Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 230740

Area Forecast Discussion
National Weather Service Lincoln IL
240 AM CDT Wed Jul 23 2014

ISSUED 240 AM CDT Wed Jul 23 2014

Initial wind shift with the cold front has reached roughly along
the I-55 corridor as of 2 am, although the drier conditions lag
behind a bit with dew points still in the lower 70s northwest past
Galesburg. A warm atmosphere, with 700 mb temperatures near 13C on
on our evening sounding, and the extended effects of a strong 600
dm 500 mb high over Colorado, have largely kept the air capped
over our area. What storms managed to form didn`t do much before
fizzling. However, a more pronounced line of storms has formed
over northern Indiana and northeast Illinois, ahead of the upper
level shortwave. This line will be clipping out far northeast CWA
before sunrise.

The main forecast challenges for this package involves nocturnal
convective chances Thursday night and again Friday night.

SHORT TERM...Today through Saturday:

The front will likely be along the I-70 corridor around sunrise,
but may take much of the morning to fully clear the area. Latest
HRRR and SPC 4km WRF showing some convection redeveloping
immediately along the boundary beginning around 9 am and moving
across the southeast CWA the remainder of the morning, so will
maintain some 30-40% PoP`s in that area through noon. The
remainder of the forecast area will see north-northeast winds
spreading less humid conditions over the area. Highs across the
northeast counties will likely struggle to reach 80 degrees as the
cooler air is advected in.

Main core of the cooler air arrives tonight as 850 mb temperatures
drop to around 11C. Lows of 50-55 expected over the entire
forecast area. Currently looks like these will fall a couple
degrees shy of records in most areas. Pleasant temperatures to
continue through Thursday night.

Upper low currently off the Pacific Northwest will be tracking
northeast into the southern Canadian prairies through Thursday
night, suppressing the high in more of a west-east configuration
across the southern states. Increasing low level jet across Iowa
expected to form an MCS there Thursday evening, tracking southeast
along the 850 mb thermal gradient. The ECMWF is most progressive
with bringing the leading edge all the way to Champaign by
sunrise, but general model consensus has it still just northwest
of the Illinois River by then. Have added some 30% PoP`s for late
Thursday night in the far northwest CWA, and added PoP`s across
much of the north half of the forecast area for Friday as the
remnants of the MCS pass. Another MCS expected to form a bit
further east Friday evening over Illinois, although the NAM is
completely dry by that point. Have not made much change to the
PoP`s for Friday night and Saturday, although the highest chances
may need to be shifted a bit further east in later forecasts.

LONG TERM...Sunday through Tuesday:

The closed upper low is expected to open up into a wave over the
weekend, as the high rebuilds along and west of the Rockies. A
rather pronounced broad upper trough will prevail a good portion
of next week, with another round of cooler air similar to what
we`ll be seeing over the next 36 hours. Showers and some
thunderstorms will be possible Sunday as the wave moves overhead,
with chances after that minimal and mainly during afternoon



ISSUED 1156 PM CDT Tue Jul 22 2014

Except for a small period of time overnight when vis will be
around 5SM and cigs will be 2.5kft, MVFR, conditions should be VFR
for most of the TAF period. The front is still slowly moving
through the area, so all TAF sites could still see some
storms/showers. PIA could still see something for about an hour,
BMI and SPI for 2hrs, DEC for about 3hrs, and CMI for about 2 hrs,
though starting around 08z. Once the front goes through, winds get
light, and with low level moisture still being high, light fog
will be possible at all sites. So have 5SM BR during several hours
overnight at all sites. As is being seen at some sites, cigs
around 2.5kft could happen, but only going to have a TEMPO group
for this. Then expecting some CU development tomorrow, even though
drier air is advecting into the area tomorrow. This CU will
dissipate tomorrow evening, resulting in clear skies tomorrow
night. Winds will be southwest ahead of the front/s, but become
light; then northwest behind the front. Expecting north-northeast
winds tomorrow, with speeds around 10-12kts during the daytime hours.




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