Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 222058

Area Forecast Discussion
258 PM CST Thu Jan 22 2015

.SHORT TERM...(Tonight)

Area of high pressure extends from northeast Kansas into west
central Illinois early this afternoon. Large stratocumulus shield
remains in place over a large part of the midwest, but is showing
erosion southward from Wisconsin and eastward from the central
Plains. The main forecast concern for this period is the speed of
this erosion. The high will be settling southward across the CWA
this evening, but forecast soundings show a tight inversion around
2000 feet hanging in place. Low level layer humidity plots off the
RAP and NAM suggest the clouds will gradually contract from all
sides. Looking at the forecast soundings off the RAP, the cloud
layer remains about 600-700 feet thick after midnight over most of
the area, but continues to erode from the west and north late in the
night. Have used this contraction philosophy in the sky grids for
tonight, going mostly cloudy everywhere this evening, then becoming
partly cloudy everywhere except east central Illinois after
midnight. With that area keeping the clouds longer, the temperatures
will remain more elevated in eastern Illinois, but went with lows in
the lower 20s across the northwest CWA where the clouds should break
up sooner.


.LONG TERM...(Friday through Thursday)

Mostly quiet weather is expected across central and southeast
Illinois through the next week. However, it can not be said that
completely dry weather is anticipated due to a persistent northwest
upper-level flow that will have mainly weak impulses embedded within
it. Any of these waves have at least the potential for a little
light snow or light rain, depending on the low-level thermal
profiles, but dry conditions are expected more often than not. Also,
most of the weak impulses, not surprisingly, exhibit a spread of
timing and/or track solutions that makes singling out a specific
threat of precipitation difficult at best.

However, there is one clipper system that has been more consistently
agreed upon during the period. This system is still on track to dive
across the Midwest late Saturday night into Sunday night. Not much
of a shift has been seen in the storm track in the latest model
runs, but this system had been trending north lately. At this point,
the ECMWF is the furthest south, crossing northern Illinois on
Sunday. Most other solutions take the clipper across southern
Wisconsin. This track is not terribly favorable for the forecast
area to see much precipitation at all, and what does fall is more
likely to be rain given the more northerly track of the system.
However, thermal profiles on the ECMWF support at least a little
snow across the north before the precipitation threat completely
ends. In any event, barring any southward shift in the storm track,
our local precipitation threat will be pretty minimal.

Temperatures through the next several days will average at or above
normal, with the coolest conditions expected for Monday behind the
late weekend clipper. A better cold shot looks likely beyond this
forecast period, heading into the next weekend.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)

MVFR conditions to prevail at most of the TAF sites through the
evening, with ceilings generally 2000-2500 feet. Have seen some
recent lowering at KBMI below 1000 feet, where visibilities are
still around 3SM at 17Z, but believe this will not last long and
will include a short TEMPO group for IFR ceilings. At KCMI, a
ceilings from about KCMI-KDNV northward along the Indiana border
have mostly risen into VFR range, but there will be some
fluctuations around the 3000 foot height into mid afternoon before
dipping back down again. Winds to be light and variable into much
of the evening, as an area of high pressure settles southward,
before trending more southwesterly late in the night once the high
passes. Have shown general improvements into the VFR range in the
10-13Z time frame.




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