Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 090244

Area Forecast Discussion
National Weather Service Lincoln IL
844 PM CST Thu Dec 8 2016

Issued at 840 PM CST Thu Dec 8 2016

A weak surface trof noted on the latest analysis this evening
over east central Iowa has been producing scattered flurries
across the forecast area, especially over the north and east.
We expect this activity to continue until the trof axis shifts
off to our east by Friday morning. Will extend the scattered
flurries into the early morning hours and may have to edge the
chances a bit further south as well. Lower cloud deck is now
starting to shift more to the south than what we saw earlier in
the day so it appears all of our forecast area will be drapped in
the clouds by late tonight. We did have some brief clearing from
Springfield west to Jacksonville over the past few hours, but
that is about to end as the lower clouds settle back to the south
this evening. The updated ZFP should be out by 900 pm.


.SHORT TERM...(This evening through Friday)
ISSUED AT 240 PM CST Thu Dec 8 2016

1045mb high extending from Alberta/Saskatchewan southeastward to
Oklahoma will shift slowly eastward over the next 24 hours...with
the ridge axis eventually reaching the Mississippi River by Friday
evening.  In the meantime...central Illinois will continue to be
influenced by cyclonic flow around a deep upper low over Quebec.
Widespread cloud cover currently blankets central/northern
Illinois...with the southern edge of the cloud shield roughly along
a Des Moines, Flora line.  Main short-
term challenge will be predicting how quickly the clouds shift
eastward.  With deep-layer northwesterly flow in place, any
appreciable clearing will be slow to take place.  While model
solutions vary, think slow is the way to go in this particular
pattern.  As a result, will continue with a mostly cloudy forecast
across much of the CWA tonight and Friday.  Skies will at least
partially clear along the S/SW periphery of the CWA...especially
along/southwest of a Robinson line.
A few snow flurries have been reported from time to time beneath the
overcast, so have included mention of flurries across the northern
CWA through tonight.  Due to persistent cloud cover and northwest
winds, much below normal temperatures will continue...with lows
tonight in the teens and highs on Friday remaining in the 20s.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 240 PM CST Thu Dec 8 2016

Temperatures will begin to moderate to start the period. These
milder, but still below normal, temperatures will last through the
beginning of next week before the next shot of Arctic air arrives.

The precipitation scenario for the weekend has changed a bit since
yesterday, and model agreement is better. A clipper type wave will
streak across the area Saturday afternoon and night bringing a quick
shot of snow to northern portions of the forecast area. This wave
has trended further north the last few model runs, and would expect
most of the snowfall to occur along/north of the I-74 corridor.

A more substantial wave will dig into the Plains on Sunday,
developing a surface low that will track northeast across the
forecast area Sunday night. This system looks increasingly like it
will tap into enough warm air that the precipitation on the warm
side of the low will mostly fall as rain, while mostly snow is
expected on the cold side. This is resulting in a complicated
weather type forecast across the forecast area from Sunday afternoon
through Sunday night, as there are still important differences in
the forecast storm track. A blended solution remains the way to go
given the uncertainty, and expect several forecast adjustments to be
needed to the details between now and Sunday. At this point, the
window for all snow, with sufficient intensity, looks too small for
significant snow accumulation.

Quiet weather returns for Monday. The passage of an Arctic cold
front Tuesday/Tuesday night will be accompanied by snow showers, but
they should not be significant. However, the cold air behind the
front will be (significant).


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 512 PM CST Thu Dec 8 2016

Backedge of low VFR/MVFR clouds extend from KFSW to just south of
K3LF with some erosion noted over extreme western IL over the past
few hours. Overall, this band of clouds was tracking southeast
with a slight eastward shift seen in the latest satellite data.
However, with northwesterly flow locked in place across the region
any eastward shift in the cloud cover will be on the slow side.
KSPI the closest to the clearing this evening and will keep an eye
on the clearing just to its west and make a last minute call on
that site. Further north and east, MVFR clouds should hold thru
the night before we see cloud heights come up to low VFR excpt for
KBMI where MVFR cigs are expected to hold. Surface winds will
diminish out of the northwest to 7 to 12 kts and then turn more
into a west to northwest direction on Friday with speeds ranging
from 8 to 13 kts.




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