Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260927

Area Forecast Discussion
327 AM CST Mon Jan 26 2015

.SHORT TERM...(Today)

Latest surface analysis indicating weak high pressure centered from
central lower Michigan southwest through northeast Missouri. Our
next weather system was already producing some light snow across
parts of central Minnesota...which was tracking southeast early this
morning. The main short term forecast concern will be with this weak
upper level system that will track across our area today and the
precip chances with it.

Models have trended a bit further south and west with the upper wave
along with the fairly compact area of lift associated with it.
Forcing in the 700-500 mb layer compact but short lived with this
system and based on the latest HRRR and RAP solutions, it appears
the threat (20-30 POPs) for light snow will track southeast into our
area later this morning and then shift into east central Illinois by
this afternoon and evening. Forecast soundings have all trended a
bit deeper with the moisture with this system and cold enough to
support light snow except over far southwest Illinois where there
may be a mix of rain and snow for a few hours as surface temps rise
into the middle 30s.

Despite the decent low to mid level forcing with this wave, QPF
amounts will be light with any snow accumulations of less than an
inch. As the better forcing shifts off to our east, we start to lose
the ice crystals in the upper levels of the clouds that would support
mainly light snow. Nam time-height cross sections showing some very
weak lift tracking thru the area late this afternoon in the 925-850
mb layer so not the greatest setup for freezing drizzle but will
need to be watched later this afternoon and evening.


.LONG TERM...(Tonight through Sunday)

Elongated short wave will gradually shift east of IL by dawn Tuesday
with light snow chances shifting east of IL into Indiana. Low clouds
will be slow to clear from the west however on Tue with mostly
cloudy skies generally prevailing, with IL river valley having
better chance of becoming partly sunny during Tue afternoon.
Seasonable highs in the middle to upper 30s Tue with north winds 8-15
mph. Low clouds to continue to decrease Tue night as weak surface
high pressure ridge sets up over IL by Tue evening. Lows Tue night
in the lower to middle 20s.

Upper level ridging into IL Wed will give partly to mostly sunny
skies, while 1005 mb surface low pressure moving east into the
central plains Wed to give breezy sse winds of milder air into the
region with highs in the 40s Wed (ranging from lower 40s ne counties
to near 50F from Jacksonville sw). Low pressure to move east across
central IL during Wed night and bring a chance of light rain with
lows staying above freezing in the mid to upper 30s. Light rain
chances to diminish from west to east during Thu and could see light
snow chances too over northern counties before ending as cooler air
arrives on back side of low pressure moving into the southern Great
Lakes region. Highs Thu range from upper 30s to near 40F IL river
valley to upper 40s in southeast IL.

Dry conditions and cooler temps return to central/se IL from Thu
night thru Fri night as high pressure settles into the ohio river
valley by Friday evening. Highs Fri back to seasonable levels for
late Jan in the mid to upper 30s. Continued slight chances of light
snow Sat and Sat night as cold front moves through. A cutoff upper
level low in the sw states late this week will move east and keeps
brunt of its qpf south of central IL, though some models have us on
northern edge of ligher qpf this weekend. Also have a northern
stream clipper system moving through the Great Lakes Sat and Sat
night that drives a cold front through IL. May need to increase
chances of light snow this weekend, though timing issues and also
question if any phasing can take place bettern stronger southern
stream system and weakern northern stream short wave. Also southern
areas could see a mix of precipitation on Sat before colder air
arrives Sat night. MEX/GFS appears too warm with temps behind cold
front Sun/Mon and oddly doesn`t cool it off much from Sat. ECWMF/ECE
model cools off much more Sun/Mon. Did not go as cold as this model,
but have temperatures dropping from highs in upper 30s to around 40F
Sat to the upper 20s/lower 30s Sunday.


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

Clearing area associated with weak ridge building into Illinois
has slowed its southeast progress near I-55. High clouds from
next cliper system already beginning to cross Mississippi River
and will likely overspread sites experiencing clearing over next
few hours.

NAM from 00z suggests that partial clearing will resume its
progress slowly southeast after 06z, but that will be followed by
MVFR deck from next system during the day Monday. Model suite from
00z a bit further south with low measurable pops and impacts all
TAF sites at one time or another. Forecast soundings suggest that
there may still be some potential for FZDZ given the dry air in
crystal formation layer. Will include about a 4-hr tempo group for
I-74 terminals for -SN at this time but later shifts will need to
monitor closely.

Winds are diminishing quickly as the gradient weakens as the
surface ridge moves in. Winds should shift around to the south
Monday and then back to the northwest after the cold front passage
associated with the cliper which will likely be just beyond the
valid time of this set of terminals.





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