Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 020758

Area Forecast Discussion
258 AM CDT Thu Oct 2 2014

.SHORT TERM...(Today)

06z/1am surface analysis shows warm front extending from central
Missouri eastward into the Ohio River Valley.  Several clusters of
convection have been tracking along/north of the front overnight,
aided by a 30-35kt 850mb jet streak oriented from the Southern
Plains northeastward across the boundary.  This activity will
continue for the next few hours, but should begin to wane by
mid-morning as front lifts further northward.  Based on current
radar trends and 00z model data, will carry likely PoPs
along/northwest of I-70 through midday, with only chance PoPs
further south.  Meanwhile, low pressure developing over Oklahoma
will track northeastward into southern Wisconsin by this evening.
Line of thunderstorms is expected to develop along/ahead of
associated cold front, with most model solutions keeping this
convection just west of the KILX CWA until late afternoon/early
evening.  Have increased PoPs to categorical across the Illinois
River Valley this afternoon in case storms get going faster than
anticipated, but think bulk of activity will hold off until
evening.  Aside from the rain chances today, it will be another
very warm day with highs ranging from the middle 70s far northwest
around Galesburg to the middle 80s along/south of I-70.


.LONG TERM...(Tonight through Wednesday)

Latest Day 1 convective outlook from SPC places all of
central/southeast Illinois under a slight risk for severe weather
tonight.  With a very warm/humid airmass surging northward ahead of
an approaching cold front, resulting CAPE values will likely
exceed 1500J/kg later today.  In addition, low-level wind shear
will be increasing with 0-6km bulk shear values generally in the
30-40kt range.  These favorable parameters combined with strong
convergence along the cold front will lead to the development of a
line of thunderstorms this evening.  Models generally develop the
storms along the Mississippi River by late afternoon, then push
them eastward to the I-55 corridor by mid-evening and into
east-central Illinois shortly after midnight.  Main severe weather
threat will be strong/damaging winds, although highest
probabilities for widespread severe will likely remain further
southwest from the St. Louis area southwestward to Texas.  With
precipitable water values climbing over 1.75, high rainfall rates
will be likely with any storms that develop.  Localized flash
flooding may develop within the strongest storms: however, recent
rainfall amounts have not been great enough over a wide enough
area to warrant a Flash Flood Watch at this time.

Front will push into Indiana by Friday morning, bringing an end to
the greatest rain chances.  Still some model discrepancy concerning
timing of frontal departure, with the ECMWF being the slowest.  Have
therefore hung on to chance PoPs early Friday morning along/east of
I-57.  A secondary upper wave currently evident on water vapor
imagery over Alberta will dive southeastward Friday
afternoon/evening, amplifying the mean trough over the Great
Lakes/Midwest.  Synoptic lift and steep mid-level lapse rates
associated with this feature will be enough to warrant a slight
chance for showers, mainly during the afternoon.  Main weather story
on Friday will be the windy and sharply cooler conditions.
Tightening pressure gradient between departing front and approaching
Canadian high pressure will lead to strong W/NW winds gusting to
between 30 and 35mph.  Temperatures will struggle to rise much at
all from morning lows, with readings remaining in the 60s.

With 850mb temps progged to drop into the -3 to -5C range, low
temperatures by Saturday morning will fall into the middle
30s...representing a nearly 50 degree temp drop from expected high
temps today! Due to a continued brisk northwesterly breeze, am
not expecting any frost to develop Friday night.  Heart of cold
airmass will be in place across Illinois on Saturday, with highs
struggling to reach the middle to upper 50s and overnight lows
once again dropping into the middle to upper 30s.  With much
lighter winds expected, a few patches of frost will be possible by
Sunday morning, especially if skies can remain clear ahead of the
next approaching short-wave trough.

After that, the Midwest will be dominated by northwesterly
upper-level flow through Tuesday before trough retreats into Canada
by the middle and end of next week.  This will mean continued below
normal temps in the 60s through Tuesday, followed by a warming trend
and a return to the 70s by Wednesday and Thursday.


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

Periods of showers and some thunderstorms are expected through the
rest of the night across the central Illinois terminals, although
the thunderstorm threat should be more spotty at KPIA & KBMI. Have
covered thunder threat with a VCTS and/or a tempo group overnight.
VFR conditions should fall to MVFR or briefly IFR during steadier
rainfall. A break in the precipitation threat is expected early
Thursday as the warm front (responsible for tonight`s
showers/storms) lifts north of the area. Then, chances for
showers/storms return Thursday afternoon, and especially Thursday
evening, as a cold front pushes in from the west. For now, have
covered these storms with predominant showers and a VCTS. However,
expect thunder chances to increase in later TAF issuances as the
coverage is more clear. The heavier rainfall ahead of the cold
front tomorrow should eventually result in widespread MVFR and/or
IFR conditions by evening.




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.