Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291756
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1256 PM CDT Mon Sep 29 2014

.UPDATE...
ISSUED AT 1045 AM CDT MON SEP 29 2014

Forecast looks on track today and just a few minor tweaks done
today. Late morning temperatures are running a bit higher than
this time yesterday and may nudge highs up a bit in spots with
highs generally in the mid 80s with a few areas reaching the upper
80s with ample sunshine. The RAP/NAM curule shows few cumulus
clouds this afternoon at 5-7k ft especially from I-74 north and
western CWA while limited cumulus clouds near the Wabash river
today. Sunny skies this morning across much of IL with mostly
sunny skies expected this afternoon. Weak surface high pressure of
1018 mb over IL/MO to keep winds light again today.

&&

.SHORT TERM...(Today)
ISSUED AT 251 AM CDT MON SEP 29 2014

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)
ISSUED AT 251 AM CDT MON SEP 29 2014

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
warmer.

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 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1255 PM CDT MON SEP 29 2014

Few to scattered cumulus clouds of 5-7k ft to occur this afternoon
with broken ceilings mainly west and nw of PIA and SPI. Winds to
remain light around 5 kts or less into this evening compliments of
weak high pressure of 1018 mb over IL/MO. A cold front over
southeast WI and northwest IA will push south into central IL
during overnight, and into southern IL during Tue. Broken to
overcast stratus clouds behind the front to move to I-74 from
08-10Z and near SPI and DEC around 12Z. Have ceilings from
700-1500 feet and lowest at PIA and BMI with MVFR vsbys 4-5 miles
possible later tonight into Tue morning. Ceilings to lift to MVFR
after 15Z Tue. Models have trended further southward with stratus
clouds but vary on the cloud bases with NAM model being the lowest
below 1k ft. Winds to switch NE behind the front during overnight
around 5-9 kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...07
SHORT TERM...Shimon
LONG TERM...Geelhart
AVIATION...07





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