722 
fxus63 kilx 091126 
afdilx 


Area forecast discussion 
National Weather Service Lincoln Illinois 
526 am CST Friday Jan 9 2009 


Discussion... 
issued 227 am CST Friday Jan 9 2009 


Main short-term concern will be chance for accumulating snow 
across parts of central Illinois late tonight into Saturday 
morning. After that...big story will be the bitterly cold conditions 
expected by the middle and end of next week. 


Latest surface chart shows low pressure organizing over the 
Dakotas...with warm front stretching east/southeast across southwest Iowa 
into central Missouri. Band of clouds and light snow has developed 
north of this boundary...primarily across Iowa. Aloft...northwest 
flow pattern is noted across much of the Continental U.S.. one weak short-wave 
embedded within the flow is helping trigger the light snow across 
Iowa...while a stronger wave is poised further upstream across the 
northern rockies. 


Short term...today through Sunday 


Warm front will lift slowly northward today...with best 
frontogenesis and forcing shifting northward as well. May see a 
few snow flurries across the far north/northwest kilx County Warning Area early this 
morning...but do not think chance is great enough to mention in 
the forecast. Primary band of snow will set up across northern 
Iowa east/southeast across northern Illinois today. Further south across 
central Illinois...surface flow will veer to southerly as the day 
GOES on...bringing warmer air northward into the region. With 
front expected to remain near the I-80 corridor...winds across the 
northern County Warning Area will maintain an easterly component throughout the 
day. As a result...temperatures along and north of the I-74 corridor will 
stay a bit cooler...with highs only reaching the middle to upper 
30s. Elsewhere...readings will climb into the lower to middle 40s. 


Northern rockies short-wave will push into the region tonight...with 
associated surface low pressure tracking from northern Missouri 
across south-central Illinois. With this particular storm 
track...heaviest precipitation will likely occur along and north of the 
I-74 corridor. Thermal profiles will initially be warm enough to 
support all rain during the evening...except perhaps a rain/snow mix 
from Peoria northward. With best lift still off to the N/NW...will 
only carry chance probability of precipitation before midnight. Overnight...low will push 
further eastward and much more favorable lift/dynamics/moisture 
will exist across the area. Will therefore bump probability of precipitation into the 
likely category across the board after midnight. Based on 
NAM-WRF/GFS forecast soundings...it appears the primary precipitation 
type later tonight will be snow along and north of I-72...with a 
rain/snow mix further south to I-70...then all rain south of 
there. 


As low moves into Indiana early Saturday morning...precipitation will 
linger across central Illinois...particularly across the east. 
Will therefore carry likely probability of precipitation along and east of I-57...tapering 
down to low chance probability of precipitation across the Illinois River valley. Precipitation 
will come to an end by afternoon...with only a few lingering 
flurries expected. With tightening pressure gradient 
developing...expect windy and colder conditions. West/northwest winds of 
between 10 and 20 miles per hour will be common...with gusts up to 30 miles per hour at 
times. Total snow accumulation from this storm system will 
generally be around one inch along and northeast of a Springfield 
to Mattoon line...with perhaps one to two inches along and 
northeast of I-74. 


The next in a series of northwest flow clipper systems will swing 
through the upper Midwest on Sunday. 00z Jan 9 models continue to 
suggest this feature will remain north of central Illinois...so 
will maintain dry forecast at this time. Will however increase 
cloud cover...particularly across the north. 


Long term...Monday through Thursday 


Yet another clipper system is prognosticated to track into the area early 
next week...bringing a period of light snow Monday and Monday 
night. Based on good agreement on the timing of this feature 
between both the GFS and European model (ecmwf)...have raised probability of precipitation to 40 on Monday. 
First installment of Arctic air spills into the Midwest behind 
this wave for Tuesday and Wednesday...with high temperatures both days expected 
to struggle into the teens. A stronger push of bitterly cold air 
will arrive Wednesday night into Thursday...with high temperatures by the 
end of the week remaining in the single digits and overnight lows 
dropping below zero. Exact magnitude of cold will depend upon 
extent of snow cover next week. Have trended temperatures downward...but 
these readings may need to be lowered further if trends continue. 






&& 


Aviation... 
issued 520 am CST Friday Jan 9 2009 


VFR conditions are expected through 23z across the forecast area. Warm 
advection band of clouds and snow have pushed across the far northern 
portion of the forecast area over the past several hours with the 
back edge of the snow now to our east. Band of middle and high level 
moisture to follow for today with scattered-broken ac deck across most of the 
area. Main storm system to push across the forecast area this 
evening with the surface low shifting to our south...resulting in surface 
winds backing into the east and then north late tonight into Sat morning. 
Light precipitation expected across the area later this evening as the system 
approaches with forecast soundings suggesting a brief period of light 
rain followed quickly by a changeover to light snow. There may be 
a brief period of light freezing rain or sleet but soundings indicate 
in most areas just an hour of freezing precipitation before going over to 
light snow. With the precipitation developing this evening...look for MVFR 
ceilings and visibilities to drop to IFR to possibly LIFR ceilings and visibilities in light 
snow north...and a mix of snow and rain initially at spi and Dec 
quickly going over the light snow. Southeast winds today will back into 
the east overnight and then north on Saturday. May see some gusts 
for a few hours this morning...with northeast to north winds gusting to 
between 20 and 25 kts by Sat morning as the storm system pulls away from 
central Illinois. 


Smith 
&& 


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


$$ 

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