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Area forecast discussion
National Weather Service Lincoln Illinois
527 am CST Fri Dec 9 2016

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

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 northwest 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 Illinois 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 warm air advection regime set in place for
Saturday will bring more moisture for the precip...and the trend
will be to shift from snow on Sunday 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 northwest to
southeast 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 Continental U.S.. a major difference in the models in
handling a quick shortwave midweek, with the European model (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


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 524 am CST Fri Dec 9 2016

Infrared imagery still shows cloud deck over central Illinois with only little
movement through nightime hours. Has been some gradual slow
raising of ceilings, and so expect that to slowly continue, plus
with some drier air, will allow conditions in the afternoon to
improve to mid deck conditions. Good vsb expected.


Ilx watches/warnings/advisories...

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