Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 031139

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

.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 12Z TAFS through 12Z Sunday morning)
Issued at 539 AM CST Sat Dec 3 2016

High pressure will continue to dominate the weather at all TAF
sites this morning and into this afternoon. Lower VFR clouds
present at all sites and model RH forecasts and satellite trends
show clouds pushing up to the northeast through the morning. So
believe these clouds will finally go away, but mid clouds around
12-15kft will blanket the TAF sites this afternoon and into early
this evening. The next weather system approaching the area tonight
and could bring precip to the TAF sites late tonight. Models
differ on timing of the precip, so will not get too aggressive with
onset of precip. Believe any reduction in vis and lowering of cig
heights into MVFR ranges will hold off til after end of TAF
period. Think some light precip will be possible after around 09z
at all sites except CMI. P-type could be mix of rain and snow, but
will just go all snow at this time. Winds will be light and
variable through most of the forecast period due to the high
pressure ridge dominating the weather in the area. Then after the
high pressure shifts east, winds will become southeasterly, though
speeds will remain less than 10kts.




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