Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 091800
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1200 PM CST Fri Dec 9 2016

.UPDATE...
Issued at 956 AM CST Fri Dec 9 2016

1515z/915am visible satellite imagery shows a large tear in the
prevailing overcast developing along a Galesburg...to Clinton...to
Paris line. This feature has been expanding over the last couple
of hours, resulting in partial clearing along and near the I-74
corridor. Further north and south, cloudy skies and scattered snow
flurries persist. Models have been handling the low-level moisture
field quite poorly today, so will need to keep an eye on the
clearing and see exactly how far it expands. Most solutions
suggest any holes in the overcast will eventually fill back in
this afternoon, resulting in a partly to mostly cloudy day across
the board. Have also been watching a patch of heavier snow-showers
dropping southeastward across Macon/Christian counties. Visbys
were briefly reduced to 2 miles at the Decatur Airport as they
moved through, so would not be surprised to see perhaps a dusting
of snow on grassy surfaces across this area. Elsewhere am only
expecting a few flurries from time to time. Afternoon highs will
once again be below normal for this time of year, with readings
remaining in the middle to upper 20s.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 310 AM CST Fri Dec 9 2016

Satellite loops and upper air data display northwest flow aloft over
midwest, with the upper trof drifting to the east. Upper trof
continues to provide enough support to trigger flurries over
area, that should last into the mid morning hours, when trof moves
through and weak high pressure builds in. Expect low clouds to
lift and move to the east with drier air in low levels through
morning. However in the afternoon upper level clouds ahead of the
next system will fill area in so mostly cloudy conditions will be
rule.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 310 AM CST Fri Dec 9 2016

Not much has changed in the forecast this morning. Cold temperatures
and a few rounds of precipitation...with this weekend being more wet
and cloudy than anything else...some snow, some rain, some wintry
mix, and some melting. After the precip moves through, another deep
wave makes its way into the CONUS, bringing a lot of bitterly cold
Arctic air into the Midwest for next week.

Northwesterly flow over the country is starting to modify with the
wave off the Pacific NW coast...going more zonal into the weekend.
As the surface high slides east, winds become more southerly,
setting up a warm air advection regime ahead of the next precip
chances.  A quick wave moving through the zonal flow makes its way
into IL for later Saturday, bringing a quick round of snow,
particularly to the northern third of the state.  Some light
accumulations may be possible mainly along and north of I-74 through
Saturday night.  The bigger wave accompanies a developing sfc low
moving out of the Southern Plains for Sunday.  Precip chances carry
over and increase into Sunday afternoon/evening as the best dynamics
move into place in the Midwest.  The WAA regime set in place for
Saturday will bring more moisture for the precip...and the trend
will be to shift from snow on Sunday morning...to rain...from south
to north, throughout the day. The transition from snow to rain will
likely be accompanied by a wintry mix as the warm air pushes back
against the cold air in place over the region. That rainfall on
Sunday will erode the snow totals overall with the melting, as well
as create a sharp cut off between keeping snow on the ground/no snow
depth by late Sunday afternoon. Change over back to snow from NW to
SE as the night carries on and into the morning hours, resulting in
an inch or so of accumulation from Fulton Co over to Bloomington and
points north.  Keep in mind that with the sharp cut off with the
rain/snow likely to move...adjustments in the forecast will make the
difference between an inch or snow on the ground...and closer to 3
where the precip never changed over.  Much of Central Illinois may
light accumulations, but limited by rainfall.

Beyond the precip issues with the weekend...cold air is coming for
next week.  Highs by midweek already showing as teens and low 20s
for Wednesday through the end of the week, as a frigid Arctic
airmass moves into the CONUS. A major difference in the models in
handling a quick shortwave midweek, with the ECMWF in more amplified
flow pushing the precip further south than the GFS.  End result is
some low chance pops for now, with little confidence in timing or
placement.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1146 AM CST Fri Dec 9 2016

MVFR ceilings prevail across central Illinois late this morning
and are expected to persist through the afternoon. Forecast
soundings generally show the low clouds hanging around through
early evening, before ceilings climb into the VFR category from
mid-evening through Saturday morning. Winds will initially be
northwesterly at 10kt or less, then will become light/variable
tonight as high pressure moves overhead. A light S/SW wind will
develop on Saturday as the high shifts to the east.

&&

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

$$

UPDATE...Barnes
SHORT TERM...Goetsch
LONG TERM...HJS
AVIATION...Barnes


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