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fxus63 kilx 200830 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
330 am CDT Sat Mar 20 2010 


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 


&& 


Aviation... 
issued 1200 am CDT Sat Mar 20 2010 


Surface boundary has progressed slowly to a line ikk-aaa-ppq. Vertical slope 
of the frontal zn is quite gradual...with stronger winds/lower clouds and 
precipitation lagging the lead wndshft by more than 50 Michigan. Precipitation is currently 
aligned along zn of low/middle level frontogenetic forcing from irk-rfd...and 
this zn is moving only slowly southward. Expct precipitation to come into pia as rain 
toward dawn...then become a mixture rasn as deeper cold air comes S. Forecast 
models suggest that insufficient cold air will come further S into the 
other cntl Illinois taf sites to produce a meaningful threat of snow...so 
have removed mention of mixture at bmi. Morng precipitation will likely weaken and 
become more scattered toward midday as baroclinic zn weakens and emphasis shifts 
southwestward to rapidly deepening upper low and its associated surface cyclogenesis over 
Arkansas. So after 00z sun...will only mention a tempo for -ra for the 
spi-Dec-cmi corridor and keep pia/bmi dry for now. 


04 
&& 


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


$$