Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 221751
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1151 AM CST Mon Dec 22 2014

.UPDATE...
ISSUED AT 904 AM CST MON DEC 22 2014

Made a quick update to the forecast to increase PoPs to 100
percent as light rain has already spread across much of the KILX
CWA. The exceptions are northwest of the Illinois River and
further east near the Indiana border. Based on radar trends and
latest HRRR and NAM forecasts, light rain will spread across the
remainder of the area over the next couple of hours. May see a
brief period of a rain/sleet mix northeast of I-74 near Rantoul
and Danville as the precip initially begins, but it will quickly
transition to all rain. Also made a few tweaks to hourly temps and
lowered afternoon highs by a couple of degrees due to rain and a
continued E/SE flow.  Highs will reach the lower to middle 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 501 AM CST MON DEC 22 2014

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)
ISSUED AT 501 AM CST MON DEC 22 2014

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 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1151 AM CST MON DEC 22 2014

Upper wave lifting northward from Oklahoma/Texas has spread low
clouds and rain across central Illinois late this morning. Area
surface obs indicate IFR ceilings across the board. Based on 12z
forecast soundings and latest HRRR output, think IFR conditions
will prevail through the afternoon and evening with off and on
rain showers. As the upper system lifts further northward, an
approaching mid-level dry slot will bring an end to the rain from
southwest to northeast across the area after later tonight. HRRR
suggests rain will end at KSPI by 08z, then further northeast to
KCMI by around 11z. Once rain ends, have raised ceilings to MVFR
late tonight into Tuesday morning. Winds will initially be from
the southeast at 10-15kt this afternoon/evening, then will become
southerly tonight. S/SW winds of 10-15kt will prevail by Tuesday
morning.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes






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