Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 190444

Area Forecast Discussion
National Weather Service Lincoln IL
1144 PM CDT TUE OCT 18 2016

Issued at 902 PM CDT Tue Oct 18 2016

The cold front will continue to make steady progress to the
southeast overnight, with a few light rain showers possible along
and ahead of the front. Have continued with slight chances of rain
for our southeast counties, mainly SE of I-70 as the front
approaches Effingham to Terre Haute at 9pm. Mainly clear skies and
light northwest winds behind the front has allowed Galesburg to
drop to 56 already this evening. Have adjusted low temps downward
a couple degrees for areas NW of the IL river, with less
adjustments in low temps from I-55 and east.

The front is slowing down in its forward progression, which
matches with the HRRR and RAP guidance that shows the front
stalling out along the southern Indiana state border. That will
leave the front close enough that the next shortwave to ride NE
along the front will bring increasing chances of showers in our
forecast area during the day tomorrow, especially tomorrow
afternoon. That is handled well in the current forecast grids.
Updates for the evening with done to low temps, dewpoints,
weather/PoPs, and sky conditions. The latest info is already


.SHORT TERM...(This evening through Wednesday)
ISSUED AT 255 PM CDT Tue Oct 18 2016

A cold front will continue to drift south over the forecast area
this evening, with a band of lower clouds just ahead of it...and a
slight chance for rain and thunder in the southeast this evening.
Cooler air filtering in behind the boundary will result in overnight
lows in the 50s north of the I-70 corridor...low 60s south.  This
same boundary stalls in the region, near the Ohio River
valley/southern borders of the state later tonight.  Small waves
rippling through the region bring a chance for showers along and
behind the boundary through the southern half of the state for
Wednesday. Models differing somewhat with the northern extent of the
showers through tomorrow afternoon before the bulk of the
wave/precip develops for the evening hours.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 255 PM CDT Tue Oct 18 2016

The cold front moving through central Illinois early this afternoon
is expected to slow down as it becomes parallel to the upper level
flow near the Ohio River Valley later tonight. A shortwave, seen on
water vapor imagery approaching the Rockies, is expected to approach
just west of the MS River Valley Wednesday evening. This will be
provide upper level support for showers and t-storms in parts of
central and southern Illinois - mainly south of a Springfield to
Danville line. Many of the models continue to show mainly elevated
storms north of the surface boundary, however south of I-70 CAPEs
are higher and wind shear sufficient for a few storms to become
strong or even severe with hail and wind gusts during the evening.

The GFS and European are similar with the timing and intensity of
the deepening upper level trough as the western shortwave moves east
of the MS River Valley Thursday. The NAM and Canadian are a bit
slower and are holding on to the rain longer into Thursday afternoon-
early evening. Prefer the quicker GFS/European blend and will only
hold on to lingering showers near the Indiana border Thursday

High pressure and a northwest upper level flow will allow
temperatures to drop toward more seasonable levels for Friday and
through the weekend. Will hold off on mentioning patchy frost for
Friday morning north of I-74 with temperatures in the upper 30s and
northwest winds around 5-10 mph.

After several days of dry weather through the weekend and into early
next week, the next shot at showers may be next Tuesday. The GFS has
warm front draped across parts of central IL. However, there is
fairly low confidence with this solution since the GFS Ensembles are
all over the place, and the inconsistent European is showing dry
weather. Thus, will only introduce a chance of showers near the
potential frontal boundary location around the Peoria area and to
the northwest.


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1144 PM CDT Tue Oct 18 2016

The cold front and all associated light rain showers continue to
drift farther south of I-70 this evening. Winds have continued to
veer from NW toward N, and will eventually become NE before
sunrise. A generally weak pressure gradient is expected during the
next 24 hours, as high pressure builds into Illinois from the
west. Winds should remain NE through the day tomorrow, with speeds
generally remaining less than 10kt.

The cold front will stall out roughly along a line oriented along
the southern border of Indiana late tonight, then begin a slow
shift back northward tomorrow afternoon in response to a weak
shortwave lifting NE along the front. That will bring increasing chances
of showers into central and SE IL. Showers and a few storms will
become likely by evening for SPI, DEC and CMI with chances
including PIA and BMI through the evening. Storm chances should
generally remain south of I-72, but we included VCTS for SPI, DEC
and CMI for the evening time frame to coincide for the passage of
the low pressure to the south of our counties. In general, we kept
prevailing conditions in the VFR category for this TAF period,
but any storms could produce MVFR cloud heights or visibility for
short periods of time if they move over any terminal sites
tomorrow evening.


.ILX Watches/Warnings/Advisories...


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