Area Forecast Discussion
Issued by NWS Central Illinois

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321
FXUS63 KILX 210542
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1142 PM CST Fri Jan 20 2017

.UPDATE...
Issued at 844 PM CST Fri Jan 20 2017

Tricky overnight cloud forecast, which will have an impact on
additional fog potential. Satellite loops had clearing surging
toward the area from Missouri earlier this evening, and last
several runs of the HRRR suggesting this clearing would quickly
spread across the forecast area. However, more recent satellite
loops has shown low clouds redeveloping back toward Missouri. A
warm front still lies across northern portions of the forecast
area, with more significant low clouds/fog/drizzle along and to
the north of this boundary. Still expect this boundary to push
north of the area by morning, and drier low-level air to the south
of the boundary should allow the upstream clearing to gradually
make its way north. Have updated forecast to be a little more
optimistic with sky condtions overnight. Otherwise only minor
hourly tweaks were needed.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 245 PM CST Fri Jan 20 2017

Warm front continues to take shape near the I-72 corridor this
afternoon. Temperatures closing in on 60 degrees over the far
southeast CWA this afternoon with mid-upper 40s north of the
boundary. Some of the fog has redeveloped near the boundary,
although visibilities mainly in the 2-4 mile range.

The inversion around 850 mb will continue to hang on for the first
part of the evening, before finally breaking down as the front lifts
further north. Short range models continue to hint at some
development by late afternoon, lifting northward with the front this
evening. With very dry air above the inversion, thinking that any
precipitation will be in the form of drizzle, and have continued
with the associated low PoP`s this evening, although diminishing
from south to north with time. Have maintained a mention of fog in
the forecast, but this would become less of a threat with time as
the front lifts north. Temperatures not expected to change too much
tonight, ranging from the mid 40s near Galesburg, to the lower 50s
from about I-72 southward.

Nice southerly flow will bring 850 mb temperatures into the 8-9C
range on Saturday. With the soundings suggesting partly sunny
conditions developing, it looks like the majority of the CWA should
reach into the 60s for highs, with upper 50s across the north. This
would be close to records in a few areas (see climate section
below).

.LONG TERM...(Saturday night through Friday)
ISSUED AT 245 PM CST Fri Jan 20 2017

After an unseasonably warm day on Saturday, models continue to
indicate a weak cool front will push across the area Saturday night
into Sunday morning. Rather steep lapse rates on soundings from 800-
500 mb with Most Unstable Cape values ranging from 700 to 900 J/KG
late tomorrow afternoon and night. It appears as a southern stream
shortwave and surface low track well to our south later Saturday
evening into Sunday morning, a large complex of showers and
thunderstorms will develop over the lower Mississippi Valley which
may effectively hold back any deep moisture transport north into
our area along the slow moving boundary. Will continue to carry
low chance POPs Saturday with the highest chances east of
Interstate 55. Another warm night for January with Sunday morning
lows forecast to be some 5 to 10 degrees above normal highs for
the middle of January with readings ranging from the middle 30s
northwest to close to 50 in far southeast Illinois.

The stronger southern stream system will continue to stay well south
of our area on Sunday keeping the heavy rains and thunderstorms
away from the forecast area. Low chance POPs will be along and east
of the I-57 corridor than translating into southeast Illinois by
afternoon as the surface low tracks further away from the Midwest.
Although not as warm as Saturday, Sunday`s highs will once again
be well above normal with readings in the upper 40s northwest to
around 60 over far southeast Illinois. As the deep upper and surface
lows slowly track north up the East Coast early next week, weak upper
level ridging will build over the Midwest bringing quiet weather to
start the new work week off with. Will still have the threat for
some lingering light rain over far east central and southeast
Illinois Monday morning, but for the most part, the bulk of any
significant rainfall early next week will be well of to our east and
southeast. Another day with above normal temperatures as highs top
out in the low to mid 40s.

Due to the slow movement of the upper low to our east and shortwave
ridging across our area early next week, models have trended a bit
slower with our next chance for precip as another storm system
develops across the Central Plains on Tuesday. We will still have
low chance POPs over our far west and northwest counties by late
Tuesday afternoon, but it appears any rainfall with this system
will hold off until Tuesday night into Wednesday with our north
having the higher chances during this time frame. A fairly decent
warm axis seen just ahead of the storm system Tuesday afternoon
may help to push temperatures well into the 40s with 50s not that
far to our south. Once the storm system tracks to our north on
Wednesday, we should start to see a gradual cooling trend set in for
the latter half of the week with temperatures returning closer to
where they should be for late January.

Medium range models today not showing much agreement with respect to
how deep the trof strengthens over the Great Lakes with the latest
ECMWF backing off considerably from what we saw 24 hours ago, while
the 12z GFS continues to indicate a rather deep trof over the lower
Great Lakes by the end of the month resulting in below normal temps,
a solution currently supported by the 12Z GEFS ensembles. Current
forecasts suggest temperatures by the end of this forecast period
will return to more normal levels. At this point, we are not seeing
any solid model consensus of any significant upstream blocking or
buckling of the Polar jet, which would allow more of a cross polar
flow to develop, which would bring some of that very cold air
currently bottled up in northwest Canada and Alaska southward
with 850 temps ranging from -25 to -30C this morning.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1137 PM CST Fri Jan 20 2017

A warm front has lifted most of the way north of the central
Illinois terminals this evening. This has helped conditions to
improve to MVFR or VFR. As skies try to clear overnight,
additional fog development is possible, but widespread heavier fog
is not anticipated. Southerly winds increase Saturday to the south
of the front, becoming gusty at times. Clouds will thicken up
again late tomorrow afternoon/evening as a weather disturbance
pushes into the area.

&&

.CLIMATE...
Issued at 245 PM CST Fri Jan 20 2017

Record highs for Saturday:

Bloomington............ 62 (1906)
Champaign.............. 62 (1906)
Decatur................ 69 (1906)
Galesburg.............. 66 (1957)
Lincoln................ 60 (1964)
Olney.................. 68 (1986)
Peoria................. 62 (1957)
Springfield............ 63 (1986)

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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



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