Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271157

Area Forecast Discussion
657 AM CDT Wed Aug 27 2014

.SHORT TERM...(Today and tonight)

The location of the cold front is hard to discern tonight based on
very weak wind reports and minimal dew point gradient from north to
south across central IL. Isolated showers and storms have bubbled up
in our W counties over the last 2 hours, apparently associated with
a weak 500mb shortwave. Satellite images show several shortwaves
poised to flow over the upper ridge into Illinois over the next 24
hours. Coverage and timing of any showers/storms remains a
challenge. Will continue with slight chance and low chance PoPs
generally in a west to east oriented corridor in the approximate
vicinity of the stalled out frontal boundary. Localized heavy rain
and very gusty winds will remain possible from any storm, as
evidenced with last evenings storms that dropped 3" in an hour in
localized areas from southeast of Springfield to Decatur to Clinton.
Flooding will remain a concern from any storms.

Periodic sunshine between storms today should allow for highs to
climb into mid to upper 80s south of a line from Lincoln to
Champaign. Northern areas should see lower 80s, as they remain north
of the stationary/cold front. Dew points will climb into the upper
60s north and lower 70s south, so another muggy day is in store.
Lows tonight will range from the mid 60s north to the low 70s south.


.LONG TERM...(Thursday through Tuesday)

Surface high over the Great Lakes starts to drift eastward on
Thursday, as a storm system in the Plains lifts northeast. Most of
the models show some sort of precipitation along an area of lift
extending southeast into southern Illinois, with the main focus for
MCS`s and heavy rains from Iowa northeast to Wisconsin along the
main low level jet. Will keep the southeast half of the CWA dry
during the morning before increasing the PoP`s, while healthy
chances prevail northwest of I-55.

As the upper trough chugs toward the mid-Mississippi Valley, the
cold front with this storm system will slowly push eastward. Have
trended toward a period of slight chance or no PoP`s for Friday in
the wake of an MCS moving through the Great Lakes, before ramping
them back up Friday night ahead of the front and trough. Have
increased PoP`s to the likely category (around 60%) west of I-57
during the day Saturday, and east of there Saturday night, ahead of
the cold front.

Model guidance starts to widen on Sunday with the strength of a
shortwave trough pushing through the western U.S. The ECMWF digs the
trough a bit as it pushes into the central U.S., which would bring a
shot of cooler air for early next week. The GFS keeps mainly a
west-east trough across the lower states and the wave tracking more
along the Canadian border, with hot and humid weather once again.
Have showed a slow warming trend with the temperatures next week,
though not to the extent of the GFS. Precip-wise, rain chances
should end from west to east on Sunday with the passage of the
front, then increase them again from the northwest on Monday ahead
of the next front. Have not gone as robust as the ECMWF would
suggest for PoP`s, but will have healthy chances back in the
forecast Monday night and Tuesday.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)

The stalled out cold front from west to east across the area could
provide a focus for showers and storms today and tonight. However,
numerous mesoscale boundaries from scattered convection could also
become a focus for storm initiation as well. High res models and
even the low res models are relatively quiet in terms of storms
today and tonight. There is some indication that the complex of
storms moving across N Missouri could reach our western counties
by early afternoon, and push across SPI by 21z as it curves to the
SE. A VCTS was included in all TAFs for this afternoon to account
for the thunder potential, with a front in the area and a very
humid airmass. The KILX 12z sounding showed 1400 J/kg CAPE, which
will increase with heating today providing enough instability for
convection. Very heavy rainfall and localized flooding will be
possible from any storm.
Winds will be variable early this morning closer to the front, for
SPI, DEC and CMI. In general, the terminal sites should see NE
winds today and tonight, with speeds less than 10kt.




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