Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 102055
AFDILX

AREA FORECAST DISCUSSION
National Weather Service Lincoln IL
255 PM CST WED FEB 10 2016

.SHORT TERM...(Tonight)
ISSUED AT 255 PM CST WED FEB 10 2016

20z/2pm surface analysis shows 1011mb low over eastern Nebraska,
with frontal boundary extending southeastward into central Missouri.
Light to moderate snow has developed ahead of this feature from
central/southern Iowa into northeast Missouri and southwest
Illinois.  Latest radar imagery and surface obs show snow currently
falling along and southwest of a Macomb to Litchfield line.
Accumulations have thus far been quite light, with a few reports of
as much as half an inch in Greene County just south of Winchester.
Trajectory of radar echoes suggests the snow will skirt along the
southwest periphery of the KILX CWA late this afternoon through
evening before tapering off and coming to an end by midnight.  Have
adjusted PoPs to confine snow chances to along/south of a
Rushville..to Taylorville...to Olney line this evening.  Snow totals
will only amount to a couple tenths of an inch...with the heaviest
axis remaining further southwest from the St. Louis metro into
southern Illinois.  Further north across the remainder of the area,
cold and dry weather will prevail.  Overnight low temperatures will
mainly be in the single digits, with a few teens across the far SE.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 255 PM CST WED FEB 10 2016

The long wave trough in the eastern half of the CONUS will remain
through the weekend, with a couple of shortwaves triggering light
snow through next Monday. The primary periods of potential for snow
accumulation still look to be on Friday, and again on Sunday into
Monday. The below normal temperatures will remain in place until
early next week, when the upper ridge in the west shifts east into
Illinois, and surface temps are able to return above normal for mid-
week next week.

Thursday will start out with morning clouds south of I-72 as the
overnight weather disturbance and light snow depart to the
southeast. Sunshine is expected to develop for a majority of the day
across central and southeast IL. Despite the sunshine, high temps
will be limited to the lower 20s due to 850mb temps in the -8C to
-12C range.

Clouds will return quickly Thursday evening as a fast moving
shortwave brings a period of snow. The focus for precip looks to be
between midnight Thurs night and Noon on Friday, per the GFS, NAM
and Canadian GEM. The ECMWF dissipates the energy as the wave
reaches IL, producing little to no precip in our CWA. Will
continue with the consensus group for snow chances and light accum
less than one inch. NW winds will increase Friday afternoon as
another surge of Arctic air arrives, blowing around any light snow
that falls the previous 12 hours. Friday night lows will bottom
out in the single digits in our CWA, with steady NW winds through
the night. Wind chill values will approach advisory levels of -15F
for areas north of Peoria to Bloomington late Friday night and Sat
morning.

That Arctic surge will make Saturday our coldest day of the next
week, with highs only in the teens, and wind chills barely climbing
above zero by afternoon.

Varying model solutions for the next system for Sunday into Monday
has kept confidence low enough to prevent boosting PoPs into the
likely category. The ECMWF appears to be splitting the wave of
energy as it reaches Illinois, with little to no precip/snow accum
in our CWA. The GFS goes to the other end of the spectrum, producing
a surface low/surface circulation in north central IL as the upper
wave passes across IL. The NAM and Canadian are middle of the road,
with no distinct surface low, but they do produce some light snow in
our CWA with the shortwave. Keeping QPF on the lower end of the
compromise, we still could see a range of 1 to 3 inches of snow
across our forecast area. Upper end GFS numbers try to show
potential of 3-5" depending on snow ratios and snow algorithms.
Localized bands of snow could set up in an east-west orientation for
extended periods of time as the wave passes from west to east, if
the GFS solution verifies. WPC is showing 30% chance of 0.25" QPF in
the southern half of Illinois, which would support snow totals
toward the 3" amounts. Have kept our total QPF amounts between 0.14"
and 0.27", with snow amounts in the 1.8" to 2.8" range during the
Sunday into Monday morning 30 hour window. Obviously, confidence is
low, so as mentioned previously, PoPs were left in the higher end
Chance category, as indicated by the blended initialization.

Beyond that system, the longwave upper trough in the eastern CONUS
appears to shift east allowing the ridge in the western states to
progress into Illinois for Tues-Wed. Slight chances of rain/snow
were kept in the extended forecast from Mon night through Tues night
due to the ECMWF deepening a low SE of IL Monday night, and then the
GFS/ECMWF bringing a clipper north of our CWA Tues night. At least
high temps are forecast to climb into the upper 30s and low 40s Tues
and Wed, providing some relief from the recent period of cold
conditions.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1153 AM CST WED FEB 10 2016

VFR conditions will prevail through the entire 18z TAF period.
High clouds have spread across all of central Illinois late this
morning in advance of a fast-moving storm system tracking
southeastward out of the Northern Plains. This feature will
remain largely west and south of the area: however, lower
ceilings and perhaps a period of very light snow is expected at
KSPI later today. Based on 12z NAM forecast soundings and latest
satellite/radar loops...have decreased ceilings to 3500ft and
introduced VCSH at KSPI between 23z and 06z. Once the system
passes by to the south, mid-level cloud deck will gradually
dissipate late tonight into Thursday morning. Winds will remain
light, generally from the W/NW at 10kt or less.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Shimon
AVIATION...Barnes


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