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fxus63 kilx 191915 
afdilx 


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


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 
&& 


Aviation... 
issued 652 am CDT Friday Mar 19 2010 


VFR conditions will continue next 24hrs at all taf sites. Just 
some high cirrus ahead of the cold front that is expected to move 
through all sites today or this evening. Front will move south and 
should move through pia first around 22z. Bmi will be next around 
00z followed by spi...Dec and cmi at 01...02 and 03z respectively. 
Precipitation will start in pia late while other sites will not see precipitation 
until after 12z. Southwest winds ahead of the front with wind 
transitioning to northwest...then north-northeast. Winds will also 
increase in speed. 


Auten 
&& 


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


$$