Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 061920

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
220 PM CDT Wed Jul 6 2022

Issued at 214 PM CDT Wed Jul 6 2022

Through Thursday night...

Rain and thunderstorm chances continue to be the main focus of the
forecast through tomorrow night. High pressure is in place over
Lake Superior with a surface stationary boundary in vicinity of
the far southern part of the forecast area. Surface low pressure
is over southern Kansas, though a weaker, convectively induced low
is tracking east across southeast Iowa. This Iowa circulation
will continue eastward and probably drift a bit east-southeast
along the frontal boundary this evening. Some shower/thunder
activity continues with it and latest RAP analysis does indicate
some instability. Still have several hours before the circulation
reaches Livingston/Ford Counties and will continue with slight
chance pops as the precip associated with it is expected to wane
as instability decreases toward sunset.

Several subtle shortwaves appear on water vapor imagery emanating
from the southern high plains and will likely produce new
convection tonight with one area expected across central and
eastern Nebraska and a second trailing it to the west. The first
round is expected to track eastward across southern Iowa and
probably focus along and south of the stationary front which is
expected to remain just south of the forecast area. We should see
some scattered rain north of the front which will move into the
forecast area Thursday afternoon. Coverage should be highest west
by late afternoon. Instability looks minimal so thunder chances
will be low as well. The second wave looks better organized and
will come with better overall synoptic support as surface low
pressure will track from Kansas to central Illinois into Friday.
This will bring a combination of ascent from a low level jet
nosing into central Illinois and right entrance region of an upper
jet which will also increase precipitable water to work with (from
1.5 inches north to 2.25 inches south) Thursday evening and
Thursday night. This should result in a more substantial chance
for rain and some thunderstorms to cross the area. At this point,
highest rainfall amounts would be across the southern part of the
forecast area closer to the front, stronger low level forcing and
higher available moisture. Will need to continue to refine focus
area for any heavy rain/flooding potential as the track of the
system comes into better focus into tomorrow.



Issued at 218 PM CDT Wed Jul 6 2022

Friday through Wednesday...

We`ll continue to transition out of our more active stretch on
Friday, but will have to kick one last disturbance east before we
return to completely dry conditions across the region. Rain should
be ongoing Friday morning, although it`s still a bit unclear just
how far north this activity will be with guidance today still
trying to settle in on a preferred path to this last vort max.
Either way, while atmospheric moisture will be high with PWATs
still near or just north of 2 inches, instability looks pretty
muted given marginal lapse rates suggestive of an embedded thunder
potential staying relegated to areas south of I-80. While guidance
appears to have slowed just a bit pushing the last waves of ascent
out of our region on Friday, it`s still looking like we`ll manage
generally precipitation-free conditions north of I-80 by early
Friday afternoon, with the last chances finally pushing south of
the area entirely by early evening.

North to northeast flow will prevail Friday and Saturday as high
pressure builds across the Great Lakes region which will
effectively hold lake-adjacent highs in the mid 70s. Flow will
veer to the south and southwest through Sunday, but the gradient
flow remains weak suggesting a lake breeze will still manage to
develop in the afternoon.

Boundary layer moisture is progged to increase quickly on Monday,
with upper 60s/low 70s dewpoints sloshing east out of Iowa. Medium
range guidance is in reasonable agreement depicting a fairly
robust shortwave translating across the UP of Michigan Monday
afternoon and evening. Commensurate increases in the mid and
upper-tropospheric flow, combined with building instability
suggests an increased shower and thunderstorm threat ahead of an
attendant cold front.

Broad cyclonic upper flow is forecast to develop through the end
of next week which should help cool things off in the wake of a
Monday night cold frontal passage. Looks like a few shots at
additional isolated shower activity during this time frame.



For the 18Z TAFs...

Forecast concerns for the terminals...
*Low clouds continue to scatter out this afternoon

*Chance of showers Thursday evening

An area of low MVFR clouds continue to push through the area this
afternoon in the wake of this morning`s showers, but signs of
improvement are being seen across northern Illinois and southern
Wisconsin. These lower clouds are expected to continue to scatter
out through the afternoon which will leave VFR clouds moving
across the area for the rest of the TAF period. Winds this
afternoon will maintain their northeasterly direction with speeds
generally around 10 kts with occasional gusts into the teens this
afternoon. Once the gusts ease this evening, winds will gradually
become more easterly through the night and then southeasterly
Thursday morning with speeds remaining around 5 to 10 kts.

Another upper-level wave will begin to move into northeastern
Illinois Thursday afternoon which will bring additional chances
for showers to the terminals. Guidance continues to vary in the
exact timing the showers will arrive, but the best time looks to
be after 22z Thursday at the Chicago sites. Instability looks to
be very marginal Thursday afternoon which leads me to believe that
any precipitation at the terminals would be in the form of
showers, however; a stray lightning strike can not be completely
ruled out at this time. For now I have introduced a PROB30 for
SHRA at the 30 hour TAF sites for this potential with rain likely
to be added to the other sites in future forecasts.





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