Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 270820

Area Forecast Discussion
320 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 06Z TAFS through 06Z Wednesday night)

Predominantly VFR aviation weather conditions expected across the
central Illinois terminals through the 06Z TAF valid time. Still
looks like a brief period of MVFR fog is possible later tonight,
although the convective debris cloud in the area make this a
little less certain than it seemed earlier tonight. Precipitation
for the period is likely to be quite tricky. Feel the bulk of the
night should be dry, and much of Wednesday may be as well.
However, with a weak cold front slipping south through the area,
and/or the presence of outflow boundaries, and expected arrival of
a weak upper wave Wednesday, feel a mention of VCSH or VCTS if
warranted. Confidence in timing of any precipitation is too low to
go with a tempo or predominant period. If convection were to
impact a terminal directly, lower than VFR conditions are
possible. Winds through the period should be light/variable away
from any convection with weak boundaries in the vicinity.




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