Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 031709

Area Forecast Discussion
National Weather Service Lincoln IL
1109 AM CST Sat Dec 3 2016

Issued at 952 AM CST Sat Dec 3 2016

Some thin spots in the clouds have developed this morning as the
stratocumulus deck finally pulls out and is quickly replaced by
the cirrus. Radar mosaics showing precipitation advancing
northward across Arkansas as well as over Nebraska and Iowa, and
these areas will be converging on central Illinois after midnight.
High-resolution model guidance, as well as the new NAM model,
showing a slower arrival after midnight, as there is a decent dry
wedge between 4,000 and 11,000 feet that will be moistening from
the top down. Have made some timing adjustments to tonight`s PoP`s
as a result.


.SHORT TERM...(Today and tonight)
ISSUED AT 348 AM CST Sat Dec 3 2016

High pressure ridge across the area will move east to northeast
today while a weather system approaches from the west. Precip will
not arrive until after midnight and with temps decreasing during the
night, initial indications are that precip will be mainly snow
across the CWA. Only place in the CWA where there could be rain is
in the extreme southeast where there could be a mix or rain and
snow. Pops will increase to likely toward morning in the west and
then be categorical northwest of the IL river. Despite the warm
ground temps, some accumulation of the snow will be possible, with
near one half inch possible northwest of the Illinois river and less
than that to the east and southeast.

.LONG TERM...(Sunday through Friday)
ISSUED AT 348 AM CST Sat Dec 3 2016

A busy forecast overall with several waves bringing precip through
the region with differing thermal profiles as the airmass changes in
the progressive pattern.  It seems the trend of the second and third
system to shift further south is continuing.

Saturday nights system will continue with the snow over the northern
half of the state through Sunday morning.  Warm air advecting in
from the S will help to transition the snow over to all rain from
south to north from mid morning through to sunset before the precip
comes to an end.  That same warm air will keep highs on Mon and Tues
in the low 40s in Central Illinois. A big surge of colder Arctic air
is making its way south and into the Northern Plains by midweek. By
Wednesday, most areas north of Interstate 70 have high temperatures
below freezing...everywhere on Thursday.

Back to the precipitation, however, the second system is making its
way up from the SW into the region for Monday night/Tuesday.  The
better chances for precip are in the south...with a transition to
rain/snow mix the further north into the cold air.  00Z model runs
are a little quicker with the progression of the system, leaving
Tuesday afternoon mostly dry, eliminating some of the westward
extent to the NWrn quadrant of the surface low.  Suspect the low
pops in the blend is an echo of prev solutions and should the trend
continue...pops may fall out in subsequent runs for Tuesday evening.
Pops creep back in with a quick open wave rippling through the
midsection of the country with another shot of snow Wed
afternoon/evening and overnight.  Major timing differences between
the GFS and ECMWF still at this point, varying by about 6-12 hrs.
Expecting changes to the timing of that precip.  Cold temps settling
in to wrap up the week with lows dipping into the teens by Thursday


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1109 AM CST Sat Dec 3 2016

Main forecast concern is development of MVFR and potential IFR
conditions after about 09Z as snow spreads into central Illinois.
Ceilings will steadily decrease and will be close to 1000 feet by
12-15Z. Large flakes of snow will result in visibility going down
quite a bit, with some improvement late in the period as the
precipitation begins to mix with rain.




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