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fxus63 klsx 071730 
afdlsx 


Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
1130 am CST Wednesday Jan 7 2009 


Discussion... 
/506 am CST Wednesday Jan 7 2009/ 
are between system this morning with upper air trough over cntl MO. This trough will continue 
to slowly move eastward today. As it does...short wave currently over the Dakotas 
will drop S and bring a chance of snow this evening. Expect flurries today area 
of low clouds moving S through the County Warning Area. 


Precipitation chances will increase late afternoon and evening and be the focus in the 
near term. Baroclinic zone drops S through the County Warning Area late this afternoon and 
evening as short wave begins to round the base of the upper air trough. Models differ on 
how fast this fnt will move through the area...which results in a large 
temperature diff in MOS guide for today. The GFS is slower...with the 
NAM/UKMET/ECMWF having a faster solution. 


Models indicate good forcing available tonight. Ulj off to the northwest will put 
the County Warning Area under the poleward-exit region. Low level frontogenesis should 
set up and provide enough forcing for snow...mainly through the middle of 
the County Warning Area. Amnts will be a tough call...but have started with around a 
half inch for eastern MO and SW Illinois. 


Have trended toward the colder MOS for today. Will be in much the same flow 
as yesterday with neutral advection near the surface. Focus then shifts to 
temperatures for Thursday. Surface will build into the region with northerly flow over the 
County Warning Area through at least 18z. Winds should become southerly across western portions of the 
County Warning Area before 00z...with temperatures raising again during the night. 


Friday is experimental to be the warm day in the forecast period. Strong southerly surface flow 
present with SW low level jet should help warm temperatures into the upper 40s to middle 50s 
across the County Warning Area as another system approaches the area. Experimental rain showers/rain to develop 
Friday evening as cold front approaches the County Warning Area. P-type becomes a problem as the cold front 
pushes through the area and is further complicated due to differences 
in models. Have trended toward the slower NAM/ECMWF/CMC solutions which place 
the cold front just outside the County Warning Area at 12z Sat. Experimental rain to change over to 
pl as cold air is advected in at the surface. A brief period of freezing rain may be 
possible...but have the dominant experimental p-type in the forecast for now. 


Have trended temperatures toward warmer MOS for Friday and Friday night to account for 
slower frontal passage...then cooler on Sat as strong surface ridge moves into the 
area. Have made little or no changes to previous forecast beyond Sat. 




Tilly 


&& 


Aviation... 
/1120 am CST Wednesday Jan 7 2009/ 
for the 18z tafs... 
first area of low clouds over Illinois/eastern MO with ceilings ovc024-032 will 
move out of the taf sites 18-20z...but then ovc025 ceilings will move 
back into KUIN from Iowa around 21z. Farther south...ceilings ovc080 
will move in 19-21z followed by ceilings ovc025 in the early evening 
00-02z. Prob30/tempo 4sm -sn ovc015 groups at kcou/kstl/ksus this 
evening still look good...but have moved the timing up by a couple 
of hours. Some minor snow accumulation will be possible early this 
evening in the band of snow...1/4 inch or less. Then low clouds 
should clear out 04-07z leaving scattered middle-high clouds. 


Britt 


&& 


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


$$ 


Weather forecast office lsx