Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 240359

Area Forecast Discussion
National Weather Service Lincoln IL
1059 PM CDT Mon Oct 23 2017

Issued at 842 PM CDT Mon Oct 23 2017

The initial cold front that was accompanied by a band of showers
was shifting into east central Illinois taking the rain with it.
A secondary cold front was analyzed now entering extreme west
central Illinois with widely scattered showers developing along
it as well. This second front will switch the winds into the
northwest and be rather gusty overnight and especially during
the day on Tuesday. Seeing 25 to 30 mph gusts across central Iowa
in the area of strongest pressure rises this evening so we may see
a few of those as the front shifts to our east later this evening.

Short term forecast models indicate this first wave of rain over
eastern Illinois will shift away from the forecast area while the
widely scattered showers associated with the second front moves
across central Illinois over the next several hours. Then we may
see a lull in the precip before scattered showers drop south into
our area Tuesday morning and will be with us on and off during the
day accompanied by a chilly northwest wind as afternoon temperatures
struggle through the 40s over most of the area with any 50 degree
or warmer temperatures confined to far southeast Illinois.

The current ZFP has a decent handle on the evening trends with only
minor adjustments made to the temperatures and with POPs in the
east for the next few hours, but the overall changes made will not
warrant an evening ZFP update at this time.


.SHORT TERM...(This evening through Tuesday)
ISSUED AT 255 PM CDT Mon Oct 23 2017

Deformation zone precipitation looks to linger through the late
afternoon from near I-57 eastward due to the upper level trough over
IN, lifting northeastward. A much faster moving shortwave,
meanwhile, is approaching from the northwest, currently over IA,
with an associated surface cold front already near the Mississippi
River. Showers associated with this system will move rapidly into
central IL this evening as it moves into an area of richer moisture.
Precipitation amounts will be light overnight, generally around a
tenth of an inch or less. Following tonight`s shortwave and cold
front, a larger scale upper trough will set up over the area with
embedded disturbances keeping showery weather through Tuesday. After
reinforcing cool air behind tonight`s cold front, lows will dip into
the lower 40s tonight, followed by highs only reaching the upper 40s
in most of central IL Tuesday.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 255 PM CDT Mon Oct 23 2017

Tuesday night, a pocket of -2 C 850 mb temperatures associated with
the trough will move across central IL, producing surface
temperatures approaching the freezing mark. Currently, it looks as
if temperatures will remain just above freezing, with relatively dry
and breezy conditions preventing frost toward Wednesday morning,
however this will need to be watched as conditions are precariously
close to the first freeze of the season.

A shortwave ridge will provide for dry conditions, mostly clear
skies, and milder temperatures climbing well into the 50s (Wed) and
60s (Thu) with lows only reaching the upper 30s to mid 40s.

Good model agreement then presents itself for Friday into the
weekend as all models/ensembles carve out a deep trough roughly
centered over Illinois, with an average 850 mb temperature around -7
C Saturday. This will bring a strong chance for sub-freezing low
temperatures either Friday night, Saturday night, or both. For now,
kept temperatures just below freezing Friday night and Saturday
night although a harder freeze is possible Saturday night, depending
on exact timing of the system. Highs look to range from around the
mid 40s to low 50s over the weekend.  Although temperatures would be
cold enough for a snow shower at times over the weekend, current
chances for any precipitation over central IL are too low to outlook
any snow. A shortwave ridge looks to bring highs back up to the low
and mid 50s Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1052 PM CDT Mon Oct 23 2017

VFR conditions are expected through about 06z, then we will see
deteriorating cigs develop from north to south with mostly MVFR
conditions expected across the entire area by 10z with the lower
cigs holding through the day. Scattered showers and isoalted
thunderstorms were occurring over parts of central and eastern
Illinois ahead of a rather vigorous upper wave seen on the water
vapor loop this evening. At the surface, a cold front was analyzed
to our west and as that boundary pushes across the area
overnight, the cigs will gradually lower and winds will veer more
into the northwest. Speeds should average from 10 to 15 kts with a
few gusts up to 20 kts later tonight.

Additional shower activity should spread southeast into the area
during the early morning hours but coverage appears to be rather
limited at this time so will try to cover that with VCSH for now.
As a secondary trof rotates southeast over the area tomorrow,
better coverage of showers is expected along with northwest winds
of 15 to 20 kts with gusts of around 25 kts at times through the
afternoon before the gusts start to subside just after sunset.




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