844 
fxus63 kilx 201750 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
1250 PM CDT Sat Mar 20 2010 


Discussion... 
issued 1038 am CDT Sat Mar 20 2010 


Latest surface analysis shows strong cold front stretching from 
Indianapolis southwestward to near Mount Vernon Illinois. Ahead of 
the front...southerly winds continue to bring warm air into the 
far southeast kilx County Warning Area...with current temperatures south of I-70 in the upper 
50s. North of the boundary...stiff northeasterly winds have 
brought sharply colder conditions to the rest of central Illinois. 


A persistent band of precipitation associated with the 850mb front 
continues to flow northeastward across the Illinois River valley. 
With the upper-level front expected to remain nearly stationary 
throughout the day...precipitation area will likely not shift much 
further eastward. RUC model seems to be handling current situation 
the best...and it keeps the bulk of the precipitation across the western 
half of the County Warning Area through the afternoon. Based on RUC data and radar 
mosaic...have dropped all mention of precipitation across east-central 
and southeast Illinois. Further west...will go with categorical 
probability of precipitation along and west of I-55. 


Precipitation type has been a mixture of rain...sleet...and snow along 
and just west of the Illinois River...with mainly snow further 
west across Knox and Stark counties. As profile cools by a few 
degrees...mixed precipitation will shift east of the river this 
afternoon...with snow continuing further west. 1 to 2 inches of 
snow will accumulate along and west of the Illinois River...while 
only rain showers will impact the I-55 corridor. Zone update has 
been sent to better reflect current trends. 






&& 


Aviation... 
issued 1250 PM CDT Sat Mar 20 2010 


Band of precipitation currently over the Illinois River valley will 
remain in place for the balance of the afternoon into the evening 
hours. Meanwhile...an upper-level wave tracking northeastward out 
of Missouri will help spread showers as far east as the I-55 
corridor. Based on radar timing tools...will introduce light rain 
at kspi between 18z and 22z and further north at kbmi between 19z 
and 23z. Further east...dry conditions will likely continue at 
the eastern terminals...so have only included a vcsh at both kdec 
and kcmi. Meanwhile...light snow with ceilings around 1000ft will 
persist at kpia. As warmer air is advected in aloft tonight...the 
snow will gradually mix with and change to rain at kpia. Once the 
upper wave lifts out of the area...models are indicating a gradual 
end to to the precipitation after midnight. Winds through the entire 18z 
taf period will remain gusty out of the northeast. 


Barnes 
&& 


Previous discussion... 
issued 330 am CDT Sat Mar 20 2010 


Forecast concern is how much snow will fall across the Illinois River 
valley through tonight...and still looks like 1-3 inches northwest of the 
Illinois River today into tonight. 00z short range models trending slower 
with frontogenetic precipitation moving slowly southeast into central Illinois 
this morning. Light snow is still northwest of Galesburg and Quincy at 3 
am. NCEP feels NAM and GFS maybe a bit too far south with weather 
systems this weekend and trended quantitative precipitation forecast fields a bit further north 
than these two models protrayed. Strong upper level low that moves 
east across the southern states has increased rain chances Sunday 
afternoon/night east of I-55. 


Early morning surface map shows a cold front moving slowly southeast 
across central in/Illinois toward I-70 and into southeast MO to 1011 mb low 
pressure in northwest Arkansas and stronger 1007 mb low pressure in SW Texas. Post 
frontal precipitation in from of light to moderate snow has been 
from Rockford to quadrant cities to Kirksville and still northwest of 
Galesburg and Quincy. Temperatures have fallen to the middle to upper 30s northwest 
of the Illinois River with north winds 10-20 miles per hour and gusting to 20-30 miles per hour. 
While 40s southeast of the Illinois River. 


Short term...today through Monday night. 


Models slow down cold front as it moves into southeast Illinois today while 
frontegenetic forcing and isentropic lift behind the cold front 
brings rain/snow southeast across the Illinois River valley this morning and 
into central Illinois this afternoon in form of rain from I-55 east. 
Mixed precipitation turns to snow by afternoon across the Illinois River 
valley. Just a slight chance of rain showers southeast of I-70 this 
afternoon near the frontal boundary. About a 30 degree temperature 
spread today for highs across County Warning Area ranging from 36f far northwest by 
Galesburg to 65f far southeast Illinois by Lawrenceville where ahead of cold 
front and some peaks of sunshine especially this morning. 


Lowered precipitation chances tonight as frontogenetic forcing 
weaks over central Illinois while forcing focused SW of Illinois closer to 
strong upper level low developing over the Southern Plains. Still 
have likely chances of light snow over the Illinois River valley this 
evening then turns back to a mix of rain overnight as warmer air 
at 850 mb moves northwest. Areas northwest of the Illinois River could see 1-3 inches 
with hihgest amounts from Galesburg to Macomb to Rushville west. 
Below Snow Advisory criteria of 3 inches. 


Rain chances increase by Sunday afternoon across areas east of 
I-55 and especially Sunday night as strong upper level low moves 
into the southern Tennessee Valley. Storm Prediction Center has chances of thunder just southeast of 
Lawrenceville Sunday night so this will need to be watched for if 
southeast Illinois needs thunder mentioned. Increase quantitative precipitation forecast amounts across southeast Illinois 
Sunday afternoon and Sunday night and this may cause some rivers 
to go back into flood. Followed cooler guidance highs Sunday with 
low clouds and rain chances increasing especially eastern/southeast Illinois. 


Chances of light rain Monday over eastern Illinois east of I-55 mainly Monday 
morning as upper level low exits east of the Tennessee Valley. 


Long term...Tuesday through Friday. 


Dry weather expected from Monday night through Wednesday with temperatures 
modifying as upper level ridge briefly builds back into Illinois. 
Removed slight chance of rain Wednesday as extended models in agreement 
of next weather system being slower to eject NE from the Southern 
Plains toward the Midwest. Next best chance of rain will be 
Thu/Fri. 


Huettl 




&& 


Ilx watches/warnings/advisories... 
none. 
&& 


$$ 

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