FXUS63 KILX 170939

Area Forecast Discussion
National Weather Service Lincoln IL
339 AM CST Sat Nov 17 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 339 AM CST Sat Nov 17 2018

Main concerns in the short term will be the shortwave pushing
across northern Illinois today, with a surface boundary stalling
out across central IL tonight. Primary focus remained on the
resultant precipitation type and amounts through tonight. Radar
and satellite are depicting an area of precipitation edging
southward into our northern counties. The precip appears to be
associated with some low-level frontogenesis occurring along a
baroclinic zone. Initially there will be some low level dry air to
overcome before precip reaches the ground, as evidenced by cloud
ceilings at 10K ft in our N counties, where radar returns show
some precip potential. High resolution guidance continue to
indicate the main forcing for precip will remain just north of our
counties. However, the GFS, NAM, and ECMWF all show a farther
southward push to the baroclinic zone today. Overall trends in the
satellite and radar so far point toward a more zonal (East-West)
push this morning, which should lend more confidence in the high
res models solution keeping precip mainly north of Peoria to

Model soundings confirm the dry layer between 900mb and 750mb at
12z, then saturating by 15z. As clouds are developing ahead of
precipitation, surface temps are rising to around or just above
freezing, with upstream reports of rain overnight on the southern
flank of the precip shield. With wetbulb temps (Tw) below
freezing through nearly the entire column, we should see only a
brief shot at freezing rain to start, then precip change to snow
as evaporative cooling drops temps aloft below freezing to the Tw.

There is evidence in all models that the shortwave will weaken
with time today, leaving spotty snow showers changing to rain
showers this afternoon. We expect little to no snow accum with
this mornings wave, and even minor rain totals for the afternoon.

A secondary push of energy is projected for tonight, as a surface
low passes by to the south of Illinois. An inverted trough
extending northward from the low into the cold air will help to
energize the baroclinic zone tonight, producing a west-east band
of snowfall starting in our N counties, then shifting southward as
it rotates slightly counter-clockwise. There appears to be enough
moisture available to the system and lift generated tonight to
produce a quick shot of 0.5" to 1" of snow, mainly north of I-72.
There remains low potential that later tonight the precip could
transition to freezing rain between I-72 and I-70, but think the
models are overdoing the warm layer aloft and will keep primarily
snow in that zone.


.LONG TERM...(Sunday through Friday)
ISSUED AT 339 AM CST Sat Nov 17 2018

The forcing for precip will weaken on Sunday morning, as the band
of snow rotates and shifts eastward. There will also be a
transition from snow to rain with time as the precip diminishes
into Sunday afternoon. Spotty rain showers could linger Sunday
afternoon south of I-70, however, little to no QPF is expected
after noon. Yet another wave of energy Sunday night will progress
along the boundary across our southeast counties. An area of rain
changing to snow is forecast for areas south of Shelbyville to
Paris. Little to no snow accum is expected during that phase of
the system, then dry conditions are expected through Thanksgiving
night. A period of rain showers are advertised in the extended
models for Friday and Friday night.

As for temperatures, relatively cold conditions will continue
through Tuesday night, then a warming trend will highlight the
rest of the week. High temps on Thanksgiving should range from the
upper 40s toward Galesburg and Peoria, to the lower 50s south of
I-70. Slightly warmer temperatures are projected for Friday and
Saturday, as southerly breezes prevail.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1136 PM CST Fri Nov 16 2018

Still some lingering ceilings around 1200 feet near KCMI as of
05Z, which may be difficult to erode with high clouds streaming
above the cloud deck. Ceilings expected to deteriorate from north
to south late tonight, with patches of fog reducing visibility as
well. Will largely go with IFR conditions from late tonight
through the balance of the forecast period. Main concern for any
precipitation looks to begin around 15Z near KPIA/KBMI, then after
18Z further south.




LONG TERM...Shimon
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