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fxus63 klsx 201158 
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Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
658 am CDT Sat Mar 20 2010 


Discussion... 
/446 am CDT Sat Mar 20 2010/ 


Banded precipitation currently moving through western MO...and extends into southeastern 
Iowa and northwestern MO. This is associated with strong frontogenetical 
lift behind a Stout cold front that is now near a khuf-kuno line...and 
is through stl metropolitan. Temperatures rapidly fall off into the 30s behind this 
front but do not actually attain this for nearly 75nm behind the 
front. 


Of most concern is this banded precipitation...of which the higher 
reflectivities have already dropped 3-4 inches of snow in short 
order in northwestern MO. This favorable area will slide eastward into the western 
edge of the forecast area today...including northestern and central MO...and then 
gradually fade late tonight and Sunday morning. Vertical temperature 
profiles will be critical...and it appears that these will be most 
favorable for snow today before the Southern Plains system gets wrapped 
up and begins to push back the cold air to the west with its warmer 
air aloft. This will ultimately change the snow with some sleet 
over to rain with some sleet later tonight and this will continue 
into Sunday morning. Therefore...much of the expected snow accumulate 
will occur today over the advisory area...which has been expanded 
to include more of central MO...where 2-5 inches are anticipated. 
Would not be surprised to see a few spots approach 6 inches if 
bands are persistent enough. Farther to the S and east...including 
stl metropolitan...look for just rain out of this system...with most of 
it occurring later tonight and Sunday. 


By the time the system gets going enough to push its deformation 
zone precipitation into the forecast area by Sunday...and continue through Sunday night 
and into Monday morning...precipitation should be all rain except for some 
sleet and snow possible in northestern/central MO. 


A large temperature gradient will setup across the forecast area today as a result 
of the slowing down cold front with temperatures in the 50s pushing 60f in the 
far southeastern forecast area and remaining steady in the 30s in the northwestern forecast area from 
KUIN to kcou. This will be short-lived...as by Monday...even the 
areas that receive snow today will be rebounding into the 50s. 


Tes 


&& 


Aviation... 
/641 am CDT Sat Mar 20 2010/ 


Complex weather setup for the next 24 to 36 hours for cou/uin. 
Precipitation should begin soon at uin...initially as rapl before changing 
quickly to snow. Light rain has already started at cou and is expected 
to change to snow soon too. Precipitation should be mainly snow this morning. 
However...precipitation type becomes complicated this afternoon and 
evening as warm air is advected in aloft. This will provide for a 
mix with all types being possible. Late tonight into Sun morning 
precipitation should switch over to all rain. There is uncertainty regarding 
when precipitation will end...but precipitation should continue into Sun morning. 
Expecting 2 to 4 inches of snow accumulation for cou and uin by 12z 
Sunday. For sus...please see discussion below for stl. 


Specifics for kstl...believe cloud deck with ceilings around 1500 feet 
will move in very soon to terminal. Terminal will be on the eastern edge 
of the precipitation shield this afternoon and believe any precipitation will 
hold off until the evening hours. Precipitation will be all rain this evening and 
overnight. Some uncertainty exists as to when precipitation will end. 
Believe precipitation will end early Sun morning before beginning again 
Sun afternoon. 


Tilly 


&& 


Lsx watches/warnings/advisories... 
MO...Winter Weather Advisory until 1 PM CDT Sunday for Audrain MO- 
Boone MO-Callaway MO-Cole MO-Knox MO-Lewis MO-Marion MO- 
Moniteau MO-Monroe MO-Ralls MO-Shelby MO. 


Illinois...Winter Weather Advisory until 1 PM CDT Sunday for Adams Illinois. 


&& 


$$ 


Weather forecast office lsx