Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 020938

Area Forecast Discussion
National Weather Service Lincoln IL
338 AM CST Fri Dec 2 2016

.SHORT TERM...(Today and tonight)
ISSUED AT 337 AM CST Fri Dec 2 2016

On the surface, cyclonic flow will continue through today, and this
will result in cloudy skies continuing over most of the CWA; except
for the south and southeast where skies will likely be or become
partly to mostly sunny this morning. The mostly cloudy skies,
combined with west to northwest winds, will cause temp advection to
be neutral, so temps will only rise into the lower to middle
40s...with the warmest temps being where the sunshine is.

Flow remains the same into the night as high pressure trys to build
into the region during the early evening hours. Winds will decrease
as well and models suggest skies could become partly cloudy during
the overnight hours. This will allow some radiational cooling to
occur, resulting in temps falling to below 30 degrees by early
tomorrow morning. High clouds will also begin to move into the area
from the southwest late tonight, but do not think this will prevent
temps from cooling overnight.


.LONG TERM...(Saturday through Thursday)
ISSUED AT 337 AM CST Fri Dec 2 2016

Strong 526 dm 500 mb low pressure over southern Quebec early this
morning with its upper level trof hanging back over the Great Lakes
region, will track into Maine and the eastern Canadian Marinetimes
by this evening, and off the Canadian east coast by Saturday morning
as weak upper level ridging nudges into IL and surface high pressure
noses into IL and the Ohio valley. This will provide dry and
seasonably cool weather to the region on Saturday with lighter
winds. A Mostly cloudy day over on Saturday though may be more peaks
of sunshine Saturday morning before mid/high clouds increase ahead
of approaching wx system. Highs Sat in the upper 30s from I-74
northeast and lower 40s southwest.

A more active weather pattern then returns to central and southeast
IL during the early and middle part of next week, with a blast of
colder Canadian air arriving during the 2nd half of next week. Three
weather systems to impact the area, and wintery mix of precipitation
possible with each one, especially the 1st and 3rd systems.

A northern stream short wave trof moves into the Midwest by Sunday
morning while a 558 dm 500 mb low moves into nw Mexico. These two
systems are not phasing initially and deeper southern moisture to
stay south of CWA overnight Sat night and Sunday. Lighter qpf around
a tenth inch expected over CWA with a bit higher amounts northern
CWA. Surface high pressure should continue to keep CWA dry through
Sat evening, then increasing isentropic lift and moisture to bring
in chances of light snow, possibly mixed with light rain sw CWA
overnight Sat night. Light snow likely early sunday morning, then
changes to light rain chances from sw to ne during mid/late Sunday
morning, so all light rain Sunday afternoon. Rain chances to be
diminishing quickly during mid/late Sunday afternoon. Snowfall
amounts of a half to 1 inch possible on grassy surfaces north of
I- 72 late Sat night into mid morning Sunday, with less than a
half inch south of I-72, little or no snow accumulations along and
south of I-70. Lows Sat night in the lower 30s. Highs Sunday in
the upper 30s to near 40F from I-74 northeast, and lower 40s sw of

Dry weather expected Sunday night and Monday across area with high
pressure moving over the Ohio river valley. Some sunshine possible
Monday morning (partly sunny), but will be clouding up during Monday
afternoon and 2nd stronger wx system approaches. Highs Monday in the
low to mid 40s. The cutoff upper level low over nw Mexico Sunday to
eject ne into west TN by dawn Tue and to mainly spread rain ne
across CWA during Monday night and Tue morning. NW CWA could be cool
enough to support light snow chances too overnight Monday night and
Tue morning, but little or no accumulations expected as coolest
temps in the mid to upper 30s early Tue morning. Highs Tue in the
lower 40s central IL and 45-50F in southeast IL. 00Z models have
trended quicker exiting 2nd wx system with dry conditions by Tue
afternoon and just slight chance of light precipitation Tue night.
Models have trended quicker bringing in colder air later Tue night
into Wed. Lows Tue night in upper 20s to near 30F over IL river
valley, and mid 30s in southeast IL.

Still differences with extended models handling 3rd wx system, but
most models agree with much colder weather arriving later Wed into
Thursday as strong upper level trof digs into the Midwest. Have
chances of rain/snow west of I-57 Wed afternoon. Highs Wed in mid
30s over IL river valley and lower 40s in southeast IL. Surface low
pressure to eject ne across the mid MS river valley and into the
eastern Great Lakes Wed/Thu though models not agreeing on timing and
position. Have chances of snow Wed night, with mix of rain/snow in
eastern IL Wed evening, then chances of few light snow showers or
flurries Thu/Fri in much colder air mass. Highs Thu and Fri in the
mid to upper 20s central IL and 30-32F southeast of I-70, which will
be the coldest days so far this season. Lows Thu night in the teens
over central IL with areas southeast of I-70 around 20F.


.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.




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