Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 221120

Area Forecast Discussion
520 AM CST Mon Dec 22 2014

.SHORT TERM...(Today)

Strong jet (175kts) over the Pacific Northwest digging southeast
into a deepening central Plains trof this morning will eject an
initial wave into our area today bringing rain along with mild
temperatures. Low pressure is expected to consolidate over north
central Missouri by late this afternoon and then track thru
northwest Illinois early this evening. The southerly flow in advance
of the storm system will quickly saturate the lower levels of the
atmosphere with rain overspreading the area from southwest to
northeast this morning. Some weak isentropic lift and moisture
convergence early this morning has produced some spotty light
rain/drizzle over parts of central Illinois and expect that to
continue before the stronger forcing arrives later this morning.
Models suggest the strongest lift moves into our area from mid
morning thru the early evening hours, so high POPs are warranted
over most of the forecast area today. Despite the cloud cover and
precip, mild temperatures to prevail again today with afternoon
readings in the mid to upper 40s.


.LONG TERM...(Tonight through Sunday)

Increased rain chances to categorical this evening with supporting
lift of low level jet and short waves ejecting ne from
central/southern plains into IL tonight. Rain chances to diminish
from sw to ne during overnight into Tue morning as energy shifts
north of central IL Tue. Appears to be a lull in rain chances Tue
and Tue evening over much of central IL with best rain chances
shifting to our north with surface low pressure over southern WI Tue
afternoon and also to our se. Mild lows tonight of 40-45F and highs
Tue range from mid 40s over IL river valley and lower 50s in
southeast IL.

00Z models still not in good agreement with development of strong
low pressure system from northwestern Gulf of Mexico and deepening
nne across the ohio river valley Wed. NAM model appears is dry over
IL Tue night and Wed but feel its low pressure track is too far east
near the foothills of the Appalachians. Will use a blend of the
ECMWF/GEM and GFS models for the storm system during midweek. Have
precipitation chances spreading back northward across central IL
overnight Tue night into Wed and diminishing from west to east by
overnight Wed night. Warm enough for rain Tue evening, then mixing
with and gradually changing to light snow later Tue night into Wed
from west to east. Deformation band of light snow accumulations
likely to set up on back side of storm system, though placement of
this band is still too difficult to pinpoint down. WPC keeps snow
accumulations less than 1 inch over central/eastern IL on
Wed/Christmas eve. Cooler highs Wed in the upper 30s to near 40F
eastern IL and will likely slip during the afternoon with increasing
WNW winds.

Christmas Day still looks dry with return of some sunshine as strong
storm system lifts into Quebec and 1025 mb surface high pressure
over gulf of mexico ridges northward into the ohio river valley.
Highs in the lower 40s Thu/Christmas Day, so any snow that does fall
Wed will likely melt.

Models have another low pressure taking a track more nw of central
IL Friday and lifting into the western Great Lakes Friday night.
Have small chances of light precipitation Fri/Fri night and then dry
for the weekend. Models showing yet another southern low pressure
system over gulf of Mexico Sat night/Sunday but for now will keep
precipitation chances south of central IL.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)

Deteriorating conditions expected across the area this morning
as a storm system tracks into the region. Mostly VFR cigs being
reported early this morning but expect those to transition to
MVFR and then IFR from south to north after 15z this morning as
rain increases in coverage over our area. We expect IFR to LIFR
conditions this afternoon into tonight as the rain continues on
and off thru 00z. In the 03z-06z, the rain is expected to taper
off with a lull in the precip after 06z as the storm system shifts
north of our area overnight. Surface winds will be east to southeast
today at 10 to 15 kts with a few gusts around 20 kts later this
morning into the afternoon hours. Southeast winds of 10 to 15 kts
can be expected tonight.




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