Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 151603
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1003 AM CST Thu Feb 15 2018

.UPDATE...
Issued at 1003 AM CST Thu Feb 15 2018

Have extended the Dense Fog Advisory until 4 pm for areas from
about Canton-Bloomington northward. Warm front has continued to
lift north and visibilities south of it have reached 4-6 miles.
The melting snow north of it will continue to contribute to the
fog well into the afternoon, although the HRRR, RAP and LAMP
suggest some improvement as far north as Peoria by about 3 pm. The
cold front will be arriving during the afternoon over the
northwest CWA, and may provide some residual fog for a couple
hours immediately behind it.

Further south, temperatures are well into the 50s, with some lower
60s south of I-70. Have boosted temperatures a bit in these areas
for the afternoon.

New grids have been sent, and zone forecasts will follow shortly.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 338 AM CST Thu Feb 15 2018

Warm/moist air flowing northward over the cold ground has resulted
in widespread fog across central and southeast Illinois early this
morning. The fog has been thickest along/north of a Springfield to
Danville line where a Dense Fog Advisory is in effect until
15z/9am. The fog will tend to dissipate as showers move into the
area later this morning: however, several high-res models suggest
it will hold firm across the snow-covered northern KILX CWA
through the afternoon. Advisory may eventually need to be
extended in time, but will allow later shifts to assess trends
and make adjustments if necessary. For now, will carry fog across
the board through the morning, with fog lingering through the
balance of the day along/north of a Rushville to Bloomington line.

1004mb low currently over northern Kansas will track E/NE across
north-central Illinois today, resulting in increasing rain
chances. Forecast soundings indicate modest MUCAPE of 100-200J/kg
and the HRRR has been consistently showing scattered convection
developing across west-central Illinois by 12z/13z...then quickly
tracking eastward to the Indiana border by midday. Have therefore
added isolated thunder to the forecast. High temperatures today
will range from the lower to middle 40s north of the low track
around Galesburg and Lacon...to the middle 60s south of I-70.

As the low tracks into the southern Great Lakes, it will drag a
cold front through the area tonight. With continued modest
elevated instability along/south of the boundary and both the
WRF-ARW and WRF-NMM hinting at convection, have continued isolated
thunder along/south of a Champaign to Taylorville line this
evening. Once the front settles into the Ohio River Valley, the
showers will come to an end across the SE CWA by early Friday
morning.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 338 AM CST Thu Feb 15 2018

Cool/dry weather will be on tap for Friday...courtesy of high
pressure building into the Midwest. Highs will drop into the 30s,
with middle to upper 20s across the north. After a cold/dry night
Friday night, the next short-wave trough will quickly skirt
through the area on Saturday. This feature will have limited
deep-layer moisture to work with, so have kept PoPs on the low
side. May see some light snow briefly as the precip begins, but it
will quickly transition to all rain as temps rise into the 40s.
Once this wave exits, a return to mild/dry weather is anticipated
for Sunday.

After that, the weather pattern turns active early next week...as
southwesterly flow establishes itself across the central/eastern
CONUS. The 00z Feb 15 models are in very good agreement concerning
the first system progged to track through the prevailing
flow...with both the GFS and ECMWF tracking a surface low from the
central Plains into the Great Lakes on Monday. This places central
Illinois firmly in the warm sector, with numeric guidance
suggesting highs soaring well into the 60s and perhaps even
reaching 70 degrees across the south. It also sets the stage for
widespread showers and a few thunderstorms as instability
increases ahead of the low and its trailing cold front. Have
therefore added isolated thunder to the forecast Monday afternoon
through Tuesday. There are some discrepancies concerning the speed
of the departing system and whether or not another surface wave
will develop along the front and bring more rain to the area into
Wednesday. Based on model trends, decided to limit further rain
chances to the S/SE CWA on Wednesday...with dry weather returning
elsewhere.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 544 AM CST Thu Feb 15 2018

IFR ceilings/visbys prevail at the central Illinois terminals this
morning. As southerly flow increases, the fog is expected to
gradually lift northward...with the latest HRRR showing visbys
improving to P6SM at KSPI/KDEC by mid to late morning and at KCMI
by around midday. Further north, dense fog will likely hold firm
at KPIA through midday before slowly dissipating this afternoon.
Ceilings will rise to MVFR at KSPI/KDEC after 16z...but will not
improve at KBMI/KPIA until after 22z. Latest radar imagery is
showing showers developing upstream across Missouri...and these
are expected to push through central Illinois later this morning.
Have therefore included TEMPO groups for SHRA at all sites between
13z and 17z. Winds will initially be S/SW at 10-15kt today, then
will veer to the W/NW and gust 20-25kt late tonight into Friday
morning.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 4 PM CST this afternoon for ILZ027>031-
036>038.

Dense Fog Advisory until 10 AM CST this morning for ILZ040>051-
053.

&&

$$

UPDATE...Geelhart
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Barnes



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