Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 081803
AFDILX

AREA FORECAST DISCUSSION
National Weather Service Lincoln IL
1203 PM CST MON FEB 8 2016

.UPDATE...
ISSUED AT 1027 AM CST MON FEB 8 2016

Clouds and scattered snow showers blanket central Illinois this
morning...thanks to a deep upper-level low centered over southern
Lake Michigan. 16z/10am water vapor imagery shows a well-defined
vort max rotating around the parent low into northwest Illinois.
This particular feature is triggering a more concentrated area of
snow showers from eastern Iowa into west-central Illinois.
High-res models such as the HRRR/Rapid Refresh suggest this area
of snow showers will track E/SE across the KILX CWA through
mid-afternoon. Once the wave passes, synoptic subsidence in its
wake will likely lead to a lull in the precip late this
afternoon/evening before another weak feature approaches from the
north tonight. While visibilities will be reduced to between 1 and
3 miles at times within the snow showers, accumulations will
remain minor at generally less than one half an inch. With brisk
northwesterly winds bringing colder air into the region,
temperatures will continue to fall through the 20s for the balance
of the day. Current forecast has a good handle on the situation,
so other than a few minor tweaks, no major changes are anticipated
at this time.

&&

.SHORT TERM...(Today)
ISSUED AT 333 AM CST MON FEB 8 2016

Surface low centered over lake Superior early this morning has a
trailing cold front which has arrived in Galesburg early this
morning and will push southeastward to Lawrenceville by around noon.
An upper level shortwave following the cold front will help enhance
lift over the area bringing the likelihood of scattered snow showers
across central IL developing this morning through afternoon.
Forecast soundings depict a mixed layer deepening to the 800 mb
layer by afternoon...extending into temperatures aloft -10 C or
colder...for favorable snow crystal formation. Nevertheless...lift
is weak and only expecting amounts to around 1/2 inch or less by
evening. Early in the morning...a few sprinkles and showers
associated with a preceding shortwave will also be seen south of I-
72 before the more prominent shortwave and cold front arrive.

Cold air behind the front will start a downward trend in
temperatures. Most areas north of I-72 will see temperatures falling
through the day...while areas to the south should see a max
temperature before noon...then falling through the afternoon. Expect
early morning temperatures in the upper 20s and lower 30s...and no
more than mid 20s to lower 30s by mid afternoon. Winds WSW around 10
mph ahead of the cold front...switching to WNW and increasing to a
blustery 15-20 mph with gusts 25-30 mph.

.LONG TERM...(Tonight through Sunday)
ISSUED AT 333 AM CST MON FEB 8 2016

Long wave trof digging in over the Midwest, with good representation
on sat imagery this morning.  The deep trof over the eastern half of
the country will be the driving force through the end of the
forecast period. Variations and challenges in the forecast revolve
around subtle but significant nuances between models in handling the
trof.

For tonight, widespread light snow showers will remain the rule as
the sfc system makes its way through the region.  Models have been
relatively consistent with showing a showery nature to the
snowfall...and trying to show a bit of a break tonight before a
secondary wave comes in and develops another round.  Though most
places should see snow at some point, the qpf associated with this
storm is limited.  Lift is not that deep through the column, and the
moisture is also limited. Around a widespread inch or so could be
possible through Tuesday morning, with the higher inch to two totals
in the NE.  However light the snowfall totals are expected to be,
the blustery winds and cold temperatures will still result in a
travel menace with this snow.  15 to 20 mph winds gusting to 25 to
30 at times will result in some blowing snow and vis reductions, as
well as creating some slippery roads.

Chilly temperatures as Arctic air moves into the region behind the
snowfall, with Wednesdays highs only getting into the teens.  Mid
week is also about the time that the models start ejecting a series
of waves into the nwrly flow over the region.  GFS is quicker with
one on Wed afternoon, and the ECMWF is a little bit delayed into
early Friday.  Neither of the waves have much in the way of
confidence just yet as far as potential precip makers, but possibly
waves to help dig the trof further.  Which brings the forecast
around to the next big question...temperatures going into the next
weekend. ECMWF is far colder and deeper with another big surge of
Arctic air into the long wave that has remained over the eastern
CONUS for the entire forecast.  GFS is a little less aggressive.
Teleconnections forecast has the AO going negative, so the movement
of Arctic air into the CONUS is likely.  The GFS/ensemble forecast
for the NAO is positive, however, leaning to a weaker Icelandic low
and less amplified pattern over the eastern half of the country.
Less emphasis put on the GFS forecast with a which came first
argument.  The ensembles give a little more credit...but in reality,
the trend analysis alone in the teleconnections has been troublesome
this winter. The last situation that set up this way, the ECMWF
picked up on a deep cold trend before the GFS (and hence, the NAO
forecasts were also lagging). With all that in mind, have trended
the forecast slightly colder than the SuperBlend has into the
weekend, but not quite as aggressive as the incredibly cold ECMWF.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1203 PM CST MON FEB 8 2016

MVFR conditions will prevail through the entire 18z TAF
period...with occasional IFR visbys within heavier snow showers.
Models continue to suggest a break in the precip late this
afternoon and evening...and upstream obs across northeast
Iowa/southwest Wisconsin support this. As a result, have
temporarily ended snow showers after the 22z-00z time frame.
Another upper-level disturbance will pivot southward into the
region overnight, bringing a renewed round of snow showers. Based
on 12z NAM forecast, have brought precip back into the forecast
after 05z at KPIA...then after 09z further southeast at KCMI.
Winds will be strong/gusty from the northwest this
afternoon...gusting between 20 and 25kt at times. The gusts will
subside tonight...but sustained winds of 10 to 15kt will persist
through the night.

&&

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

$$

UPDATE...Barnes
SHORT TERM...Onton
LONG TERM...HJS
AVIATION...Barnes


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