Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 142110

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

.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

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 18Z TAFS through 18Z Thursday afternoon)
Issued at 1205 PM CST Wed Feb 14 2018

Locally dense fog will linger near BMI and CMI this afternoon, as
the boundary layer remains near saturation. A stationary boundary
extending from the west into west-central Illinois seems to be
becoming a focus for our fog and low clouds. Weak lift in a broad
area seems to be just enough to expand our low clouds and fog
formation, along with some areas of drizzle. HRRR and RAP updates
show visibility at or below 1/4sm mainly across our northern
counties, and drifting north later this afternoon. However, they
also indicate the dense fog potential and VLIFR conditions should
expand back southward tonight, including areas east of I-55 down
to I-70. Have not included widespread VLIFR conditions with the
18z TAFs, but may need to add that as more data analysis is

Most of the terminal sites should remain IFR or LIFR due to
clouds, with brief MVFR possibly around SPI as a narrow corridor
of dry air advances into our SW counties later this afternoon and

Showers will expand in coverage tomorrow morning as low pressure
progresses from west to east across north-central IL. Have
included prevailing rain in the last 3 hours of this TAF period as
a result.




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.