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Area forecast discussion 
National Weather Service Lincoln Illinois
537 am CST Fri Dec 19 2014

Short term...(today)
issued at 459 am CST Friday Dec 19 2014

High pressure is expected to hold over central Illinois through
today with the next southern stream shortwave, currently over south
central Texas early this morning, forecast to track well south of
our area. 2am satellite data and surface observations showing an
area of clear skies extending from just northwest of Peoria
southeast thru Champaign and Decatur. Short range models suggest
this area will gradually fill back in with clouds as the day wears
on. Forecast soundings from the hrrr and rapid refresh models also
support this idea thru the day with the last few satellite frames
off the infrared loop indicating the clouds over far west central Illinois were
starting to shift more to the east. Forecast soundings across
central Illinois today support afternoon temperatures in the low to mid
30s with another day with very little wind, something that is a bit
on the rare side for December across our area.


Long term...(tonight through thursday)
issued at 459 am CST Friday Dec 19 2014

Main focus remains with active pattern setting up for the upcoming
Holiday week.

Powerful jet of 120-160 knots at 300 mb will be coming into the
Pacific northwest later this weekend before diving toward the
Southern Plains, helping to carve out a deep trough over the central
U.S. The GFS and European model (ecmwf) models are in good agreement with development
of a closed low over eastern South Dakota by midday Monday, with
some minor disagreements as to the amount of wobbling of this low as
it drifts toward the east. The European model (ecmwf) brings the center as far south
as Springfield by Wednesday morning, while the GFS and Canadian
models are centered across Wisconsin.

Precipitation shield with this system expected to start spreading
into the Illinois River valley by late Monday morning, then eastward
across the state during the day. The GFS is more prominent with a
dry slot punching in already by late evening, while the European model (ecmwf)
lingers the rain into Tuesday morning. Leaned more towards the
slower European model (ecmwf) solution and increased rain chances to around 60%
Monday night north of I-74 and east of I-57. Forecast soundings are
well above freezing up to around 850 mb, so have removed any mixed
precip wording for Monday night. Some mixture possible northwest of
the Illinois River on Tuesday, although a loss of ice crystals aloft
with the dry slot may mitigate this.

As we head toward Christmas eve, amount of wrap-around precipitation
is a concern. The European model (ecmwf) rapidly intensifies the surface cyclone to
our east, with central pressure down to around 978 mb midday near
Cleveland. This solution brings periodic snow showers southeast into
our area in the strong northwest flow. The much weaker GFS has some
flurries lingering through the day, with less windy conditions. Have
kept precipitation chances across the east during the day on the
edge of the ecmwf's dry slot, but kept only slight chances elsewhere
for now. Snowfall amounts still appear to be on the light side, but
Holiday travel will still not be pleasant with the snow and the
winds. Christmas day itself appears dry.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 525 am CST Friday Dec 19 2014

High pressure centered from northeast Iowa southeast thru central
Illinois has helped to scour out some of the MVFR clouds that
have dominated our area over the past 24 hours, especially along
the ridge axis early this morning. Satellite data indicates the
clear area extended from Moline southeast thru Peoria, Bloomington
and Champaign with MVFR cigs to the north and south. Forecast
soundings continue to suggest areas that were experiencing the
clear skies this morning should see the low VFR and even some MVFR
cigs move back in by later this morning into the afternoon hours.
Confidence on timing and extent of the lower VFR and MVFR cigs
across the area today is rather low, so will trend with more
clouds across the north and east by later this morning into the
afternoon hours but keep it mostly low VFR at this time. Surface
winds will once again be a non- factor today as our area will be
under the high pressure system so will continue with a light and
variable wind over most of the area into tonight.


Ilx watches/warnings/advisories...


Short term...Smith
long term...geelhart

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