360
FXUS63 KLOT 091939
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
239 PM CDT Thu May 9 2024

.KEY MESSAGES...

- Period of quiet and warmer weather on Friday, followed by
  another chance of showers Friday night.

- Periods of showers and possibly some thunderstorms early next
  week.

&&

.DISCUSSION...
Issued at 239 PM CDT Thu May 9 2024

Through Friday night:

After our break in rainfall, our next batch of showers continues
to quickly shift/develop eastward into the area early this
afternoon in association with the next mid-level impulse now
shifting into northwestern IL. These showers will persist across
much of the area through the remainder of the afternoon before
gradually tapering off from northwest to southeast across the area
this evening. While the thunder threat with this activity will
remain low, we cannot rule out a few storms across our far
southern counties in central IL and IN late this afternoon. Either
way, no severe weather is expected.

Drier weather is expected during the day Friday as we await our
next weather maker shifting southward across the Upper Midwest.
Partly cloudy/sunny afternoon skies will allow inland temperatures
to rebound back into the mid to upper 60s. However, conditions
look to become favorable to allow an afternoon lake breeze to
develop along the northeastern IL shores. While the lake breeze
may not move more than 10 to 15 miles inland prior to sunset,
onshore easterly winds will keep conditions a few degrees cooler
along the lakeshore Friday afternoon.

Our next chance of rain will come Friday night as the next fast
moving and compact impulse digs southeastward across the western
Great Lakes. This looks to be a quick hit (2 to 4 hours) of
mainly some showery activity with an approaching surface cold
front, though steepening lapse rates could also support a couple
of embedded thunderstorms. The quick movement of the precipitation
should keep total amounts rather low, so we really do not look to
have any major hydro threats with this activity.

KJB


Saturday through Thursday:

The rain chances forecast for Friday night will clear the area by
daybreak Saturday. Surface high pressure building in from the south
and steady height rises aloft will then bring pleasant Spring
conditions to the area for the weekend. Temperatures will be rather
seasonable on Saturday with highs forecast in the middle and upper
60s, lower 60s closer to the lakeshore. A tight pressure gradient
behind the departing storm system will bring breezy NW winds to the
area on Saturday. As the surface high moves across the Tennessee
Valley Saturday night into Sunday, the mild return flow will pull
highs into the middle and upper 70s to close out the weekend, again
with a hefty breeze expected during the day.

An upper trough looks to move across the central Plains and lower
Midwest Monday into Tuesday. The surface response will be a low
pressure center that medium-range guidance can agree will pass to
our south. Nonetheless, broad upper forcing in a moisture-rich
profile will lead to rain chances across our domain early next
week along the storm`s northern flank. An ample amount of MUCAPE
north of the low could bring us some elevated thunderstorms as
well, although heavy rain may be the most appreciable concern. This
wave will hang out in the region through Tuesday with another wave
moving in right behind for midweek ushering in what could be a
somewhat active week ahead with lots of room for rain chances.
Luckily, nothing overly impactful appears on the scope through the
middle of next week.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1248 PM CDT Thu May 9 2024

Key Messages:

- Another period of showers expected this afternoon.

- Predominately MVFR CIGs into this evening, with a 30-50%
  chance for a period of IFR CIGs at the Chicago area terminals
  late tonight.

- Lake breeze expected Friday afternoon, though confidence is
  low with it making it to ORD late in the day.

While the rain early morning rain has moved out of the area,
another batch of rain is already developing eastward into
northwestern IL in association with the next mid-level
disturbance. Expect this area of showers to overspread the
Chicago area terminals after 19-20z, with periods of showers
expected through the remainder of the day before the activity
ends into early this evening (00-01z).

MVFR CIGS will also persist the remainder of the day, but may
improve a bit as the rain onsets this afternoon. CIG trends into
tonight then remains a bit unclear. While a period of improving
conditions is possible for a period mid to late this evening,
the potential then exists for CIGs to trend back down again
overnight into very early Friday morning, especially near the
lake. As such, some terminals near Lake Michigan could
experience a period of IFR CIGs after 09-10z tonight through
early to mid morning on Friday. Confidence is not high with this
period of low CIGs, but we have opted to hint at the opportunity
with a few hour tempo mention for IFR CIGs in the latest TAF
iteration. Any low CIGs will quickly improve through the mid
morning hours of Friday.

Wind trends also look to become tricky Friday afternoon as a
lake breeze develops across far northeastern IL. It remains
unclear as to how far this lake breeze will be able to make it
through the afternoon, which makes a deterministic wind
forecast, particularly at ORD, quiet difficult. If the lake
breeze remains just east of the terminal, winds at ORD would
likely trend to a west-northwesterly direction Friday afternoon,
while areas just east of the boundary turn easterly. At this
time, I have opted to only mention an eastward wind shift at
MDW, where confidence is slightly higher.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 3 AM CDT Friday for the IL and IN
     nearshore waters.

&&

$$

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