Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 252003

Area Forecast Discussion
National Weather Service Lincoln IL
303 PM CDT Tue Apr 25 2017

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 303 PM CDT Tue Apr 25 2017

Gusty south winds will continue into this evening, as a cold front
approaches from the west. Low level moisture will be on a steady
increase tonight, with the cold front expected to reach near the
Mississippi River by 12z/7am Wednesday. Scattered showers and a
few thunderstorms will be possible late tonight, mainly west of
the Illinois river, but possible as far east as the I-55 corridor.

Better chances of rain will begin Wednesday afternoon as the cold
front pushes to near I-55. Instability and wind shear parameters
look favorable for some severe storms to develop late Wed
afternoon, with damaging winds the primary threat, and large hail
also possible.


.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 303 PM CDT Tue Apr 25 2017

The extended forecast will start out Wednesday evening with a
squall line moving from SW to NE across central Illinois, roughly
along the I-72 corridor. The NAM is even hinting at multiple
squalls training over the same areas, which would ramp up the
potential for flash flooding. Instability appears to drop off by
03z, so severe threat should be mainly from late Wed afternoon to
mid evening.

The cold front will push into Indiana by sunrise on Thursday, but
showers are expected to linger Thursday morning. Dry conditions
should return for Thursday afternoon as cooler air arrives on NW
winds. Highs will be limited to the upper 50s and low 60s, or
about 15 to 20 degrees cooler than Wednesday`s highs.

Attention then turns to an extended period of wet weather from
Friday through Sunday night. The first wave or rain looks to
arrive Friday morning and continue through the day. There are some
model differences as to the location of the warm front as a
shortwave moves across southern Illinois. The better chances of
heavy rainfall appears to set up after midnight Friday night and
continue through Saturday night. The system will be driven by a
deepening upper level trough in the Plains on Friday, with a
surface low eventually ejecting into far NW Illinois by Sunday
afternoon. Copious amounts of moisture are projected to surge into
Illinois ahead of the system as it occludes and slowly drifts
northeast toward the western Great Lakes this weekend. While the
potential for severe storms in Illinois will be marginal, several
periods of heavy rainfall could push rainfall totals between 2 to
4 inches in much of central and southeast Illinois. The highest
totals look to be along and south of I-70, but model adjustments
over the next few days should provide better clarity on the axis
of heavy rainfall.

We continued the Hydrologic Outlook for the potential for heavy
rainfall and flooding with the combination of locally heavy rains
Wednesday/Wed night in addition to the heavy rains Friday through
Saturday night. While showers continue on Sunday under the
occluding low, the potential for heavy rains should diminish by
Sunday morning as dry air wraps into the upper low, leaving a more
shallow saturated layer.

Dry conditions should close out the extended forecast for Monday
and Tuesday. Monday will be noticeably cooler, with highs similar
to Thursday, in the upper 50s to low 60s. A warming trend will
develop for Tuesday, as increasing sunshine helps boost high temps
into the upper 60s to around 70.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 100 PM CDT Tue Apr 25 2017

VFR conditions should prevail the rest of today and this evening
as high clouds drift across Illinois ahead of approaching low
pressure. Winds will remain the primary concern this afternoon as
south winds gust to 25kt at times. Some gusts to near 20kt could
even linger several hours this evening, based on momentum transfer
plots in bufkit. High resolution guidance are generally agreeing
that storms will hold off until after midnight. PIA could see
storms as early as 07z, but trends have been to slow down the
arrival of precip in general. Have introduced a VCSH to start at
PIA at 09z, with VCTS around 12z. Most of thunder potential should
hold off at the other terminal sites until after 12z, as the
best forcing for precip remains west of I-55 until later morning.
Some brief MVFR conditions could develop as the storms reach near
a TAF site. However, prevailing cloud heights should remain low




LONG TERM...Shimon
AVIATION...Shimon is the U.S. government's official web portal to all federal, state and local government web resources and services.