Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 221645

Area Forecast Discussion
1045 AM CST Sat Nov 22 2014


Will update the forecast for warmer highs this afternoon as
temperatures running warmer, especially in far southeast IL with
Mount Carmel airport up to 61F at 10 am and Lawrenceville at 57F.
Much milder highs in the mid 50s to lower 60s, and mildest day
since Veterans Day Nov 11. Isolated to scattered rain showers to
occur mainly se of the IL river rest of today.

Breaks in low clouds by late morning especially along and south of
a Rushville to Lincoln to Champaign line. Isolated showers were
east of I-57 in eastern IL and lifting ne into Indiana. A few
showers and isolated thunderstorms was over southern MO and these
could lift ne into sw counties and southeast IL by this evening.
SPC has general risk of thunder later today sw of a Quincy to
Springfield to Taylorville line. Breezy ssw winds 12-18 mph and
gusts 18-25 mph bringing milder air in the upper 40s to mid 50s
(coolest readings ne counties), with Mount Carmel airport up to 61F.


.SHORT TERM...(Today)

Widespread showers associated with a passing short-wave have now
lifted N/NE into northern Illinois, leaving behind only isolated
showers across the KILX CWA early this morning.  Central Illinois
will remain between the departing wave and a much stronger upstream
system today, resulting in limited synoptic lift and overall low
rain chances.  In addition, forecast soundings indicate quite a bit
of mid-level drying in the wake of the initial short-wave, so
deep-layer moisture will be lacking for precip development as well.
As a result, have reduced PoPs into the chance category, with mainly
just very light showers or drizzle noted.  Brisk southerly winds
will continue to bring warmer air into the region.  Based on current
rate of temp rise, have gone at or above the warmest guidance
numbers, with afternoon highs reaching the lower to middle 50s.


.LONG TERM...(Tonight through Friday)

After a lull in the precip today, rain chances will once again begin
to increase tonight as another short-wave approaches from the
southwest.  After a full day of southerly flow, much deeper moisture
profiles will be in place by the time this particular feature
arrives.  As a result, think showers will become likely across the
board overnight.

Main forecast challenges continue to revolve around the phasing of a
vigorous southern stream wave currently evident on water vapor
imagery over northwest Mexico and an approaching northern stream
system.  The NAM is the only model that tends to keep the two
systems separate, so have rejected its solution in favor of the
GFS/ECMWF/GEM consensus.  End result will be the development of
surface low pressure over Texas Saturday night that lifts
northeastward into Michigan by Monday morning.  This particular
track will take the low along/east of the I-57 corridor Sunday
night.  After the Saturday night wave exits the region, another
brief lull in precip chances may occur early Sunday morning before
much stronger lift arrives with the main system Sunday afternoon.
Given strong upper dynamics and copious amounts of atmospheric
moisture, will go with categorical PoPs across the board Sunday into
Sunday evening.  While the strongest surface-based instability will
remain well to the S/SE from the Tennessee River Valley southward to
the Gulf Coast, think marginal elevated instability in the vicinity
of the deepening low pressure will be sufficient to mention isolated
thunder along/south of I-70 Sunday afternoon and evening.

Once low moves into the southern Great Lakes, strong CAA will spill
into the region late Sunday night into Monday.  Most model solutions
agree that the cold air will arrive before the precip has a chance
to depart, so will continue to feature rain/snow-showers mainly
along/west of I-55 late Sunday night into Monday morning before the
low lifts further to the northeast and precip comes to an end.

After that, cold and generally dry weather will be on tap for the
remainder of the week.  The only potential fly in the ointment is a
weak clipper system expected to come through by mid-week.  Models
still show some minor timing discrepancies: however, signs are
pointing to Wednesday as the most favored time period for light
precip.  WAA ahead of the approaching wave will likely boost temps
into the middle to upper 30s across much of the area, with lower 40s
possible far southeast. Given cold air aloft, will carry low chance
PoPs for light snow across the western half of the CWA Wednesday,
then across the east Wednesday night.  Due to the weak/fast-moving
nature of this system and the marginally warm temps, am not
expecting much in the way of snow accumulation, with perhaps a
couple tenths of an inch at best.  Thanksgiving Day still looks
cold and dry with highs ranging from the upper 20s north to the
middle 30s far south.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)

Strong warm/moist advection in advance of an approaching storm
system will produce periods of showers/drizzle across the central
Illinois terminals through the 12Z TAF valid time. Conditions will
rapidly degrade to MVFR and eventually IFR where they have not
already done so. For the majority of the period, there is not a
strong focus to say explicitly when rainfall will occur, and covered
majority of the period with a VCSH. Went with prevailing
rain/drizzle later tonight as a piece of upper energy arrives,
and as forecast soundings suggest a deepening moisture depth. A
strong low level inversion will keep surface winds less gusty than
they otherwise might be, but during the non-peak heating times
where gusts are not occurring, LLWS will be a concern.





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