Area Forecast Discussion
Issued by NWS Central Illinois

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835
FXUS63 KILX 120534
AFDILX

AREA FORECAST DISCUSSION
National Weather Service Lincoln IL
1134 PM CST THU FEB 11 2016

.UPDATE...
ISSUED AT 908 PM CST THU FEB 11 2016

Light snow is just now beginning to move into western parts of
central Illinois, even though radar indicates it should already
be occurring. Observations show very few lower clouds so if any
light snow is occurring out there, it is flurries and the
observational sites are not picking it up yet. Still thinking that
some light snow will occur in the southwestern parts of the CWA
overnight, so believe current forecast still looks good for the
remainder of the night. May make some tweaks to overnight low
temps in the southeast, but remainder of the area, current
forecast looks fine. Update out shortly.

&&

.SHORT TERM...(Tonight)
ISSUED AT 323 PM CST THU FEB 11 2016

A fast moving clipper will produce light snow starting this evening
across western Illinois, with most of the focused lift overnight
primarily remaining across our southwestern counties. The general
trend in the 12z models has been to focus the better chances of
measurable snowfall over our southwestern and southern counties.
Have increased PoPs to likely in a narrow corridor southwest of a
line from Jacksonville to Effingham, progressing from SW to SE with
time overnight. The HRRR is the farthest southwest with the latest
updated path of forcing for precip, with the NAM80, Canadian GEM,
and ECMWF still extending at least some snow accumulation across all
of our CWA except the far NE counties NE of CMI. The NAM12 is
similar to the HRRR in limiting snow to the SW half of our CWA. Have
reduced the PoPs in our N and NE counties, north of I-74, to slight
chance. Chance PoPs were limited to generally south of a line from
Galesburg to Lincoln to Paris. Snow amounts from Jacksonville to
Effingham could reach between a half inch and one inch, with a
dusting to a half inch as far north as Rushville to Lincoln to
Decatur. South to southwest winds should remain less than 10 mph
during the snowfall, so drifting should not be a big problem
overnight.

Low temps tonight will generally settle out in the mid-teens, as
cloud cover limits the diurnal swing to only around a 10 degree drop-
off.

.LONG TERM...(Friday through Thursday)
ISSUED AT 323 PM CST THU FEB 11 2016

Friday may start out with a few lingering snow showers south of
I-70, but little additional accumulation is expected after
sunrise. The bigger story will be the arrival of very cold air on
increasing northwest winds Friday afternoon, as strong pressure
rises develop ahead of the surface high center. The tight pressure
gradient will produce wind gusts over 30 mph at times, which could
cause minor drifting of the snowfall from tonight, so slippery
travel could develop from that Friday afternoon and evening.

Wind chills late Friday night will drop very close to advisory
levels of -15F north of Peoria, with wind chills below zero in all
of our forecast area. Actual air temps will be range from zero to 8
above zero, but NW winds will remain strong enough to push wind
chills well below zero.

The next main concern will be the system for Sunday into Monday.
Model differences remain with the 12z model updates. The Canadian
GEM has started showing the splitting of energy as the trough
reaches Illinois, similar to what the ECMWF was showing yesterday.
The ECMWF has changed and now maintains the trough energy across
Illinois Sunday evening, with total QPF amounts that support snow
amounts of 1 to 2". The Canadian GEM QPF amounts support around 1
inch west of I-55, with little to no snow accum east of I-55. The
GFS remains the only model that develops a distinct surface
low/circulation that tracks across northern IL Sunday evening, with
total QPF amounts that support snowfall of 4" to 7" in our northern
counties, and 3-4" in the south. The 12z NAM now includes forecast
info through 6 pm Sunday, and is showing plenty of snow as well,
despite no surface low moving across IL. The NAM has 3-5" across our
counties for just the first 12 hours of the event through 6 pm
Sunday. We have increased PoPs into the likely category for Sunday
nearly everywhere, and likely PoPs east of I-57 Sunday night.

Our compromise forecast for QPF came out to 0.23-0.30", correlating
to snowfall amounts of 2-4", with the higher totals from Peoria and
north. There still remains quite a bit of uncertainty with how much
moisture will fall, so updates to QPF and resultant snow accums are
likely with subsequent model runs.

The accumulating snows should primarily be done by Monday morning,
but lingering light snow or flurries could continue into afternoon.
If precip does linger into the afternoon, the snow may mix
with or change to rain.

All of the extended models show a low deepening south of Illinois on
Monday, and progressing up into the Appalachian mountains Monday
night, with precip mainly southeast of our area. However, the
blended initialization kept slight chance PoPs in the eastern half
of Illinois Monday night through Tuesday night, mainly due to that
strong system.

A warming trend is indicated for next week, as upper level ridging
gradually pushes east into Illinois. We should see mid-level warming
increase enough to support high temps climbing into the upper 30s to
low 40s Tuesday and Wed, with sunshine and mid 40s to around 50 for
Thursday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 1134 PM CST THU FEB 11 2016

Snow has not begun at any of the TAF sites yet, but with mosaic
radar loop showing most of the snow still west of the area and
nothing being reported under the higher returns on radar, thinking
is that flurries will occur at most of the TAF sites overnight,
with SPI only site getting light snow overnight for a few hours
from 07z to 09z. Vis at SPI during the light snow will be 3sm
while remainder of the time, think vis will be VFR. Do not see
cigs dropping to MVFR levels until after the snow has ended over
the area, due to very dry lower layers...seen on 00z UA sounding
and any snow currently falling is just moistening up the lower
layer. MVFR cigs at 2.5kft will occur from early morning til
afternoon in the west and later afternoon in the east. Then clouds
will scatter out and last til evening. Winds will be light out of
the southwest to start, but then become westerly and then
northwesterly for the afternoon and evening. Light wind speeds til
after winds shift to west and northwest. Then speeds increase and
become gusty with gusts of 23-38kts possible.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...Auten
SHORT TERM...Shimon
LONG TERM...Shimon
AVIATION...Auten



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