Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 210547
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1147 PM CST Tue Feb 20 2018

.UPDATE...
Issued at 910 PM CST Tue Feb 20 2018

The cold front is making steady progress through our southeast
counties, and should exit our forecast area by midnight. In its
wake, steady rains are affecting the majority of our forecast
area southeast of the Illinois river. NW of the IL river, temps
are dropping below freezing, with freezing rain just being
reported at Peoria at 9 pm. Some light snow is also being reported
upstream in Macomb, while Galesburg is not reporting precipitation
anymore. So the period of precipitation after rain changes to
freezing rain seems to be narrowing. Icing from freezing rain may
be limited to elevated surfaces, bridges, overpasses, and on/off
ramps. Change-over to snow seems to be very limited as well, based
on upstream observations. After precipitation ends from NW to SE,
re-freezing of residual and standing water could cause travel
difficulties for the morning commute, mainly N of I-70. Will
continue with winter weather advisories as posted, as some areas
could see travel hazards overnight as temps fall. May be able to
remove counties early in our NW areas as precip comes to an end.

The other concern is Flash Flooding, especially in areas that saw
rains earlier this week in our central and NE counties. Have a
flash flood warning in effect until 115 am for several counties
due to reports of roads covered with water and more rain
occurring.

Updates this evening were to adjust the faster onset/change-over
to freezing rain. The remainder of the forecast looks relatively
on track. Updated forecast info is already available.

&&

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 259 PM CST Tue Feb 20 2018

Cold front has recently passed through Decatur, and will arrive
soon in Champaign. Temperatures initially behind it fell 22
degrees in Peoria in 5 minutes, but more recently the drop has
been more in the order of a slower 15 degree fall. With a steady
fall through the evening, most areas west of I-55 should be in the
mid 30s or colder by midnight. Unfortunately, the rain won`t be
done by this point, as more precipitation continues to surge
northeast out of Missouri. Forecast soundings show a prominent
warm nose around 2,000 feet lingering much of the night, so a
changeover to freezing rain and some sleet remains likely. This
should begin this evening west of the Illinois River, and near
I-55 toward the midnight-2 am time frame. Accumulations of around
a tenth inch appear likely on elevated surfaces. Road conditions
may be a bit of a question mark, with the warm pavement from
today, but some travel impacts are still expected. As a result, a
Winter Weather Advisory will be issued for most of the forecast
area. Exception is from about Danville-Effingham southeast, where
the precipitation should be ending around the time temperatures
get cold enough.

In terms of the flooding potential, the Flood Watch will be
expanded into the southeast CWA through tonight. Areas along and
south of I-70 have been missing out on the heaviest rain so far,
but 1-2 inches appear reasonable as precipitable waters remain
around 1.5 inches past midnight. The flood threat west of I-55
will be diminishing, but will leave that part for now and let the
next shift continue to monitor for several more hours.

For Wednesday, the cold front will be hanging up across the
Tennessee Valley into southern Arkansas, with another surge of
moisture coming northeast with a shortwave. Thus, will keep PoP`s
going through the day south of I-70.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 259 PM CST Tue Feb 20 2018

Some variation among the models among exactly how far north this
next moisture surge moves up, but they continue to suggest a
west-east corridor of some freezing rain Wednesday night into
Thursday. Currently this is more favored between I-72 and I-70,
but could reach as far north as Peoria by early Thursday before
transitioning to rain.

With the southwest upper flow persisting through late week, the
next storm system still on track to arrive Thursday night. Waves
of low pressure will continue to ride northeast, until the final
passage of the system Saturday night. Latest ECMWF was not
available for comparison, but the new GFS was much stronger than
the old European run, though timing was in reasonable agreement.
The southeast CWA is more on track for any significant rainfall at
this time, and with the ground saturated from the current system,
another round of flooding will be possible.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1147 PM CST Tue Feb 20 2018

The cold front continues to advance E-SE of the TAF sites, with
NW wind gusts diminishing to 20KT or less. Moderate to heavy rain
is mainly east of I-57 as of 0530Z/1130 pm, with some IFR
ceilings at BMI and CMI. Otherwise, flight categories have
improved to MVFR at SPI, and DEC and VFR at PIA. Potential for
periods of IFR due to low clouds and vis will continue for all but
PIA TAF sites until precipitations nears an end, when MVFR and
possibly VFR clouds develop. Freezing rain and icing will be the
other main concern the rest of the night. Temps will drop below
freezing at all terminal sites after midnight, with some light
freezing rain and sleet/snow possible for several hours before
precipitation ends from NW to SE between 07z (PIA) and 12Z (CMI).
Despite how much freezing rain/icing occurs during the
precipitation, travel surfaces could still re-freeze due to
residual water on the ground. Slippery travel is expected as the
night progresses.

NW winds should diminish below 10kt tomorrow morning, with clouds
improving to VFR. Winds will shift to the NE by later afternoon,
with speeds of 10-14kt.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 6 AM CST Wednesday for ILZ029>031-036>038-
040>057-061>063-066>068-071>073.

Winter Weather Advisory until 6 AM CST Wednesday for ILZ027>031-
036-037-040-041-047-049-050.

Winter Weather Advisory until 6 AM CST Wednesday for ILZ038-
042>045-048-051>055-061.

&&

$$

UPDATE...Shimon
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Shimon



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