Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200258
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
858 PM CST Thu Jan 19 2017

.UPDATE...
Issued at 854 PM CST Thu Jan 19 2017

Have had to adjust PoPs across the area for the rest of the night.
Steady rains continue to fall across eastern 1/3 of the forecast
area, and this should linger for at least several more hours. In
addition, another impulse rotating around the large Plains upper-
level low is producing showers and even a few thunderstorms across
Missouri. This disturbance will spread measurable rainfall further
west across the forecast area than previously anticipated later
tonight. Drizzle/fog will persist between showery periods through
the night. Otherwise, only minor hourly forecast tweaks were
needed.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 245 PM CST Thu Jan 19 2017

Initial rain shield continues to advance northward across the CWA
this afternoon, but already is tapering some across southern
Illinois. Radar mosaics showing additional light rain tracking
northeast out of Arkansas, and this will surge northeast as a weak
surface low develops and tracks into southeast Illinois around
midnight. Thus, will keep categorical PoP`s >80% going over the
east/southeast CWA a good chunk of the night, before the low finally
lifts northeast.

West half of the CWA will see the precipitation diminish to drizzle
this evening, as drying starts to take place above 900 mb. Low
levels remain very saturated through the night though, and winds
will become nearly calm behind the low. With the low level moisture
not going anywhere, think that dense fog will become a concern,
especially after midnight, and will issue a Dense Fog Advisory for
areas west of I-57, running from late evening into the first part of
Friday morning. The fog should start to lift somewhat, but may
persist into the afternoon as a warm front begins to take shape over
central Illinois.

Despite the extensive clouds on Friday, the warmer air surging in
south of the front should help boost temperatures into the 50s in
many areas.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 245 PM CST Thu Jan 19 2017

A warm front will be tracking north across the forecast area Friday
night accompanied by some low chance POPs/drizzle and fog, with
the threat shifting north of our area late Friday night or early
Saturday as the front edges to our north by morning. This will set
the stage for an unseasonably warm day on Saturday just ahead of
the next weather system that looks to be tracking well south of
our area on Sunday. Shower chances Saturday afternoon through
Saturday night will be confined mainly to the eastern half of the
forecast area with even the possibility for a thunderstorm as
MUCAPE values range from 250-400 j/kg during this time frame over
east central and especially southeast Illinois.

By Sunday, it appears as if central Illinois will be in between two
significant areas of lift, one being well to our north over the
upper Great Lakes, with the second upper system and surface low
tracking well south of the Midwest. With that scenario looking more
likely, it appears the better chances for rain will occur north and
south of our area. As a result, will continue to pull back some on
rain chances Sunday, especially across the west and north, with
the latest ECMWF keeping any measurable rainfall confined to the
I-70 corridor, while the GFS was a bit further north and west with
the rainfall for Sunday. Areas along and south of a Rushville to
Bloomington line will have the higher POPs, ranging from 30 north
to near 50 over southeast Illinois.

Rain chances will slowly decrease later Sunday night through Monday
as the southern storm system moves well off to our east. The good
news into the middle portion of next week is that temperatures
will continue to average above normal with the flow pattern over
the middle of the country remaining west to southwest. A more
potent storm system will take shape to our west on Tuesday and
bring low pressure into western Iowa by Tuesday evening. This
should once again draw mild air north ahead of the storm system
during the day Tuesday with models indicating 850 mb temps of +4
to +8 degrees which should produce highs Tuesday afternoon of 45
north to around 50 over southeast Illinois. The better rain
chances with the mid- week system should arrive by Tuesday evening
with lingering precip chances across the north late Tuesday night
through Wednesday.

As the surface low shifts off to our north and east Wednesday
afternoon and evening, colder air will be able to be pulled south
into the region by the end of the week as a deep upper level trof
takes shape over the Great Lakes. 850 mb temps from the 12z GEFS
ensembles and ECMWF indicate a return to more normal temperatures
for the end of January as average 850 mb temps will range from -10
to -15 degrees C by the end of next week, which should translate
to highs in the mid 30s to around 40 Thursday, and from the upper
20s to lower 30s by next Friday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 637 PM CST Thu Jan 19 2017

IFR or lower condtions expected through the bulk of the 00Z TAF
valid time across the central Illinois terminals. Low
clouds/drizzle/fog will be widespread with a slow moving weather
system remaining in the vicinity. Winds will generally be light.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CST Friday for ILZ027>031-036>038-
040>044-047>054-061.

&&

$$

UPDATE...Bak
SHORT TERM...Geelhart
LONG TERM...Smith
AVIATION...Bak


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