Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 011204
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
704 AM CDT Wed Oct 1 2014

.SHORT TERM...(Today)
ISSUED AT 258 AM CDT WED OCT 1 2014

The upper-level ridge of high pressure that has brought much above
normal temperatures to the Midwest over the past several days will
slowly lose its influence today as a long-wave trough over the
western half of the CONUS begins to translate eastward.  07z/2am
water vapor imagery shows a series of short-waves embedded within
the parent trough, with a lead wave currently ejecting into
western Kansas/Nebraska and another wave further upstream over the
Great Basin.  The first wave will lift N/NE today, remaining well
west of Illinois.  As a result, convection associated with this
feature across eastern Kansas into central/western Iowa will track
mainly northward into Minnesota/Wisconsin as the day progresses.
Some models are suggesting that precip may reach the far western
KILX CWA by late afternoon: however, given dry airmass initially
in place and a continued easterly component to the wind, think
this is a bit too aggressive.  Will therefore go with a dry
forecast across the board today.  Skies will start out mostly
sunny, with a gradual increase in cloud cover during the afternoon
west of I-55.  Thanks to the sunshine and winds veering to the
southeast, high temperatures will reach the upper 70s and lower
80s.

&&

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 258 AM CDT WED OCT 1 2014

Initial short-wave will pass to the W/NW of Illinois this evening,
while Great Basin feature ejects into the Plains and induces surface
cyclogenesis over the Texas/Oklahoma panhandles.  As this low begins
to lift N/NE and airmass moistens, showers and thunderstorms will
develop across west-central Illinois during the evening then spread
eastward toward the Indiana border by Thursday morning.  With best
forcing associated with the second wave remaining to the southwest
and forecast soundings still showing a dry layer below 850mb, have
opted to reduce PoPs to just chance along/west of I-55 this
evening.  Think better rain chances will arrive mainly across the
western CWA after midnight, with areas further east near the Indiana
border likely staying dry through the entire night.

Low pressure over Oklahoma Thursday morning will track northeastward
into Wisconsin by Thursday night.  As it does, it will drag a strong
cold front through central Illinois.  Models have been trending
slightly slower with the front, with most solutions now showing
FROPA overnight Thursday.  With strongest forcing for convection
staying to the west near the low and associated front, have focused
highest PoPs in the likely category across the western half of the
CWA on Thursday with only chance PoPs along/east of I-57.  Will be
another warm day with highs ranging from the middle 70s far
northwest around Galesburg to the middle 80s along/south of I-70.

Main convective event still appears to be on track for Thursday
night as front interacts with an unseasonably moist airmass
characterized by precipitable water values in excess of 1.50.  Given
ample deep-layer moisture and strong upper dynamics, will carry
categorical PoPs across the board.  Latest Convective Outlook from
SPC suggests the potential for strong to severe storms Thursday
evening as a squall line develops along/ahead of the front.

Front will sweep into Indiana by Friday morning, with a few
lingering showers possible across the Wabash River Valley early in
the day.  Main story on Friday will be the windy and much cooler
conditions.  Due to a tightening pressure gradient and adequate
mixing, W/NW winds may gust to around 30mph at times.  High
temperatures will mainly be in the 60s.  An upper wave digging
southward out of Canada may trigger scattered showers across the
region Friday afternoon/night.  Timing discrepancies still exist
among the models, so will only mention slight chance for showers
Friday night at this time. Once this feature passes, very cool and
dry conditions are anticipated this weekend.  Coolest day will be
Saturday when highs will remain in the 50s and overnight lows will
dip into the upper 30s.  After that, northwesterly flow will
prevail through the middle of next week, resulting in a
continuation of below normal temps.  Airmass modification will
allow temps to slowly climb back into the upper 60s by Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
ISSUED AT 700 AM CDT WED OCT 1 2014

Expect VFR conditions all day today with increasing high clouds
this afternoon as showers and storms advance gradually eastward
across N Missouri and E Iowa. That initial wave will primarily
lift toward S Wisconsin, with residual lift moving east into
western Illinois. Showers and storms should hold off near the
terminal sites until 02z for PIA and SPI, advancing slowly east
toward CMI after 09z. The best chances for steady rains will be
for PIA and SPI late tonight where synoptic scale lift appears to
be strongest in time-section analysis. MVFR clouds could develop
once the showers and storms reach any TAF site, but we kept VFR
clouds for now.

Winds will remain primarily southeast today in the 7 to 12kt
range. The cold frontal passage is not expected until Thursday
evening, so south to southeast winds will continue for much of the
next two days.

&&

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

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon






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