Area Forecast Discussion
Issued by NWS Central Illinois

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KILX 240929

Area Forecast Discussion
329 AM CST Mon Nov 24 2014

.SHORT TERM...(Today)

Several short-term forecast challenges today, as a potent storm
system tracks through the area.  Of particular concern are
strong/gusty winds behind a departing frontal boundary and the
potential for a light accumulation of snow across the W/NW KILX

08z/2am surface analysis shows cold front extending from southern
Lake Michigan to the Ozarks.  An area of low pressure along the
boundary over southeast Missouri is currently enhancing lift and
triggering a few thunderstorms along/south of the I-70 corridor.
This activity will push E/NE into Indiana by dawn.  Further west, an
area of precipitation along/behind the front will continue to lift
northward, mainly impacting locations along/west of I-57.  As colder
air streams into the region, the rain will gradually mix with and
change to snow by mid-morning.  Based on upstream temp falls across
Iowa/Missouri, readings will drop into the middle 30s across the
Illinois River Valley by 12z/6am, then further east to the I-55
corridor by 15z/9am.  At the same time, the precip will be pulling
northeastward out of the area, so there appears to be only a narrow
window of opportunity for snow across the W/NW.  Will carry likely
to categorical PoPs across the western half of the CWA for rain
changing to snow this morning, with lower rain chances further east
and south across the remainder of the region.  Main area of snow
will lift into northern Illinois by midday, with only a few
flurries/snow-showers persisting along/north of I-72 this
afternoon.  Total snow accumulation will be limited due to light QPF
and marginally favorable temps.  Around 1 inch is expected
along/north of a Canton to Bloomington-Normal line, with trace
amounts as far southeast as a Litchfield to Champaign-Urbana

Other big story today will be the strong winds behind the cold
front.  Upstream obs have already shown gusts as high as 30-40mph
and think these will translate eastward across central Illinois this
morning.  Main question will be whether there may be a corridor of
enhanced winds approaching Wind Advisory criteria across the E/SE
CWA.  Current MSAS analysis shows max 3-hour pressure rises of 6mb
over southern Missouri/northern Arkansas.  Both the 00z and 06z runs
of the NAM have shown these rises tracking northeastward and
increasing to around 9mb over southeast Illinois later this
morning.  HRRR 10m wind gust graphic also indicates increasing winds
ahead of the pressure change couplet as it moves across the
southeast CWA between 12z and 18z.  Given this consistent signal,
think it is prudent to issue a Wind Advisory for locations
along/southeast of a Champaign to Taylorville line.  While all of
central Illinois will experience wind gusts of 30 to 35 mph, this
particular area may see higher gusts exceeding 40 mph.


.LONG TERM...(Tonight through Sunday)

Low pressure will lift into the Great Lakes tonight, taking the bulk
of the precip with it.  Wrap around moisture may brush across the
northern CWA, so have included scattered flurries in the forecast
this evening along/north of I-72.  Forecast soundings indicate low
clouds will persist tonight and may even be slow to clear on
Tuesday, despite approaching surface ridge axis.  Have therefore
slowed the clearing trend, with cloudy skies tonight followed by
decreasing clouds on Tuesday.

Fast-moving clipper system is still on target for mid-week, with
model consensus bringing the system across central Illinois on
Wednesday.  This particular track is slightly further south than
previously advertised, so WAA ahead of the wave may not be quite as
pronounced as once thought.  Even still, high temperatures will
climb well into the 30s and into the lower 40s across the southeast
CWA.  End result will be light snow across the far north from the
Peoria area northward, a mix of light rain/snow across much of the
area, and mainly rain south of I-70.  Due to the limited period of
light precip and warm temps, snow accumulations will be minimal.
Once this system passes to the east, another shot of cold air will
arrive for Thursday.  After that, signs are still pointing to warmer
conditions by the end of the week, with temps climbing well into the
40s by Saturday.  Both the GFS and ECMWF indicate a cold front will
drop through the region Saturday night, so temps will likely drop
back into the upper 30s/lower 40s by Sunday/Monday.  Moisture will
be limited, so will maintain a dry FROPA at this time.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)

The pair of surface low centers have merged and lifted to the NE
of our forecast area, with a trailing cold front to the SW across
IL into southeast Missouri. Drizzle, fog and low clouds are
lingering behind the departing low along that trough, with VLIFR
ceilings at BMI, and LIFR ceilings at the remaining TAF sites.
Expect ceilings to improve slightly with the return redevelopment
of showers well behind the low, but remaining LIFR until Monday
afternoon when levels possibly climb all the way to MVFR.

Cold air will filter into central IL late tonight and Monday
morning, causing the rain showers to mix with or change to light
snow from west to east toward 6 am for PIA/SPI, 8 am for BMI, and
10 am for CMI/DEC. As the precipitation becomes all snow, vsbys
could drop below 1 mile at PIA and BMI where snowfall accumulation
could climb up as high as 1 inch. Vsbys should remain 2-4 miles
farther south toward I-72 where snowfall will be lighter. Snowfall
rates will diminish quickly after 18z-19z, with high winds blowing
any snow around and possibly keeping visibility low at times.

Winds have already become SW behind the low. Pressure rises will
climb to 6 mb/3 hours in at least the southeast half of our
forecast area, which would include DEC/CMI. Wind speeds in our
southeast areas could climb as high as 30g40kt between 12z and 15z
this morning, with other areas 25g35kt. Those speeds could
continue into early afternoon, but we should see some decrease in
peak gusts as the afternoon progresses.


WIND ADVISORY until 6 PM CST this evening FOR ILZ044>046-052>057-



LONG TERM...Barnes
AVIATION...Shimon is the U.S. government's official web portal to all federal, state and local government web resources and services.