Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 250747
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
247 AM CDT Mon May 25 2020

.SHORT TERM...
247 AM CDT

Through Tuesday...

An earlier mass of convection which tracked out of central
Illinois Sunday evening continues to slowly fizzle early this
morning as it encounters somewhat drier low-mid levels as
evidenced by recent AMDAR and point forecast soundings. Radar
loops depict a clear remnant cyclonic twist with this feature, but
the attendant mid-level vort max looks to lift out of our area
through daybreak. From a conceptual model standpoint, this would
likely leave behind at least some degree of mesoscale subsidence
in its wake. As a result, there`s a bit of uncertainty with the
PoP forecast for today as various global and high-resolution
guidance squeeze out somewhat more widespread precipitation
coverage than we`d anticipate given this and a lack of more
coherent surface boundaries to force convection. While it will
undoubtedly be quite unstable this afternoon with upper 60s
dewpoints and mid 80s air temperature prevalent, the main
shortwave of note looks to remain well west across Kansas and
Missouri. With this in mind, have elected to cap PoPs at 30% area-
wide today. Any storms that do develop would certainly be capable
of producing gusty winds and brief heavy rainfall, however.

Anticipate that any convection which develops potentially into a
loosely-organized complex into western Iowa and Missouri this
afternoon and evening will diurnally wane with the loss of heating
tonight.

Tuesday should feature some additional southerly breezes as we
pick up just a bit more flow in the low-levels, especially the
farther west you go. Once again, while afternoon instability will
grow, in the absence of any more coherent surface boundaries,
there really doesn`t seem to be much to result in organized
convection. Several additional shortwaves will drift northward
across the plains during this time, but these look to remain a bit
too far to our west to result in much increase in large scale
forcing. Chance PoPs once again seem reasonable for Tuesday as a
result.

Carlaw

&&

.LONG TERM...
307 PM CDT

Tuesday through Saturday...

Warm and humid conditions with a threat for thunderstorms at times
will continue to be the weather story through Thursday. Thereafter,
we look to transition to a drier and more pleasant weather pattern
for Friday into next weekend. Similar to Mondays weather,
thunderstorms will be possible over the area due to weak/no
capping, but the lack of a clear forcing mechanism should curtail
the threat of more widespread coverage. There is a bit better
signal for the potential for more numerous thunderstorm coverage
late Wednesday and Thursday. A surface cold front is forecast to
approach the area during this period, and may thus act as a better
focus for storm development. The threat of severe thunderstorms
continues to look low across the area, due to a weakly sheared
environment.

Looking ahead to Friday and at least the start of next weekend,
there will be a temporary pattern change thanks to a deep upper
trough passing across Canada that will knock down height and
thermal fields. Expansive high pressure settling southward behind
Thursday`s cold front passage will provide a cooler and much
drier/less humid air mass with dew points in the 40s and 50s after
several days in the 60s to lower 70s. High temperatures should
top out into the 70s inland Friday and Saturday unless temps aloft
trend lower, with cooler low-mid 60s lakeside. Depending on the
strength of the north-northeast winds on Friday, there may be a
threat for elevated waves creating strong currents and dangerous
swimming conditions at some beaches.

Castro/KJB

&&

.AVIATION...
For the 06Z TAFs...
1238 AM CDT

The concerns include:

* SHRA and embedded TSRA likely moving into the terminals early
  this morning with a couple hours of on station TS possible
* Isolated to widely scattered TSRA possible later today with low
  confidence
* Gusts of 15-20 kt possible this afternoon from a south-
  southwesterly direction (190-210 deg)

The main item of note in the near term is the area of SHRA/TSRA
over central Illinois associated with a northward lifting
disturbance. While there`s a chance it does weaken and erode prior
to reaching the terminals, think that it will hold together long
enough to bring a period of SHRA to the Chicago area terminals
early this morning. TS occurrence is a bit more questionable, but
opted for a short 2-hour TEMPO TSRA mention with the leading edge
of the activity (including MVFR conditions). Will monitor trends
and adjust as needed.

It`s unclear what sort of effects this early morning activity
will have on convective chances the rest of the day. Moderate
instability will redevelop, but a source of lift for higher
coverage of thunderstorms is expected to be lacking, which keeps
confidence too low for additional mention of any on station or
vicinity SHRA/TSRA. South- southwest winds may gust up to the
15-20 kt range this afternoon. Lighter southerly winds are then
expected Monday night. Can`t rule out SHRA/TSRA over the region,
but confidence remains low.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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