Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 211547

Area Forecast Discussion
National Weather Service Lincoln IL
1047 AM CDT Mon Jul 21 2014

ISSUED 1043 AM CDT Mon Jul 21 2014
High pressure ridge axis slipping eastward and increasingly
southerly return flow pushing warmer and more humid air into the
region. Wind speeds picking up a bit as the pressure gradient
begins to increase...with lighter and slightly more variable winds
in the east. Expecting some cu to develop yet again today, but
will not do much for the warming trend and forecast is on track
for the mid to upper 80s for the max temps. No update anticipated
at this time.


ISSUED 700 AM CDT Mon Jul 21 2014

MVFR fog will linger around CMI through 13z then dissipate to VFR
vis. Any other vis reductions for the other TAF sites should
remain VFR at 6SM BR. The surface ridge axis in the Ohio River
Valley will slowly move east today, allowing more southerly flow
to develop across central IL. South winds will increase to around
10kt at the terminal sites, then decrease again by evening.

Cloud development today will be mainly in the 4-5K ft layer, with
very few periods of ceilings becoming BKN.

MVFR light fog could develop again late tonight around CMI,
possibly down to 4SM BR after 10z/5am.


ISSUED 255 AM CDT Mon Jul 21 2014

Stagnant weather pattern continues across the area, with just some
cirrus dropping southward early this morning. Had a rather
pronounced smoke layer also moving southward through the state
yesterday, but latest status is unknown as it was only tracked
via visible satellite imagery which is currently dark. Similar to
this time yesterday, have had some shallow dense fog across mainly
the far eastern CWA, closer to the lingering ridge axis. Aloft,
high pressure over New Mexico continues to build northward through
the central Plains, tracking any shortwaves well to our north
along the periphery of the ridge.

The main forecast concern remains with rain chances Tuesday night
and Wednesday with the passage of a cold front.

SHORT TERM...Today through Wednesday:

Beginnings of our cold front is taking shape to our west, with low
pressure over central South Dakota and a trailing cold front
extending into Colorado. The front is expected to cross the
forecast area late Tuesday night and early Wednesday. The
atmosphere ahead of this front should be rather capped on Tuesday,
as 700 mb temperatures rise to around 14C northwest of I-55, and
there is some question as to how fast it will break during the
evening. Have removed the slight chance PoP`s during the day
northwest of the Illinois River, and kept a narrow axis of likely
PoP`s Tuesday night to about I-55. Am hesitant to introduce it
further east for now due to the uncertainty as to whether the cap
fully breaks. Severe weather threat looks marginal, with very weak
shear ahead of the front and the aforementioned cap issues. Much
of the rain should be out of northwest half of the forecast area
by midday Wednesday, but will likely linger for a time into the
afternoon across the southeast half.

Temperature-wise, the heat and humidity will continue to slowly
build through Tuesday. Lower 90s will be common on Tuesday, with
the highest heat index values west, around 100-102. Cooler air
will start to plunge southward on Wednesday as an upper trough
deepens overhead, and highs may struggle to reach 80 north of

LONG TERM...Thursday through Sunday:

The strong upper high should flatten some late week, as a closed
low deepens over the Pacific Northwest and rides along the top of
the ridge. Will see a day or two of more pleasant conditions with
highs near 80 and lower humidity, before slightly warmer and more
humid conditions return for the weekend. However, this will be
short lived, as the pattern for next week returns to cooler than
normal temperatures again.

High pressure to dominate Thursday and Friday with fair
conditions, then concern shifts to potential MCS activity as a
weak shortwave tracks in from the Dakotas. Not much model
agreement in the details that far out, with the GEM mainly to our
southwest, the ECMWF splitting it around us, and the GFS affecting
us most. Have not made a lot of changes to the PoP`s yet as a
result, but there will probably be a period of drier weather on
Sunday as weak high pressure moves in temporarily.




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