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fxus63 klsx 220438 
afdlsx 


Area forecast discussion...updated aviation 
National Weather Service St Louis MO 
1138 PM CDT sun Mar 21 2010 


Discussion... 
/235 PM CDT sun Mar 21 2010/ 


Main challenge initially deals with when precipitation will exit the 
area. There is good agreement amongst the models that the upper low 
currently along the Arkansas/la border will lift northeastward into eastern Tennessee 
by late Monday. This will cause the deformation zone rain that 
currently covers the southeastern half of the County Warning Area to slowly end from west to 
east over the next 24 hours. Will have a sharp pop gradient on the 
northern edge of the deformation and will keep categorical probability of precipitation this 
evening basically where it is raining now with dry probability of precipitation going from 
cou northeastward into uin...and then shift it slightly eastward overnight. Kept 
chance probability of precipitation going over southwestern and S central Illinois on Monday morning before 
ending it by afternoon. Forecast soundings are showing the low level 
thermal profiles will remain above freezing until the precipitation 
ends. Area will lie under large scale subsidence as ridging builds 
in behind the upper low...so have dry weather going through 
Wednesday. 


Went toward the cooler NAM MOS for highs tomorrow which is supported 
by mixing down 925mb temperatures from both the NAM/GFS. Central MO may be 
inhibited a bit by western MO snow pack and clouds will take a while 
to clear in the east. Mostly sunny skies and southwesterly winds ahead of a 
cold front justify the warmer GFS MOS temperatures on Tuesday. 


Two storm systems will bring precipitation to the area on 
Wednesday night into Thursday night...and then again Saturday 
night and next Sunday. While there is some continuity issues 
within the individual medium range models...they are showing 
decent agreement with the timing of both systems. Soundings and 
forecast surface temperatures still suggest there will be no 
freezing/frozen precipitation with these late March systems and do not 
see enough instability or low level moisture to include thunder at 
this time. 


Britt/Byrd 


&& 


Aviation... 
/1109 PM CDT sun Mar 21 2010/ 


Low pressure system to the southeast continues to spread -ra across 
parts of MO and Illinois. Radar echoes have begun to decrease in 
coverage and intensity over the County Warning Area and this trend is expected to 
continue overnight with -ra gradually diminishing from northwest to southeast by 
daybreak as the system moves away from the region. Cloudiness should 
decrease during the day at KUIN/kcou with VFR conditions expected 
by afternoon as a ridge of high pressure builds in at the surface. Beyond 
the end of the taf period...bufr soundings suggest potential for fog 
after 23/06z however dry conditions seen in upstream observation may 
inhibit fog formation. 


Specifics for kstl...ceilings at kstl have remained steady at 1000 feet 
over the past several hours however a brief dip into IFR range is 
still possible. Rain will persist for the next few hours before 
tapering off near daybreak. Ceilings will rise during the day with 
VFR conditions expected by late afternoon as a ridge of high pressure 
builds in behind the departing system. 


Kanofsky 


&& 


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


$$ 


Weather forecast office lsx