014
FXUS63 KLOT 100538
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1238 AM CDT Fri May 10 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 /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1238 AM CDT Fri May 10 2024

Aviation Key Messages:

* Light northwesterly winds (around 5kt) this morning will back
  westerly and increase in magnitude (to 10-12kt)  this
  afternoon.

* VFR clouds based near 10kft this morning will transition to
  VFR cumulus based near 5kft early this afternoon.

* A band of showers with northwesterly wind gusts as high as
  30kt will swing through the terminals this evening (generally
  between 03-06Z).

Discussion:

The "widening" of the surface pressure gradient across the
western Great Lakes along far eastern influence of a surface
high diving into the Plains will allow for northwesterly winds
at press time to continue backing westerly by early afternoon.
Sustained speeds of 10-12kt this afternoon may be accompanied
by a few gusts of 15-20 kt, though opted to withhold mention of
gusts for brevity and the expectation for limited impacts to
aviators.

Broken mid-level clouds based near 10kft between two upper-
level troughs early this morning should scatter by mid-morning,
setting the stage for the development of a healthy cumulus
field based near 5kft this afternoon. With forecast soundings
showing appreciable depth and instability within the cumulus
layer, a stray shower or two cannot be ruled out particularly
between 20 and 00Z. For now, will withhold any formal mention
of showers this afternoon in the outgoing TAF package given the
expectation for a relatively limited coverage (not to mention
the probability of occurrence being less than 20%).

A vigorous upper-level shortwave and associated cold front will
race southeastward across the Great Lakes this evening
accompanied by a strongly forced band of showers. Chances for
thunder appear to be less than 10% at the terminals owing to a
loss of diurnal instability, though thunder may be observed
earlier in the day further to the north in Wisconsin. With a
pocket of dry air expected to be in place beneath cloud bases
this evening, the band of showers may produce gusty
northwesterly winds perhaps as high as 30 to 35 kt in spite of
the development of a shallow near-surface stable layer. For
this reason, opted to introduce targeted TEMPO groups for
showers with northwesterly wind gusts to 30 kt at all terminals
generally between 03-06Z (except GYY, as the showers are
expected to arrive right 06Z). A few showers may continue behind
the front as mid-level lapse rates steepen within the core of
the passing upper-level wave.

Borchardt

&&

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

&&

$$

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