Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 020522
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1122 PM CST Thu Dec 1 2016

.UPDATE...
Issued at 858 PM CST Thu Dec 1 2016

Low clouds covering central IL continue to stream across the area
in WNW flow although the southern edge has dissipated somewhat
with partial clearing into southeast IL south of I-70. The
southern edges of the forecast area into areas south of I-70
should be the least cloudy overnight given the trajectory of the
cloud shield...so cooler temperatures reaching near the freezing
mark overnight look good in those areas...while most areas to the
north should see mid 30s. Winds west generally 5-10 mph through
the night. Only minimal updates for temperature and cloud trends
needed this evening.

&&

.SHORT TERM...(This evening through Friday)
ISSUED AT 255 PM CST Thu Dec 1 2016

Low clouds continue to blanket central and southeast Illinois early
this afternoon: however, latest visible satellite loops are showing
the southern edge of the cloud shield gradually dissipating. 20z/2pm
satellite indicates the clearing line extending from near
Kirksville, Missouri to Salem, Illinois.  With only a couple more
hours of daylight left, do not think clearing will make it much
further north...so am expecting overcast conditions to prevail
across the entire KILX CWA through the remainder of the afternoon.
Most of the models are not handling the low-level moisture field
well at all, with 12z NAM and GFS forecast soundings suggesting
partial clearing across the area this afternoon.  Rapid Refresh
seems to have the best handle on the current situation, so have
followed its solution most closely in the short-term.  With ridge of
high pressure remaining W/SW of Illinois tonight then shifting
slowly eastward over the area on Friday, thermal advection will
remain weak and the low-level moisture will likely remain in place.
As a result, have continued with a cloudy forecast tonight into
Friday...with some partial clearing during the day Friday across the
far S/SE CWA.  Due to the extensive cloud cover, have decided to go
above guidance numbers for lows tonight, with readings staying in
the lower to middle 30s much like last night.  Have gone slightly
below guidance for highs on Friday, with lower to middle 40s common.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 255 PM CST Thu Dec 1 2016

An active weather pattern over the Midwest during this forecast
period with a transition to colder weather by later next week. Two
or possibly three weather systems, depending on which model you
prefer, to affect our area during the next week with the first of
these storm systems moving in towards dawn on Sunday. Soundings
continue to show top down saturation occurring in the 09z-12z time
frame with enough warm air at in the boundary layer for more of a
rain snow mix, especially across the north before it becomes all
rain during the day.

The upper wave should quickly move off to our east by Sunday evening
with our next shortwave ejecting out of the southwest U.S. on
Monday. The GFS is a bit flatter and further south with the track of
the upper wave compared with the ECMWF. This translates to a further
southeast track with the surface low but soundings continue to
suggest mostly rain with this system as well as temperatures warm
into the mid 40s Monday afternoon with overnight lows holding
mostly in the mid to upper 30s Monday night when the bulk of the
precip will occur.

The second shortwave will shift away from our area by late Tue/Tue
night with some significant model differences seen with any
additional waves tracking out of the mean longwave trof across the
southwest U.S. The current GFS suggests the system on Tuesday will
be the last one as the surface wave intensifies to our northeast by
evening drawing in the much colder air from the northwest by
Wednesday, while the ECMWF holds back the cold air intrusion
about 18-24 hours longer until one more shortwave and surface low
tracks across the area Wednesday night and Thursday. Feel the GFS
is too progressive in the highly amplified pattern next week with
a solution more in line with the slower ECMWF looking more
reasonable at this time. Based on the slower forecast, rain will
overspread our area again Wednesday afternoon and night and then
transition over to light snow on Thursday as the much colder air
sweeps in as the deep surface low shifts off to our northeast.
Highs by the end of next week will struggle to get out of the 20s
with early morning lows in the teens to lower 20s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1122 PM CST Thu Dec 1 2016

MVFR cigs to continue over portions of central IL for the next 24
hours. A steady stream of low clouds in WNW flow looks to be
predominant over the next 24 hours although the southern boundary
of the cloud shield will be close to KSPI-KDEC at times and may
result in VFR conditions spreading northward over those sites.
Best chances for VFR conditions will be at KSPI which already has
cigs above 3000 feet and upstream observations also above 3000
feet. Have therefore kept forecast VFR at KSPI through the
period...but other sites have been kept MVFR through at least 16Z.
Winds W 6-12 kts through the period.

&&

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

&&

$$

UPDATE...Onton
SHORT TERM...Barnes
LONG TERM...Smith
AVIATION...Onton


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