Area Forecast Discussion
Issued by NWS Central Illinois

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693
FXUS63 KILX 251646
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1046 AM CST Sat Feb 25 2017

.UPDATE...
Issued at 1041 AM CST Sat Feb 25 2017

Deep upper low over the Great Lakes this morning bringing clouds
around the cyclonic flow over the region and providing just enough
lift for some continuing flurries. Between the clouds, some
sunshine starting to filter in and trying to bring the temps into
the upper 20s/lower 30s. May be a bit trickier in the north and
east where the cloud cover is still a little dense on vis Sat
imagery. Have made some very minor adjustments to the temperatures
and extended the flurry mention through the afternoon.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 331 AM CST Sat Feb 25 2017

Upper level trough axis currently over the area will move eastward
into Indiana by around sunrise as subsident area in a shortwave
ridge...currently evident on water vapor imagery over
IA/MN...reaches west-central IL. The result will be an end to
scattered light snow showers around or just after daybreak. The
colder air mass reaching IL this morning...evidenced by current
temperatures ranging from 23 in Galesburg to 35 in Lawrenceville...
will result in highs only reaching the 30s today for the first
below normal day in some time. Strong W-NW winds 15 to 25 mph with
gusts 30 to 35 mph will continue much of the day before tapering
off around sunset as a high pressure ridge finally nudges the
stiff pressure gradient eastward. The next low pressure system
moving into the upper Midwest will already start to increase
southerly wind by early Sunday morning...as south winds reach up
to 10 mph west of I-55. This will help to keep tonight`s lows
moderate...as only mid 20s expected.

.LONG TERM...(Sunday through Friday)
ISSUED AT 331 AM CST Sat Feb 25 2017

Main forecast issue will be timing of various shortwaves that will
be traversing the nation the upcoming week. Main upper flow will
start to come out of the southwest early in the week, as a wave digs
south from the Pacific Northwest. This will result in another period
of mild weather Monday-Tuesday, followed by retreating temperatures
as a more substantial upper wave pushes out of the Plains on
Wednesday.

Main effects of the first wave continue to target areas mainly south
of I-72 Sunday afternoon and evening, especially south of I-70. Some
flakes may mix in with the rain north of I-70 late Sunday night, but
should be of little consequence with the main precipitation shield
spreading across the Ohio Valley. More of a precipitation impact is
expected beginning Monday evening, as the next wave ejects northeast
out of the southwest U.S. Have maintained the likely PoP`s over most
areas Monday night, then the first part of Tuesday looks dry as a
storm system organizes over the central Plains and tracks northeast.
With most of the forecast area in the warm sector ahead of the
system, CAPE values off the GFS increase to around 500 J/kg in the
afternoon, warranting some thunder mention from about I-72 south.

Longer range models are in reasonable agreement with pushing a cold
front across the forecast area late Tuesday night and early
Wednesday, ahead of the significant upper trough over the Plains.
Main concern comes afterward, as the latest ECMWF is quite generous
with deformation type precipitation through Wednesday evening behind
the system. The GFS and Canadian models suggests some areas of light
precipitation Wednesday afternoon. However, all are more consistent
with steadier rains persisting south of I-70, as the front in that
area slows down as it starts to parallel the upper flow. As for the
deformation precipitation, leaned more toward the GFS for now and
went with slight chance PoP`s over the western CWA by afternoon.

As the trough broadens over the eastern U.S. later in the week, a
series of clippers will drop out of Canada, with the first arriving
Thursday afternoon/evening. The GFS is deeper with its moisture
profile, with the ECMWF more scattered with its precipitation.
Precipitation with this feature should largely be rain, with a
transition to snow as it is ending in the evening.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 524 AM CST Sat Feb 25 2017

Isolated snow showers and MVFR ceilings expected to end by 16Z
across central IL terminals with VFR conditions expected through
the remainder of the TAF forecast period. Winds WNW 16-22 kts with
gusts 25-32 kts until 00Z...decreasing to under 10 kts and
shifting to SSW.


&&

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

$$

UPDATE...HJS
SHORT TERM...37
LONG TERM...Geelhart
AVIATION...37



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