Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 062111
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
311 PM CST Tue Dec 6 2016

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 311 PM CST Tue Dec 6 2016

High pressure ridging will build into the area tonight and
Wednesday. Clearing line will make its way across the remainder of
the forecast area this evening in the wake of a cold front pushing
through the Midwest. Plume of mid-level moisture over Oklahoma will
push northeast into the area late tonight and Wednesday.  The
combination of the incoming cloudiness, dry air advecting in with
the ridge, and winds remaining up around 5 kts should reduce the
potential for fog tonight and keep temps mostly in the 20s overnight.

Mostly Cloudy skies and continued cold advection will keep high
temps on Wednesday below normal for early December. Latest models
have backed off on producing any light precip for Wednesday
afternoon and have removed slight chc pops that had been in earlier
forecast packages.

&&

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 311 PM CST Tue Dec 6 2016

The models have all come into agreement that the Wednesday night
system will no longer affect central Illinois in terms of
precipitation. The surface ridge axis is now expected to prevail
over what portion of the 500mb shortwave that moves across Illinois
Wed night.

With the 12z model updates, it appears we may end up seeing some
virga develop on Thursday as the upper trough axis progresses across
Illinois. Any precip that reaches the ground should remain to the
north of our forecast area. In any event, clouds will increase on
Thursday as a result of the trough passage.

The bigger story for Wed night and Thursday will be the arrival of a
significantly colder air mass. Steady NW winds later Wed night will
contribute to wind chill readings in the zero to 5F range N of I-74,
as low temps bottom out in the mid teens. Lows for areas south of I-
70 will drop into the low 20s with wind chills around 10F by 12z/6am
Thurs. That cold dry air will remain the main influence on our
weather through Friday night, with daytime highs in the 20s and
overnight lows in the teens. Wind chills Friday morning will be
range from around zero towards Galesburg to around 8F near
Lawrenceville.

There appears to be some better agreement for the weekend system in
terms of precipitation timing. Differences remain in the surface
pressure pattern. The Canadian and GFS develop a closed low at the
surface Saturday night west of Illinois and progress it across NW
Illinois into the Great Lakes by late Sunday afternoon. The ECMWF
keeps more of an open wave of low pressure with a frontal passage
across Illinois in the same general time frame. The resultant
weather is generally the same, with precipitation developing in
central Illinois Saturday night and continuing through Sunday
afternoon. The precip type looks to start out as snow, then a surge
of warm air on Sunday could progressively change snow to rain as far
north as I-74 Sunday afternoon. Snowfall amounts this far out are
very difficult to pinpoint, but an inch or two would not be out of
the question based on current model trends. The strength and path of
any surface low will play the major role in how that scenario plays
out.

One major model difference occurs Sunday night as the ECMWF develops
a secondary low to the southeast of IL and moves it northeast into
Ohio by Monday morning. During that time, an additional wave of snow
is spread across central and southern Illinois Sunday night into
Monday morning. For now, we only left slight chance PoPs for snow
during that time frame, due to two opposing dry model solutions.
High pressure should provide dry conditions on Tuesday, but clouds
look to remain in place.

A warming trend is indicated for later this weekend and early next
week, as warm air surges north ahead of any low pressure system. So
high temps should return to the middle to upper 30s Sunday, with
slightly cooler highs on Monday and Tuesday but still all of our area
in the 30s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1113 AM CST Tue Dec 6 2016

Precipitation has exited the forecast area but MVFR vsbys remain
at I-72 terminals with IFR at KBMI. Vsbys should continue to
improve however stratus will likely remain in place through early
this afternoon. Clearing line crossing the Mississippi will push
east moving through the central Illinois this afternoon.

Models suggest mid-level clouds will overspread the surface ridge
in place over Illinois late tonight and early Wednesday associated
with a plume of moisture over the southern plains. Attm it appears
that CIGS should remain VFR. The combination of the incoming
clouds and 5-10 kt winds overnight should reduce the potential for
BR compared to this morning.


&&

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

$$

SHORT TERM...Barker
LONG TERM...Shimon
AVIATION...Barker



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