Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 291807

Area Forecast Discussion
1207 PM CST Thu Jan 29 2015


Only minor updates were made to the forecast for this afternoon in
central and southeast Illinois. The latest satellite loop shows
plenty of cloud cover upstream, so cloudy conditions will prevail
until at least tonight. There is a weak shortwave embedded in the
northwest flow across southeast Iowa. This should bring a period
of drizzle to west central Illinois early this afternoon, so
included that in the forecast west of I-55.

A steep pressure gradient will keep windy conditions in place this
afternoon, especially in central and eastern IL. Increased the
gusts slightly in a few places, otherwise the current forecast has
a good handle on the gusty northwest winds.

The cloud cover and weak low level cold advection will keep
temperatures fairly steady through the afternoon in the 35-40
range across the entire area.


.SHORT TERM...(Today)

Low pressure centered just north of Moline at 08z/2am will continue
to push east and drag a cold front through our area this morning.
Warmest temperatures will be just ahead of the cold front early this
morning, and then we expect temperatures to fall off quickly just
behind the cold front during the remainder of the morning, and then
hold fairly steady this afternoon. Winds will be gusty again today
but this time out of the northwest with a few gusts of 35 to 40 mph
at times about an hour or two after frontal passage right along the
stronger surface pressure rises. Look for gusts in the 30 to 35 mph
range this afternoon.

Not seeing a lot of precip, other than some occasional very light
rain/drizzle out in Iowa so will continue with just a slight chance
of light rain/snow this morning with POPs decreasing from west to
east this afternoon, and that would be mainly across the north half
of the forecast area. Latest satellite data and upstream surface
observations not showing much hope for any clearing across our area
in the near term. Forecast soundings off the NAM-WRF showing a
fairly strong subsidence inversion setting up again in the wake of
this system resulting in quite a bit of low level moisture trapped
beneath the inversion at around 2500-3000 feet. As a result, we have
backed off with any decrease in cloud cover until later this evening
and that may be optimistic based on the latest (06z) forecast
soundings off the NAM.


.LONG TERM...(Tonight through Wednesday)

Short wave trof to exit east and se of IL early this evening as
Canadian high pressure over the Canadian Rockies settles into the
upper Midwest tonight. However an inversion will likely trap low
level clouds longer tonight and have trended the forecast slower
with decreasing low clouds from the west. Low clouds could linger
over ne counties into Friday morning especially near IN border.
Cooler lows tonight in upper teens to near 20F northern areas to mid
20s in southeast IL. Brisk nw winds 15-25 mph this evening to slowly
diminish during overnight into Friday morning as high pressure
settles into IL on Friday. Highs Friday 29-35F with coolest readings
from I-74 ne with partly to mostly sunny skies.

High pressure settles into the Ohio river valley Friday evening and
into central Appalachians by dawn Sat and continue fair/dry weather
through at least Saturday morning. Lows Friday night in upper teens
and lower 20s again. Milder highs Sat in upper 30s and lower 40s
with mildest readings sw areas with ssw breezes. Clouds to increase
later Friday night into Sat ahead of next storm system with slight
chance of light rain/snow later Saturday afternoon west of I-55. Most
over central and especially eastern IL should still be dry through the
daytime hours on Saturday.

12Z Jan 28 forecast models trended further south with low pressure
system Sat night and Sunday, while 00Z Jan 29 forecast models have
trended back north with more phasing of southern and northern stream
upper level systems, along with higher snowfall amounts over central
and southeast IL. 00Z models have also trended colder with even
southeast IL looking like all snow with this eveng and mixed
precipitation south of I-64 toward the ohio river. Confidence is not
too high yet with this potentially high impact winter weather event
with extended period of overrunning snow developing Saturday night
and continue through Sunday before diminishing Sunday night. Several
inches of snow still appears possible over central and southeast IL.
Canadian high pressure settles into IL Monday returning dry and
colder weather. A northern stream short wave races ese into Great
Lakes region late Tue and Tue night bringing small chances of light
snow with best chances ne of central IL. Another Canadian high
pressure settles into region by Thu brining in even colder air. So
after above normal temps overall since mid Jan, next week (first
week of Feb) looks like temps will likely be below normal.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)

The main aviation concerns will be with MVFR ceilings and the
strong northwest wind gusts across central and eastern Illinois.

The latest satellite loop and surface observations indicated a
large area of MVFR ceilings across all of Illinois and much of
Iowa. The main question is the advancement of an area of partial
clearing from southern MN and central IA, and when the MVFR
ceilings will dissipate. The vast majority of short range models
indicate that a shortwave trough axis will swing through central
and eastern IL late this evening. However, most of these same
models including the NAM, RAP and HRRR indicate that there will be
plenty of low level moisture trapped below a stout inversion. This
would keep at least broken MVFR ceilings in the area through the
night and into much of Friday morning. Will follow this line of
thinking as it can be very difficult to erode low level clouds
this time of year.

The tight pressure gradient will keep northwest winds gusting
around 25-30 knots through the afternoon into early evening at
most TAF sites - particularly in east central Illinois. The
lessening impact of the surface low moving through the eastern
Great Lakes will result in diminishing wind in central IL late
this evening, and in eastern Illinois before daybreak.




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