Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291135

Area Forecast Discussion
635 AM CDT Mon Sep 29 2014

.SHORT TERM...(Today)

Weak high pressure will provide another sunny and mild day across
central IL. Some early morning ground fog will develop in low lying
areas mainly near rivers and streams, but it will dissipate quickly
after sunrise. Some diurnally driven cumulus clouds in the 5-7k ft
layer could develop again today, based on the moisture profiles in
forecast soundings. Still plenty of dry air above and below that
moisture layer will mix together to keep clouds in check. Winds will
become north to northwest at 4 to 7 mph today, as a winds flow
clockwise around high pressure centered over N Missouri.


.LONG TERM...(Tonight through Sunday)

Shortwave evident on water vapor imagery across northern parts of
North Dakota and Minnesota early this morning, and this should pinch
off into a closed low over lower Michigan by late evening. Latest
model guidance is pushing the associated surface boundary a bit
further south than previous runs, perhaps as far as I-72 by Tuesday
morning. However, the main energy will be near the closed low, so a
dry passage is on tap for us. Highs on Tuesday behind the front
should be in the mid to upper 70s across the northern CWA, with the
cooler 60s in northern Illinois. Some bust potential for highs
across the south if the front makes more progress than expected, but
will keep 80-85 degrees going there.

Main focus remains with midweek storm system. Upper low currently
spinning across southern Nevada, and is still progged to lift into
North Dakota by late Tuesday evening. As this feature lifts into
Canada, a deep long wave trough will drop across the Rockies on
Wednesday, reaching the Mississippi Valley by early Friday. The
trailing cold front from the earlier system should be moving into
the state on Thursday, with its speed depending on a surface low
riding along the boundary as the upper trough approaches. Severe
weather parameters are fair, with MUCAPE values of 500-1000 J/kg and
0-6km shear around 40 knots across the southern half of the CWA, per
the GFS and ECMWF models, as dew points rise into the upper 60s.
Initial surge of showers and storms expected to move in from west to
east Wednesday night, with likely PoP`s everywhere by Thursday. Some
model spread by Thursday night as to how fast the precipitation
ends, as the GFS is much slower and lingers the threat most of the
night, while the ECMWF and Canadian models are a bit more
progressive with the upper trough and dry it out west of I-55
already by early evening. Right now, will contain the likely PoP`s
to east of I-55 mainly during the evening.

Decent slug of cooler air to plunge into the Midwest behind this
front, as a cutoff low moves into the Upper Peninsula of Michigan.
ECMWF model brings the zero degree 850 mb isotherm into central
Illinois by late Friday evening, while the GFS is a couple degrees
warmer. Have kept Saturday highs at 60-65 for now, but if these
solutions persist, they would need to be lowered. Latest ECMWF would
give highs in the mid to upper 50s, with the GFS a few degrees

Dry conditions expected during the weekend. Some moderation in
temperatures also on tap as the deeper part of the upper trough
shifts into the northeast states.


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

There is some potential for some patchy MVFR vsbys in fog from
thru 13z for PIA and SPI. Otherwise, VFR conditions are expected
today and this evening. Mid-level moisture evident on forecast
soundings indicate some scattered high based cumulus are expected
after 16z, which should dissipate by 00z. This evening a cold
front will progress south into northern Illinois, with low clouds
trailing close behind. The leading edge of the clouds appear to
start MVFR, but could quickly drop to IFR of 600-800 feet. Current
thinking is that the band of lower clouds will affect our northern
TAF sites (KPIA, KBMI) first between 08z and 09z, and possibly as
far east as CMI toward 11z. Surface winds will become light north
to northwest today under weak high pressure. Behind the front
later tonight, winds will shift to northeast for PIA, BMI and CMI.




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