressure centered across the County Warning Area early this evening 
will allow temperatures to drop off quite quickly before warm 
advection kicks into gear later tonight. Have once again undercut 
numerical guidance and have a non-diurnal trend in temperatures 
depicted in the gridded database. 


Temperatures still expected to warm into the 50s tomorrow with an 
increasing south to southwest wind ahead of an approaching cold 
front. Southwest downslope favored locations like kjef and ksus may 
flirt with 60 degrees. 


Cold front will be knocking on our western County Warning Area at 00z. Have kept the 
trend of highest probability of precipitation across the southeastern half of the County Warning Area where 
the majority of the guidance has measurable quantitative precipitation forecast ahead of the front. 
Not much Post-frontal precipitation expected...perhaps a little 
light snow across our northern two tiers of counties on the tail 
end of the deformation zone. 


Temperatures will remain quite chilly on Saturday with cloud cover 
and a few flurries around. Clouds should scatter from west to east 
late in the day as weak high pressure builds across the County Warning Area. 
Temperatures will moderate through the remainder of the weekend as 
the high departs and return flow ensues. 


Extended... 


1055mb high pressure center will drop south from the Arctic... 
arriving right on schedule...the coldest time of the year 
according to climatology. Have leaned heavily toward the coldest 
ensemble guidance members for temperatures...which are closer to 
the operational 2 meter temperatures of the ecwmf and GFS. The 
deep Arctic cold that has been building for weeks to our north is 
coming south next week folks. It promises to bring the Midwest the 
coldest air of the season and likely the coldest air we have seen 
in St. Louis for more than 10 years. The last time St. Louis 
dropped below zero was January 5th 1999...when the low was -5f. 


True Alberta clipper dives southeast across the Midwest on Monday 
with the typical band of advisory type accumulating snow occurring 
north and east of the middle-level vorticity track. Have introduced 
chance probability of precipitation across northeast half of the County Warning Area given continuity 
between latest GFS and ecwmf solutions. 


Temporary high pressure moves across forecast area Monday night and 
Tuesday morning...before warm advection kicks in Tuesday evening 
ahead of the next clipper and Arctic cold front. Have only 
introduced slight chance probability of precipitation in forecast for this second clipper 
given uncertainty of eventual track of this feature. Large Arctic 
high builds across the County Warning Area through Friday morning...with very cold 
temperatures. We could certainly see temperatures dropping below 
zero Friday morning...especially where fresh snow cover exists. 


This cold has staying power...as another +1050mb high pressure 
center is prognosticated to drop south late next weekend (january 
18-19)...which will continue to keep the Midwest in a deep freeze. 


Cvking 


&& 


Aviation... 
/1108 am CST Thursday Jan 8 2009/ 
for the 18z tafs... 


High pressure centered through the Mississippi Valley region will 
gradually move eastward this afternoon and tonight with warm air advection 
ensuing on the backside. Warm air advection aloft already is producing a band of middle 
clouds streaming southeastward into eastern Kansas and northwest MO. These should progress 
eastward as well and March across the County Warning Area in association with the 
developing warm air advection regime. Expecting any ceilings to remain in the VFR 
Cat. Southerly low level flow will become established by early 
Friday as the high continues to retreat and a new storm system gets 
organized over the central U.S. Increasing southerly flow 
throughout the day is expected to lead to stratus advecting from 
the lower MS valley into southern MO during the afternoon. 


Glass 


&& 


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


$$ 


Weather forecast office lsx