Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 122348

Area Forecast Discussion
National Weather Service Lincoln IL
548 PM CST Tue Dec 12 2017

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 258 PM CST Tue Dec 12 2017

A surface high pressure ridge and associated light winds will cross
over central IL this evening. After this, the clipper system
currently over Alberta heading toward northeastern IL will approach,
increasing southerly winds for early in the morning. Temperatures
will drop into the low 20s early in the night, steadying through
early morning with the increase in southerly winds. By noon
Wednesday, the cold front associated with this fast moving system
should already be approaching the Illinois River, with temperatures
peaking for the day early just before frontal passage, and winds
shifting to NW behind the front. Expect highs ranging from around 40
on I-74 to mid to upper 40s from Jacksonville to Lawrenceville.
Boundary layer momentum looks to be quite strong, with 925 mb winds
up to 35 kts. Have therefore raised wind speeds for the Wednesday
forecast, with sustained wind speeds reaching 20-25 mph and some
gusts reaching 40 mph. Also included a chance of precipitation
mainly along and north of I-74, and a slight chance extending
southward to Havana, Lincoln, and Paris. Precipitation should be a
mix of rain and some snow from I-74 northward. Amounts of
precipitation should be only a few hundredths or less, with no
expected snow accumulation.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 258 PM CST Tue Dec 12 2017

The next system looks on track for Thursday night into Friday
morning, although models show little indication of precipitation
this far south. Highs expected in the low to mid 30s Thursday and
Friday, and lows in the low to mid 20s Thursday morning through
Saturday morning.

Starting Saturday, a warmup looks on track as the longwave ridge
over the west moves eastward and milder pacific air advects into the
central and southeast U.S. ahead of a trough moving digging into the
mountain west. Highs well into the 40s can be expected over the
weekend into early next week as a result. Uncertainty develops in
how the trough evolves into next week, however fairly good agreement
that a disturbance embedded in southwesterly flow will bring some
precipitation to areas south of I-70 Sunday or Monday.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 548 PM CST Tue Dec 12 2017

A brief break from gusty winds is expected this evening. However,
another low approaching from the NW will bring increasing S-SW
surface winds and winds aloft by late tonight into early Wednesday
morning. As a result of strong SW winds aloft, have included low
level wind shear from 10-15Z at all TAF sites due to 45 kt flow
at 1500 ft AGL. CMI and DEC will be the latest to see LLWS, but a
few hours from 12z-15z or so could see those conditions as well.
As a cold front approaches and then passes tomorrow, winds will be
shifting from S-SW winds to start the day, then become westerly in
the afternoon while continuing at 15G30kt. Winds will eventually
become NW by late in the TAF period, once FROPA occurs.

Cloud heights look to approach MVFR by mid to late afternoon
tomorrow, with the TAF sites along the I-74 corridor having the
better chances of dropping down into MVFR levels. No precip of
significance is expected, although a few sprinkles could develop
with the frontal passage.




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