Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201740
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1240 PM CDT Mon Oct 20 2014

.UPDATE...
ISSUED AT 1029 AM CDT MON OCT 20 2014
Weak low pressure over the Great Lakes with the trof axis/weak boundary reaching
back across ILX this morning. Very narrow line of showers
developing with some assist from the low level jet this morning
over east central Illinois along the Indiana border. Northwesterly
flow dominating the state today with plenty of sunshine warming
temps up to near climate normals. Some minor tweaks to sct cloud
cover through the afternoon... but no large scale changes to the
forecast anticipated at this time.

&&

.SHORT TERM...(Today)
ISSUED AT 229 AM CDT MON OCT 20 2014

Latest surface analysis had low pressure centered over eastern Lake
Superior, with the trailing cold front extending southwest into the
central Plains. This low/front is being driven by a potent short
wave diving southeast across the upper Midwest/western Great Lakes.
However, despite the good forcing these features should provide, the
air mass the system is moving through is very dry. In fact, at the
moment, there is little/no cloud cover along the cold front once you
move away from the immediate vicinity of the surface low. There is
respectable WAA/isentropic lift over the southeast 1/3 of Illinois
ahead of the cold front, and this is resulting in a few sprinkles
breaking through from time to time from an AC deck around 10k feet.
This enhanced warm advection regime should shift south/east of the
forecast area by shortly after sunrise. So, do not expect measurable
rainfall ahead of the front today, although a few sprinkles will be
possible south of I-70 into the mid-morning hours.

The cold front should have cleared the forecast area by early
afternoon, with temperatures staying steady or slowly falling in its
wake. A strong low level inversion that is currently in place should
quickly erode in the post frontal cold advection. This may result in
a few hours of gusty northwest winds this afternoon.

&&

.LONG TERM...(Tonight through Sunday)
ISSUED AT 229 AM CDT MON OCT 20 2014

Once the current system passes, the remainder of the week looks to
be fairly quiet. The upper ridge currently along the east slopes of
the Rockies will shift eastward into the Mississippi Valley by mid
week, with dry weather prevailing. The main forecast issue involves
Thursday, as the ridge erodes between an incoming wave from the
northern Plains, and a large upper low that will slowly wobble
through the mid-Atlantic states. The general consensus over the last
few model runs was that the associated shower activity would have
difficulty crossing the Mississippi River into Illinois, but the
latest GFS and ECMWF do bring some diminishing showers across the
north half of the state Thursday afternoon/evening as an upper low
develops and slides into northern Wisconsin. Have kept the forecast
dry for now, but will monitor to see if this is a persistent trend
before introducing into the forecast.

A nice warming trend is on tap toward late week, as thermal ridging
extends east from the central Plains. 850 mb temperatures progged to
rise to around 16C by Saturday afternoon, which would bring surface
temperatures to around 70 degrees in many areas.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1237 PM CDT MON OCT 20 2014

Northwesterly flow today with clear skies becoming more northerly
by morning. Light and somewhat variable in the overnight. Some
moisture in the low levels may develop into some sct clouds...with
more bkn deck to the north and northeast. Some concern that the
shortwave over the upper Midwest would dive into the region and
threaten ILX terminals with a more bkn deck. NAM is the only one
showing enough moisture to cover CMI and BMI...other models drier,
including the HRRR. For now, will maintain the SCT mention, though
later issuances may require a bkn deck for CMI and BMI.

&&

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

$$

UPDATE...HJS
SHORT TERM...Bak
LONG TERM...Geelhart
AVIATION...HJS





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