Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 042317
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
617 PM CDT Mon Jul 4 2022

.SYNOPSIS...
Issued at 606 PM CDT Mon Jul 4 2022

Heat and humidity will build across central Illinois on Tuesday as
afternoon high temperatures soar into the middle to upper 90s and
heat index values reach dangerous levels approaching 110 degrees.
While a stray thunderstorm cannot be ruled out, it appears the
better chances for storms will hold off until Wednesday and
Thursday.

&&

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 342 PM CDT Mon Jul 4 2022

A warm front associated with a surface low over the central Plains
had made it to a line from near Peoria to Champaign as of 2 pm
CDT. North of the front, convection was growing in strength with a
severe storm moving southeastward just to the north of the ILX
forecast area, and scattered non-severe showers/storms extending
down into Woodford County. Northern portions of the ILX forecast
area may be affected as this activity continues to the east. With
around 1500 J/kg of MLCAPE and 30-40 kt of 0-6 km shear, storms
could continue to strengthen. Shear drops off fairly quickly with
southward extent and the thermodynamic profile is not as
favorable, so the northern portions of the ILX forecast area are
the spot to watch over the next few hours per SPC probabilities.

CAMs depict activity decreasing rather quickly this evening, with
south winds continuing and temperatures remaining elevated in the
very moist environment. The majority of CAM solutions initiate a
line of strong thunderstorms over southern WI/Lake Michigan late
tonight and move an eventually weakening complex southeastward.
The majority of solutions take the complex toward IN and OH, with
a minority bringing some of the remaining showers and/or outflow
into the ILX forecast area. This is a low probability outcome at
this point, but may affect heat potential or convective potential
later in the day should it occur.

A heat advisory is in effect for all of central Illinois on
Tuesday as afternoon heat and humidity is likely to result in
heat indices from 105 to 110 degrees. Southwest/west winds
gusting up to 20-25 mph as the pressure gradient becomes oriented
in a more south-north fashion may allow for some mixing down of
drier air and a modest drop in dew points on Tuesday afternoon,
especially west of I-55. However, if this were to happen
temperatures would likely be higher as well with no change
necessary to messaging.

Convective potential for Tuesday afternoon has decreased somewhat
according to the latest CAM data. However, with 1000-3000 J/kg of
MLCAPE east of the deeper mixing, storms which manage to develop
will need to be watched for severe potential. 0-6 km shear is only
around 15 kt which may be a limiting factor, as is the absence of
forcing mechanisms. One notable possibility is the frontal
boundary to the north...if outflow does happen to make it Tuesday
morning, that could increase thunderstorm chances for the
afternoon.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 342 PM CDT Mon Jul 4 2022

Forecast concerns from Tuesday night through Monday include:

1) Longevity and location of impacts from heat/humidity through
the week

2) Watching for periods of greater convective/rainfall potential

The extent of high heat indices on Wednesday is a bit more
uncertain than it is on Tuesday. With the likelihood of early
morning convection and an associated outflow boundary making it
into the ILX forecast area being greater on Wednesday per CAM
solutions, this may play into the northward extent (or lack
thereof) of 105-110 F heat index values. With this forecast, we
did add a few counties in eastern/southeastern IL to Wednesday`s
heat advisory due to confidence being higher in heat continuing
farther south, and in coordination with neighbors. Deterministic
forecasts indicate that chances for somewhat cooler air working
its way southward increase into Thursday and Friday, with NBM
temperature forecasts depicting this well. Our southernmost
counties could hang on to advisory criteria heat for the entire
week, but confidence certainly decreases with time.

Regarding convective and rainfall potential, it does appear more
likely that a weakening cluster of storms will make its way
toward central Illinois on Wednesday morning though the trajectory
and southward extent is still uncertain. Wherever the outflow
boundary ends up may be a factor in where convection initiates on
Wednesday afternoon. Chances are higher (30-50%) Wednesday
relative to Tuesday as plentiful moisture will still be in place.
SPC has a Slight Risk for much of the ILX forecast area on
Wednesday.

Thunderstorm chances continue through the remainder of the week
with the boundary still in the area and a moist, unstable
environment. The current expectation is that rain chances will
decrease by late Saturday into Sunday as the amplitude of the
ridge to the west increases and flow turns more northerly, with
the frontal boundary likely moving southward. Ensemble clustering
shows most solutions (90%) with a trough moving toward the upper
Midwest on Monday driving another frontal boundary and another
chance for showers/storms. The other 10% would move very warm air
back in early next week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 617 PM CDT Mon Jul 4 2022

Cluster of thunderstorms continues to track E/SE into the NE KILX
CWA early this evening: however, the convection will remain
northeast of KCMI. Winds are currently southerly with gusts to
around 20kt at all terminals, but these will decrease to 10kt or
less after dark. Winds will gradually veer to SW overnight, then
to W/SW during the day Tuesday. While convective evolution is
still somewhat uncertain for Tuesday, model consensus suggests
most of the activity will remain well N/NE of central Illinois.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 11 PM CDT Wednesday for ILZ040-047-049>052-
061-066-071-072.

Heat Advisory from noon Tuesday to 11 PM CDT Wednesday for
ILZ054>057-062-063-067-068-073.

Heat Advisory from noon to 9 PM CDT Tuesday for ILZ027>031-
036>038-041>046-048-053.

&&

$$

SYNOPSIS...Barnes
SHORT TERM...AAT
LONG TERM...AAT
AVIATION...Barnes


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