Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 150309
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
909 PM CST Wed Feb 14 2018

.UPDATE...
Issued at 909 PM CST Wed Feb 14 2018

Dense fog has already developed and will continue to spread
tonight across northern parts of the area. Have already updated to
account for the dense fog and have issued a dense fog advisory for
overnight through tomorrow at 10am. Some areas will likely improve
sooner in the morning while some areas in the extreme northern
parts of the CWA may not improve much at all, but 10am seems like
a happy middle. Since already updated once and other parameters
are looking good, no further updates are needed at this time.

&&

.SHORT TERM...(This evening through Thursday)
ISSUED AT 310 PM CST Wed Feb 14 2018

The main concern in the short term is the coverage of fog,
potentially dense fog, overnight into Thursday. High resolution
guidance is generally overdoing the amount of coverage of 1/4 mile
fog, and shows trends of the fog shifting farther north of I-74
this evening. Later tonight, areas of dense fog are forecast by
the HRRR and RAP models to expand southward into our counties, at
the same time as a band of fog expands into our southern counties,
roughly between I-72 and I-70 from Shelbyville and east. Bufkit
soundings are complicating the matter even more, showing a
potential for the fog to mainly become a very low stratus deck
instead. There remains enough uncertainty to where a dense fog
advisory would be needed, and after collaboration with
surrounding NWS offices, we will not issue a dense fog advisory
this afternoon for the tonight into Thursday period. Fog trends
will need to be closely monitored however.

Despite some brief thinning of the clouds in our SW counties this
evening, clouds should dominate the skies tonight. The blanket of
clouds along with southwest winds will help to keep low temps on
the mild side, to say the least. Lows will be near normal highs
for mid February. Areas near Galesburg will bottom out in the
upper 30s, while areas south of I-70 see lows in the lower 50s.
Lows may actually occur earlier tonight, as temps remain
relatively steady or slowly rise late. The warm temps tonight and
Thursday will go into melting quite a bit of the remaining snow
cover across our northern counties, adding fuel to the potential
for dense fog.

Highs on Thursday will have a large spread from NW to SE across
our forecast areas. That will have something to do with the path
of a surface low across north-central Illinois. It will be cooler
to the north of the track and very mild south of the track. A cold
front extending south from the surface low will progress toward
the Illinois River Valley by 6 pm Thursday. The end result will be
likely chances of rain through the day, with no thunderstorms
expected. MUCAPEs in our SE counties remain less than 100, so we
left thunder out for now. There will be a wide range of high
temps across central IL. We expect upper 40s near GBG, with mid to
upper 60s south of I-70.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 310 PM CST Wed Feb 14 2018

Thursday night, the cold front will push across the southeast half
of our forecast area. Likely rain chances should be mainly
confined to areas east of I-55, and especially east of I-57.
As the precipitation comes to an end late Thursday night, there
could be a brief transition to some light snow, but it should melt
as it hits the ground. The bulk of the cold air will arrive on
Friday and Friday night, as high pressure settles southeast from
the Plains. Some brief rain showers could linger south of I-70
early Friday morning, then dry conditions should occur the rest of
the day Friday and Friday night. Despite some sunshine on Friday,
highs will be limited to the mid 20s near Galesburg, with low to
mid 30s in the central portions of the CWA, and upper 30s south of
I-70. Lows Friday night will be the coldest of the next week, as
readings drop into the lower teens in the NW and mid 20s in the
SE.

A warming trend is forecast for Saturday through Monday,
highlighted by a warm front lifting into central IL on Monday.
High temps will climb into the upper 30s to low 40s Saturday,
reaching the upper 40s to upper 50s on Monday.

Rain chances look to be confined to Saturday afternoon in our
E-SE counties due to a low pressure system passing by to the S of
Illinois. Dry conditions look likely from Saturday night through
Sunday evening, before the approaching warm front and baroclinic
zone increase precipitation chances again. The precip type looks
to be mainly rain for Monday and Monday evening, before low
pressure and a cold front arrive and snow chances increase NW of
the Illinois river after midnight Monday night. Rain chances will
continue on Tuesday as the surface low and cold front advance east
of Illinois. Model differences in timing of that system have
caused the blended extended to contain chances of rain Tuesday
night and Wednesday, when there should be a dry period developing
at some point in that time frame.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 557 PM CST Wed Feb 14 2018

Conditions have improved in some areas but am expecting them to go
back down, especially at BMI and possibly at PIA as well. MVFR
cigs at CMI and DEC should improve to VFR later tonight, but
models indicate lower cigs will return overnight and continue
through tomorrow. SPI is VFR but lower cigs also will be
returning late overnight. PIA looks good now, but they also will
be going down to IFR and then LIFR overnight and through tomorrow.
BMI should remain IFR for several hours, but also decrease back to
LIFR overnight. Some improvement is possible late in the period as
a cold front approaches and begins to move through the sites.
Winds will be south to southwest but then become more west-
southwest ahead of the front.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST Thursday for ILZ027>031-
036>038-040>046.

&&

$$

UPDATE...Auten
SHORT TERM...Shimon
LONG TERM...Shimon
AVIATION...Auten



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