Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 121130

Area Forecast Discussion
National Weather Service Lincoln IL
630 AM CDT Sat Apr 12 2014

ISSUED 306 AM CDT Sat Apr 12 2014

SHORT TERM...Today through Monday

A windy and very warm day is in store across central Illinois
today. An old frontal boundary currently draped across central
Missouri into the Ohio River Valley will lift rapidly northward
this morning, bringing increasing southerly winds and low-level
moisture. Impressive dew point gradient currently evident across
the region, with middle 30s observed north of the boundary across
central Illinois rising to the lower to middle 50s south of the
front across southern Missouri into western Kentucky. Thanks to
a tightening pressure gradient, strong southerly winds will
transport this moisture northward into central Illinois this
afternoon, pushing DEWPOINTS into the middle to upper 50s.
Forecast soundings and BUFKIT data suggest wind gusts of 30 to
35mph later today. With partly sunny skies and strong southerly
flow, high temperatures will be a couple of degrees warmer than
yesterday, with most locations topping out in the middle to upper

Two upper air features will play a major role in the weather
across the Midwest over the next 48 hours. The first is a cut-off
low currently spinning over southern California, and the second is
a northern stream wave dropping southeastward toward the northern
Rockies. As the cut-off low opens up and is ejected eastward,
surface cyclogenesis will take place over the Oklahoma panhandle
later today into tonight. Increasing LLJ ahead of the approaching
low will allow convection to blossom within the strongest
instability axis across Kansas into central/northern Iowa late
this afternoon/evening. While decent CAPE values of around
1000J/kg will develop further east across central Illinois today,
forecast soundings show a strong cap at around 750mb. Due to the
capped air mass and lack of strong forcing, will go with a dry
forecast across the board through this afternoon. As surface low
and its associated frontal boundary slowly edge eastward,
showers/storms will begin to develop across the western KILX CWA
tonight. Models have trended slower with the eastward spread of
the precip, so will confine PoPs to locations along/west of the
I-55 corridor. System makes only slow progress eastward on Sunday,
with NAM/GFS/ECMWF showing little or no precip across the far
E/SE. Have made a few adjustments to PoPs in order to account for
the slowing trend, with areas along/south of I-70 remaining dry
throughout the day Sunday. Further west, will go with categorical
PoPs in the Illinois River Valley in closer proximity to strongest
forcing. Will be another very warm day, with highs ranging from
the rain-cooled upper 60s west of the Illinois River to the upper
70s far SE.

Best rain chances arrive Sunday night as initial upper wave pushes
cold front into the area. With strong convergence along the
surface front, ample support aloft, and precipitable water values
climbing to around 1.50, widespread showers and thunderstorms are
a good bet. Locally heavy rainfall will be likely as well. Cold
front will push into Indiana by Monday morning, resulting in windy
and sharply colder conditions. High temperatures will only be in
the 40s across much of the area, with early morning highs in the
upper 50s to around 60 across the Wabash River Valley dropping
into the 40s as the day progresses. In addition, all models
indicate lingering showers well behind the boundary as northern
stream upper wave arrives. Big question will be whether or not any
moisture can linger long enough to change to snow Monday night as
850mb temps drop into the -4 to -8C range and surface temps drop
into the upper 20s/lower 30s. At this point, the NAM is the only
model that is showing snow across central Illinois, as it develops
a secondary low along the departing cold front. GFS/ECMWF/GEM do
not develop this feature and thus bring the precip to an end
before the air mass cools sufficiently for snow. As a result, will
only carry a slight chance for rain showers during the evening
across the E/SE CWA, followed by cold and dry weather overnight.

LONG TERM...Tuesday through Friday

Mainly quiet weather can be expected in the extended, with a
gradual warm-up. Rising upper heights will allow chilly temps in
the 40s on Tuesday to recover into the 60s by Thursday and Friday.
Models are having trouble resolving the next potential system to
impact the region by the end of next week, with the GFS being much
more aggressive with precip Thursday night into Friday. Due to
discrepancies this far out, will only mention a slight chance for
showers on Friday until better consensus is reached.



ISSUED 630 AM CDT Sat Apr 12 2014

Southerly winds will ramp up quickly this morning as mixing takes
place, with gusts of 25-30 knots likely by late morning,
continuing into the afternoon. The gusts should begin to drop off
early this evening, but sustained winds of 10-15 knots still
likely through the night. Will need to watch for potential for
LLWS, with some of the models hinting at some borderline LLWS
conditions by mid evening, but will hold off on including it for
now. Ceilings so far today have been VFR, but as low as around
4000 feet near KDEC. HRRR guidance continues to suggest a period
of around 3500 feet through late morning, before rising toward
early afternoon.

Shower and thunderstorm trends are more uncertain, as the incoming
cold front slows a bit. Latest model guidance suggests the period
after 06Z is most likely to see anything, but the showers/storms
that will develop west of the Mississippi River this evening will
likely be breaking up as they approach central Illinois. Have
included some VCSH mention at KPIA/KBMI/KSPI for late in the TAF
period, but kept it dry further east.




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