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Area forecast discussion 
National Weather Service Lincoln Illinois 
835 PM CDT Friday Mar 19 2010 


Discussion... 
issued 835 PM CDT Friday Mar 19 2010 


Cold front moving through Illinois has reached Peoria and will 
continue overspreading the remainder of the area overnight. 
Precipitation is well northwest of the frontal boundary...and will 
hold off for a couple more hours for our forecast area. Expect light 
rain to enter the Galesburg area around 10pm or shortly thereafter 
and progress southeastward to around Interstate 55 by dawn. Still 
expect mainly rain...but forecast soundings from the 00z RUC hi-res 
model for Galesburg suggest a mixture or change-over to snow toward 
12z Sat. Same sounding forecasts centered over Peoria indicate all 
rain. Therefore the current forecast looks on target and do not plan 
on any changes at this time. May make some hourly grid adjustments 
here and there...but thats about it. 


04 
&& 


Aviation... 
issued 615 PM CDT Friday Mar 19 2010 


Cold fnt to the northwest is moving very slowly southeastward...having only just passed 
gbg. Boundary forecast to arrive pia 02z...bmi 04z...and spi/Dec/cmi 
06z-08z Sat. Scattered-broken 4k-5k feet stratocu will be the rule for a few hours 
after frontal passage...with precipitation coming into pia about 09z Sat. Precipitation type at pia 
will be rain to start off followed by a rasn mix by 14z Sat then all 
-sn after 18z. Precipitation should be all liquid at bmi until -sn begins to mix 
in after 20z. The depth of cold air should be insufficient for 
anything but rain for spi/Dec/cmi...where coverage will be a bit more 
spotty Sat afternoon. Expct ceilings/visibilities in the VFR range until the onset 
of precipitation...with 3-5sm visibilities and 1500-2500 feet ceilings thereafter. 


04 
&& 


Previous discussion... 
issued 200 PM CDT Friday Mar 19 2010 


Cold front making slow progress southeast into northwest Illinois early this 
afternoon. Front still northwest of Galesburg with temperatures 
ahead of the boundary ranging from the middle 60s to around 70 over our 
far southeast counties...while behind the front...early afternoon temperatures 
across central and western Iowa were in the middle 30s with light snow. 
Overall... not too many differences seen with the short range models 
with respect to the frontal movement across the region over the next 
24 hours and timing of precipitation into the forecast area late tonight into 
Saturday...with our east and southeast counties last to see the rain 
move in later on Saturday. Temperatures some 25 to 30 degrees colder 
over our northern and centrl counties on Saturday! 


Main forecast challenge will be precipitation type and amounts late tonight and 
Saturday...especially west of the Illinois River...along with temperatures this 
weekend. 


Short term...tonight through Monday night 
cold front to push slowly across the forecast area tonight with the 
combination of isent lift and some fairly decent frontogenetical 
forcing leading to an eastward shift in the snow and rain into our 
far west and northwest counties aftr midnight...with a changeover to 
snow by dawn. Forecast soundings suggest the potential for a brief 
period of sleet as well but based on the sounding data...not long 
enough to mention in the grids at this point across the northwest. 
Looks like mostly snow by dawn across the far northwest with a 
rain-snow mixture further southeast along the Illinois River valley. 
Precipitation going to have a tough time making much progress east of 
Interstate 55 until the afternoon with soundings much slower in saturating 
the lower levels. The main band of forcing/lift moves across the 
forecast area during the daylight hours on Saturday with temperatures in 
the area of greatest lift/steadier precipitation still forecast to be in 
the middle 30s...and coupled with the fact we have been in the 60s the 
past svl days (and 2 inch soil temperatures well into the 40s)...not a real 
good setup for sig snow accumulations. Still looking at 1 to 3 
inches west of the Illinois River Saturday...and an inch or less 
east of the river. Based on the reasoning above...will hold off any 
headlines across our far northwest for Saturday. 


Zone of lift/frontogenetical forcing remains basically in the same 
area through the day Saturday...roughly west of a Springfield to 
Bloomington line with a gradual weakening trend noted towards evening 
as the main forcing sets up further southwest...closer to the 500 mb 
closed low across TX/OK. Forecast soundings continue to show warmer 
temperatures shifting back west/northwest across the area later Saturday evening 
into Sunday as the upper wave across the Southern Plains and surface low 
shift east. Soundings still support a snow rain mixture west of the 
Illinois River...with rain to the east. As the surface low shifts into western Kentucky 
late Sunday...models indicate another area of lift to the northwest of the 
surface low track affecting mainly our central and southeast counties 
with a steady cold rain late sun into Monday. 


Models continue with a slower and further south trend with respect 
to the closed upper level system across the Southern Plains this weekend. 
Although the NAM-WRF was furthest north...it too has trended further 
south over the past svl runs. Except for our east and southeast 
counties where the precipitation may hold off for a time Saturday to allow 
temperatures to warm ... conditions over the remainder of the area 
similar to last weekend with damp and chilly conditions coupled with 
a raw NE wind. 


Long term...Tuesday through Friday 
the weather expected to quiet down some by Tuesday as upper level and 
surface ridging builds into the Midwest. Very active southern stream 
forecast by medium range models to continue through most of next week 
bringing in a series of shortwaves which will dive into the Southern 
Plains and eject NE in the Midwest. Ensembles still showing quite a 
bit of spread with respect to timing and strength of the first wave 
late Wednesday or Thursday of next week. As a result will not make any 
changes to our current low chance probability of precipitation for later Wednesday into Thursday. Temperatures 
will certainly rebound once we lose the NE winds and clouds on Tuesday 
and Wednesday of next week...with readings back into the upper 50s to 
lower 60s through mid-week...with a trend towards cooler weather behind 
the midweek shortwave late in the work week. 


Smith 
&& 


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


$$