Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 282011
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
311 PM CDT Mon Jul 28 2014

.DISCUSSION...
ISSUED 300 PM CDT Mon Jul 28 2014

An extended period of below normal temps is on tap this week as a
long wave trough dominates the eastern half of the CONUS.
Shortwaves in the northwest flow aloft will combine with steep
mid-level lapse rates in the cooler air to produce afternoon and
evening shower/storm chances through the week.

SHORT TERM...Tonight through Wednesday night.

Surface high pressure centered from the Dakotas to Oklahoma will
gradually build southeast into Illinois over the next couple of
days. A progressive surface low in the northeast states will lift
into Canada tonight, but additional low pressure in NE Ontario
will rotate toward the Great Lakes in its wake on Tuesday. Time-
height cross-sections over the next week show a layer of moisture
persisting in the 800-900mb layer into next weekend.

Diurnal cumulus this afternoon were somewhat thicker in our
eastern and southern areas as a weak surface trough moved south
into Kentucky. Better vertical cloud development remained west of
Illinois in Iowa, where a few radar returns may have indicated a
brief shower or sprinkles. Clouds in our forecast area should
continue their diurnal trend and dissipate shortly after sunset.

With expectation of mostly clear skies and light winds tonight, we
undercut guidance lows slightly and went with low to mid 50s
across the board. It will be out coldest night of the week as
850mb temps remain in the 9C-11C range. The coldest air will
remain centered east of Illinois.

Tuesday will bring a return of low rain chances across northern
Illinois and as far south as Bloomington to
Champaign/Danville...as upper level energy and the cold pool
trigger a few showers. Thunder chances will remain very low. A
warming trend is expected in overnight lows as 850mb temps climb a
few degrees by Tue night.

A stronger shortwave just southwest of Illinois on Wednesday
prompted the expansion of the slight chances of rain farther
southwest across the remainder of our forecast area. The 12z model
guidance had better agreement of a more active shower pattern in
IL mainly associated with a trough rotating south of Lake
Michigan, but with possible increased synoptic scale forcing from
the wave SW of IL.

LONG TERM...Thursday through Monday.

Extended model output for Thursday showed a trough axis
progressing into Illinois around the longwave trough. That usually
is associated with additional cold air and shortwave energy, but
the models were not indicating much of either one during that time
frame. Therefore we kept PoP down in the slight chance category on
Thursday.

Friday had much better agreement in the GFS, ECMWF and Canadian
Global for a stronger piece of energy rotating across IL. Chance
PoPs for rain and storms were included across the board. Updraft
strength looked more favorable for ice development and subsequent
lightning production. Similar chances for precip were included on
Saturday as the upper trough is forecast to sharpen across Indiana
and keep much of Illinois in the thermal trough.

Upper level ridging is projected for Sunday and Monday, which
should coincide with an end to the daily precip chances, and a
slight warming trend in highs and lows, but still below normal.

Shimon
&&

.AVIATION...
ISSUED 1227 PM CDT Mon Jul 28 2014

VFR conditions will prevail through the entire 18z TAF period.
Latest visible satellite imagery shows mainly scattered diurnal
clouds across central Illinois: however, a more concentrated area
is noted east of a KBMI to KDEC line. As a result have included a
2-hour TEMPO group for MVFR ceilings at KCMI early this afternoon.
Clouds will rapidly dissipate toward sunset, with clear skies
expected overnight. Brisk N/NW winds will continue through the
afternoon hours, with occasional gusts to around 20kt. Atmosphere
will decouple after sunset, resulting in light/variable winds
overnight. After that, NW winds of around 10kt will resume Tuesday
morning.

Barnes
&&

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

$$







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