Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 241758
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1158 AM CST Tue Feb 24 2015

.UPDATE...
ISSUED AT 959 AM CST TUE FEB 24 2015

Water vapor satellite and radar images are showing a compact
shortwave diving east-southeast across southern Wisconsin this
morning. The wave will pass across northern Illinois this
afternoon, triggering snow showers mainly north of our forecast
area. Increasing clouds and a few flurries could extend as far
south as the I-74 corridor this afternoon, which is handled well
in the weather grids. The shortwave is preceding a warm front
approaching from the west. Strong southwest winds ahead of the
front will bring a significant warm-up from the very cold air
early this morning. Some locations in our eastern counties dipped
to -12 to -20F for low temps this morning. They could recover into
the upper 20s for highs today, with western locations near
Jacksonville into the mid 30s. However, the gusty winds will make
it feel much colder. Only minor adjustments were needed for the
temperature, sky and wind grids today, which are already
available.

&&

.SHORT TERM...(Today)
ISSUED AT 311 AM CST TUE FEB 24 2015

High pressure centered over the Ohio River Valley will continue to
slide off to the southeast, allowing a frontal boundary to approach
from the northwest.  A tightening pressure gradient between these
two features will create strong southwesterly winds gusting to
between 20 and 30 mph from late morning through the afternoon.
Clouds will be on the increase as the front gets closer, and there
will be enough lift to warrant a chance of flurries across the
northern half of the KILX CWA this afternoon.  Due to partial
sunshine and the strong southwesterly flow, afternoon high
temperatures will be considerably warmer than in recent days, with
readings topping out in the lower to middle 30s.

&&

.LONG TERM...(Tonight through Monday)
ISSUED AT 311 AM CST TUE FEB 24 2015

Plenty of challenges in the extended...including a clipper system
Wednesday night into Thursday, as well as the potential for a
long-duration precipitation event late in the weekend into early
next week.

Low pressure currently over northern Alberta will dive southeastward
over the next 36 hours, spreading clouds and light precipitation
into the area Wednesday night.  00z Feb 24 models exhibit a slight
northward shift in its track, with consensus placing it near Kansas
City by Wednesday evening.  Low will be gradually dissipating as it
moves further E/SE: however, its more northerly track means precip
will likely spread further north and east into the area than
previously thought.  Still think heaviest precip will be centered
along/north of the 500mb vort max, generally across the W/SW CWA.
Based on new QPF guidance from WPC and using a 15:1 snow to water
ratio, around 1 inch of snow can be expected along/west of a Peoria
to Springfield line with as much as 2 inches possible further west
toward Quincy/Macomb.  Further east, lighter amounts of less than 1
inch can be expected across the remainder of the area.  Despite the
dissipation of the clipper, a secondary upper wave is now apparent
on model solutions swinging into the area on Thursday.  Enough
synoptic lift will be present along/ahead of this wave to warrant
low chance PoPs for light snow-showers, although little or no
additional accumulation is anticipated.

After a period of cold/dry weather Friday and Saturday, things get
more complicated late in the weekend as the upper air pattern shifts
from northwesterly to southwesterly.  It is looking increasingly
likely that a baroclinic zone will lift northward into the region
and stall as it becomes parallel to the upper flow.  Numerous waves
are expected to track along the boundary, setting the stage for a
long-duration precip event.  There are still many questions
regarding timing of individual waves, but general model consensus
points to an unsettled period from Saturday night through at least
Sunday night.  There are even some indications that additional waves
will prolong the unsettled weather into Monday and Tuesday as well.
At this time, will take a conservative approach due to model
uncertainties during this major pattern change and stick with the
main precip event occurring from Saturday night through Sunday
night.  Airmass will initially be very cold/dry, so think precip will
hold off until Saturday night and will begin as all snow across the
area.  As warmer air tries to work northward, precip type becomes a
concern on Sunday.  High temperatures will likely rise above
freezing across the board, with areas along/south of I-70 reaching
the 40 degree mark.  As a result, the snow will change to all rain
across the SE CWA by Sunday afternoon and to a rain/snow mix across
much of the remainder of the area.  Locations across the far north
from the Peoria area northward may remain all snow through Sunday.
As the baroclinic zone slowly shifts eastward Sunday night into
Monday, precip chances will gradually diminish from northwest to
southeast.  The rain/snow mix will transition to light snow
everywhere Sunday night before largely coming to an end on Monday.
It is still too early to discuss snow accumulations, but the
potential certainly exists, particularly Saturday night into Sunday
morning.  Will also have to keep an eye on the potential for a
secondary wave along the boundary that could pull precip back into
the area Monday night into Tuesday.  All in all, the extended is
shaping up to be quite active.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 1159 AM CST TUE FEB 24 2015

Breezy sw winds of 15-20 kts with gusts in the 20s will occur this
afternoon ahead of a cold front dropping se from the northern
plains into central IL this evening. Some high end MVFR ceilings
are possible over mainly northern airports along I-74 from mid
afternoon into early evening along with chance of flurries. Light
snow showers should stay north of central IL this afternoon and
early evening. Lower clouds scatter out behind cold front during
mid/late evening and then high clouds increase overnight with mid
level clouds arriving during mid/late Wed morning ahead of next
clipper low pressure system dropping se into eastern Nebraska by
18Z/noon Wed. Winds will veer west this evening and diminish to
between 5-10 kts by mid evening and then nw overnight. Winds veer
ene 5-9 kts Wed morning.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...07




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