680
FXUS63 KLOT 080259
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
959 PM CDT Fri Jun 7 2024

.KEY MESSAGES...

- Tomorrow will be marked by isolated to scattered rain showers.
  A repeat of the washout last Saturday is not expected.

- Pleasant conditions are expected Sunday through the middle of
  next week with limited (15% or lower) chances for rain and
  seasonable temperatures.

- A shift toward warmer temperatures and higher humidity
  appears on track to arrive after the 2nd week of June.

&&

.UPDATE...
Issued at 959 PM CDT Fri Jun 7 2024

Incoming evening guidance suggests there may be an increasing
chance for a few thunderstorms tomorrow towards midday and into
the afternoon. While the severe weather threat remains low,
trends have been towards perhaps a bit more availability of
surface-based instability, particularly south of I-80 during
the afternoon, although the magnitude of instability will
depend on morning cloud cover/shower activity.

The initiating wave of interest appears to be embedded within a
zone of strong shear vorticity currently dropping south across
North Dakota late this evening. At the surface, a meso
low/troughing across South Dakota is forecast to scoot eastward
overnight and will be crossing the Mississippi River towards
midday tomorrow. While lapse rates are not steep upstairs, just
enough surface moisture may surge northward to carve out a
sliver of MLCAPE during the afternoon to the south of a surging
cold front. Noting a pretty big difference in both surface
dewpoints and air temperatures in the latest guidance, which
seems to explain the disparity in modeled CAPE. However, with it
not currently looking like morning showers and cloud cover will
be overly expansive, there seems to be a window for a theta-e
axis to build into parts of the area, mainly south of I-80 and
east of about I-55 during peak heating. With pretty impressively
veering surface-500 mb flow, deep (and low) layer shear doesn`t
appear to be lacking. Lots of "ifs" in this scenario, but looks
like we can`t entirely throw out the idea of a few more
organized stronger to potentially severe storms developing in
the aforementioned region tomorrow afternoon.

Otherwise, no big changes needed to the overnight grids.

Carlaw

&&

.DISCUSSION...
Issued at 219 PM CDT Fri Jun 7 2024

Through Saturday night:

National satellite fields augmented by RAP-analyzed pressure fields
indicate a decaying low pressure system in central Ontario and an
expanding high pressure system across the middle United States
beneath broad upper-level northwesterly flow. A pair of upper-level
shortwaves are evident, first over the central Plains and the second
near the Montana and Saskatchewan border. Meanwhile, closer to home,
our area is being treated to a delightful early June day with mostly
sunny skies, a northwesterly breeze, low humidity levels, and
temperatures in the mid to upper 70s.

Tonight, upper-level clouds will increase in advance of the leading
shortwave in the Plains. Initial thunderstorms now developing in
central Kansas are poised to grow upscale into a loosely organized
convective system overnight, which will likely move along the
instability gradient well to our southwest across Missouri.
Meanwhile, a few showers may attempt to develop near the
Mississippi River after sunset associated with ephemeral
filaments of frontogenesis. A residual dry
low-level airmass will be eager to chew up initial raindrops
throughout the night, so we will continue a dry forecast. A
passing surface pressure ridge will encourage winds to become
nearly calm overnight. Lows will range from the upper 50s to
lower 60s.

Chances for isolated showers will begin to tick upward toward and
after daybreak Saturday as weak WAA approach from the west
ahead of the secondary upper-level shortwave. The continued dry
airmass may continue to prove hostile for raindrops to survive
to the surface through the morning, but felt advertising
gradually increasing PoPs toward 20 to 30% by noon was a good
idea. A slightly better push of WAA during the afternoon (and
corresponding lowering cloud bases) should be enough to support
a few areas of scattered showers through the evening hours.
Overall, limited moisture and scant instability should limit the
coverage and intensity of showers and curtail more than an
isolated rumble of thunder. (In other words, tomorrow should not
be a repeat washout like last Saturday). Overcast skies will
limit highs to the low to mid 70s.

Tomorrow night, a weak cold front will slip through the area causing
southwesterly winds to turn northwesterly. Lows will dip to the low
to mid 50s.

Borchardt

Sunday through Friday:

We are entering what looks to be a pretty quiet period through next
week. High pressure will begin building into the area on Sunday
bringing sunny skies and temperatures in the mid-to-upper 70s.
Strong northerly flow will cause temperatures to be cooler Monday
and Monday night with highs in the upper 60s and low 70s and lows
potentially dipping below 50 degrees. However, temperatures
will rebound over the following days.

On Monday, a shortwave is expected to propagate through the backside
of the trough that will be pushing off to the east, however, a very
dry moisture profile should inhibit any precipitation from forming.
The next potential for precipitation comes Wednesday as a low tracks
through Canada with a cold front draped to its south. However, model
guidance is not in good agreement about the progression of the upper-
level shortwave/low, so PoPs remain low (15% and below).

A signal continues to be present in long range ensemble guidance for
a pattern shift to warmer temperatures by the end of the forecast
period. Temperatures look poised to push into the upper 80s and
perhaps even lower 90s by the end of the work week.

Carothers

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 653 PM CDT Fri Jun 7 2024

Key Messages:

- Rain showers at times tomorrow

- MVFR ceilings possible tomorrow afternoon

A pair of disturbances traveling through the region will bring
rain showers into the area tomorrow. Light showers may be
observed as early as the morning, but the better chances look to
hold off until the afternoon hours. During the afternoon, MVFR
ceilings may accompany the showers, and some sub-VFR visibility
reductions will be possible beneath the steadiest rainfall rates
as well. An isolated thunderstorm also couldn`t be ruled out,
though it appears that most of the nearby instability should
remain south of the terminals.

Winds will be light and variable tonight with high pressure in
the region before they become southerly and trend southwesterly
with time during the daytime tomorrow. The passage of a cold
front will then shift winds to a more northerly direction late
tomorrow afternoon or evening, with rain chances ending and low
clouds likely to scatter out behind it.

Ogorek

&&

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

&&

$$

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