Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 281748

Area Forecast Discussion
1248 PM CDT Sun Sep 28 2014


Forecast generally looks on track today and just slight modifications
with sky cover today. A fair amount of sunshine expected again
today with patches of mid/high clouds and few cumulus clouds this
afternoon mainly from I-55 west and over the Wabash river valley.
Warm highs in the low to mid 80s today and Monday with light winds.

Patchy fog along the Wabash and IL rivers dissipated by 830 am
leaving sunny to mostly sunny skies by mid/late morning. 1023 mb
high pressure over lower MI and ridging westward into WI and central
and eastern IA and northern IL will remain over the Great Lakes
through monday and maintain fair wx with warm days. Dewpoints
currently in the mid 50s to near 60F will slip a few degrees this
afternoon so humidity levels will be fairly low again this afternoon.
Temps currently in the low to mid 70s (except 68F at Lacon which
had valley fog earlier this morning) will climb another 10 degrees
into the low to mid 80s by mid afternoon. Weak 580 dm 500 mb low
over far western IA near Nebraska border drift se into MO by
sunset and keep its isolated convection west of IL. RAP/NAM curule
shows few cumulus clouds this afternoon from I-55 west and over
the Wabash river valley in southeast IL. Some patches of mid/high
clouds drift over IL today but still a mostly sunny day expected.


.SHORT TERM...(Today)

A shallow layer of moisture below a subsidence inversion will allow
some patchy ground fog to linger near river valleys early this
morning (IL and Wabash rivers). Any fog should dissipate by 830

The 580dm 500mb low centered over NW Iowa will become an open wave
and drift southeast across IL later today. That will bring scattered
cirrus clouds with it, but sunshine should generally prevail across
IL today. That will help high temps climb above all guidance numbers
again today, as the dry low levels warm quickly. Temps should top
out in the low to mid 80s this afternoon. Winds will remain light
under a weak surface pressure gradient, with east to southeast winds
of 5 to 8 mph again today.


.LONG TERM...(Tonight through Saturday)

Quiet weather expected for the start of the work week. Shortwave
currently entering western Saskatchewan will be digging as it
approaches Lake Superior, forming a closed low over Lake Huron by
early Tuesday. This will drive a cold front southward, but general
model consensus only brings it into northern Illinois before
beginning to lift back north. The 850 mb temperatures in the
11-13C range will keep our highs above normal, with some modest
cooling on Tuesday as the front approaches. Have favored the
warmer MAV MOS guidance during this period.

Large upper low currently spinning over western Nevada still
expected to swing northeast and weaken early this week, with a small
closed low lifting through the Dakotas on Tuesday. This will help
draw the previously mentioned front back north, before a stronger
cold front moves in from the northwest. Still looks like Wednesday
will largely be dry, before showers increase Wednesday night ahead
of the front. Shear profiles increase nicely as the front gets
closer on Thursday, with 0-6km bulk shear progged to reach 40-50
knots across much of the CWA Thursday afternoon per the ECMWF model,
while the GFS is on the lower end of that range. Will need to
continue watching the threat for some stronger storms Thursday
afternoon and evening. Highest PoPs will be during the evening
hours, with a quick decrease in rain from west to east after
midnight following the passage of the front itself.

Strong surge of cooler air to plunge into the Midwest on Friday in
the wake of the front. Some model discrepancies exist at this range,
as the GFS was more prominent on driving a surface low northeast
along the front and amplifying as a significant upper low drops into
Wisconsin. The ECMWF is continues with a smaller but strong open
wave that races through the region on Friday. Both keep the coolest
air to our north, but the GFS would be more of a threat with
lingering wraparound showers. For PoPs, have continued to mention
them in the 30 to 40% range, but currently think this would
mainly be early in the morning. Temperature-wise, the GFS brings
the 850 mb zero isotherm into central Illinois by late Friday and
dipping below zero by early Saturday, while the ECMWF is already
spreading warmer air back in by that point. With this discrepancy,
the GFS would indicate highs only in the 50s on Saturday, while
the ECMWF favors mid to upper 60s. Have favored more of a blend
with Saturday as the coolest day, with highs mostly 60 to 65 degrees.


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

Used persistance for the central IL aviation forecast next 24 hours
through 18Z/Mon. Few to scattered cumulus clouds 5-7k ft this
afternoon especially from I-55 west, will dissipate by sunset at
2345Z. Otherwise patches of high clouds to occur next 24 hours
while few-scattered cumulus clouds reappear after 16Z Mon especially
from I-55 west again. Light and variable winds to prevail through
early Mon morning and then have nnw winds 3-5 kts after 16Z Monday.
1022 mb high pressure over lower MI and ridging westward into WI,
northern IL and eastern IA to remain near central IL through
Monday. This to continue fair weather through Monday as upper
level ridge extends from Texas up to IL. Patchy shallow ground fog
possible from 09-13Z along IL river at PIA where vsbys could lower
to MVFR of 5 miles.





LONG TERM...Geelhart
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