Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 202000

Area Forecast Discussion
National Weather Service Lincoln IL
300 PM CDT Tue Mar 20 2018

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 300 PM CDT Tue Mar 20 2018

Chilly conditions for the first day of Spring will continue in the
near term as persistent upper troughing/northwest flow remains
over the Midwest. An upper low in western KY, along with weak
shortwave troughs dropping into the mean upper trough position,
will result in periods of light rain, mixed at times with snow in
extreme east central and southeast IL this eve through tonight.
KILX radar already shows where the bands of mid level clouds are
setting up...generally east of I-57...and on the far northwest
edge of the large precipitation shield that is expected mainly
toward IN and KY.

Otherwise, clouds and a brisk northerly wind will dominate in the
rest of central Illinois through tonight and into Wed morning. As
the upper low quickly shifts toward the central Appalachians by
daybreak, drier air will move into the area resulting in
decreasing clouds and continued cool temperatures in the mid 40s
across most of the area.


.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 300 PM CDT Tue Mar 20 2018

A rather active weather pattern will be in store for central and
southeast IL from later Thursday through the early weekend and
again early next week...with periods of rain and even some
accumulating snow possible.

Increasing mid level warm advection during the day Thursday will
set the stage for the next round of precipitation from west
central IL to parts of central and SE IL from Thursday afternoon
into early Friday morning. Most of this should be in the form of
rain, although a little snow may mix with the rain in SE IL before
ending Fri AM.

The biggest challenge will be the timing and precipitation types
for later Friday through Saturday with a low tracking from the
central Plains toward southern IL. Due to the presence of a dry
easterly flow on Friday there is low confidence that rain will
spread too far east during the day, so will go with low chance
PoPs for now. The atmosphere is expected to eventually moisten by
Friday night, but this will also result in evaporational cooling
through the column resulting in a question of precipitation type
for central IL. For now it appears that locations north of a
Galesburg- Clinton-Paris may cool enough for all snow from late
Friday night into Saturday morning...but this bears watching since
it is still 4 days out in the forecast. This scenario would be
capable of producing 1-2 inches of wet snow mainly along and north
of I-74 by mid-morning Saturday.

From Saturday through Tuesday the models diverge fairly
significantly. On Saturday the GFS is quicker with the
aforementioned low, while the Euro and Canadian are about 6 hours
slower with the low track. For now the slower solution of keeping
rain in the forecast for Saturday appears better as upper ridging
building from the Upper Great Lakes into western Quebec should
slow the progression of things a bit. After a lull on Sunday with
nearly seasonable temperatures, the return to precipitation for
early next week appears likely. However, the timing is highly
uncertain, with the GFS once again being the quicker model. The
most prudent thing to do at this point is to stick with a blended
solution of low PoPs for Monday, with increasing chances for rain
later Monday into Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1223 PM CDT Tue Mar 20 2018

VFR conditions will prevail through the TAF period the next 24
hours in central Illinois. The main concern for this afternoon and
early this evening will be gusty north to north-northeast winds
caused by a strengthening low pressure center moving up the west
side of the Appalachians toward the upper Ohio River valley.

This low pressure area, combined with shortwave energy from the
upper Midwest dropping into the mean upper trough axis, will keep
clouds over the forecast area through tonight and into Wednesday
morning. The best upper forcing is expected to be well to the
southeast and east, so the clouds will remain in the VFR category.
As the low rapidly shifts eastward, a clearing trend is expected
by mid-morning Wednesday, along with lighter wind speeds.




LONG TERM...Miller
AVIATION...Miller is the U.S. government's official web portal to all federal, state and local government web resources and services.