208
FXUS63 KLOT 032009
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
309 PM CDT Mon Jun 3 2024

.KEY MESSAGES...

- Isolated showers and storms across northern Illinois into
  this evening.

- Unsettled weather pattern continues through mid-week as
  showers and storms are expected Tuesday into Wednesday
  morning.

- Warm, moist air continues to bring the warmer temperatures
  across northern Illinois Tuesday, but cooler temperatures are
  expected Thursday and Friday behind frontal passage.

&&

.DISCUSSION...
Issued at 309 PM CDT Mon Jun 3 2024

Showers and storms have developed this afternoon across
northwestern Illinois, as a north-south oriented boundary sits
along the mid and upper Mississippi River Valley. Additional
development is expected to occur this afternoon through the
evening, however it is expected to remain near and west of the
I-39 corridor over the next hour or 2, before beginning to
shift ne across northern counties of the LOT CWA...north of
roughly the I-88 corridor and then I-90 corridor heading into
the overnight. Isolated strong to severe storms are possible,
however most of the activity is forecast to remain general
showers and storms.

Heading into the overnight and Tuesday, a low pressure system
will deepen across the southern Plains before moving into the
Ohio River Valley late Tuesday into early Wednesday. This will
lift moisture from the Gulf into the area Tuesday morning into
the afternoon, bringing another chance for shower and storm
development as instability once again increases across the
Midwest. With warm southerly air flowing into the region ahead
of this system, expecting showers and storms to rapidly develop
Tuesday afternoon (20-22z) and track eastward through evening. A
larger upper-level low pressure core situated across central
Canada will track eastward Tuesday, trailing an elongated
frontal boundary into the central Plains and deep south. As this
boundary tracks to the east Tuesday night into Wednesday
morning, the chance for a second round of showers and storms
will move through the region. The question at hand today was
timing of this frontal system, as well as the early convection
Tuesday afternoon, this is expected to keep the potential of
strong to severe storms at bay overnight Tuesday into Wednesday.

Drier weather is forecast to return across the Midwest, as the
unsettled weather pattern is finally shifted out of the region
during Wednesday. Along with the dry weather arriving Thursday
and Friday, models are indicating a break in the summer-like
temperatures with highs back in the 70s. The 70s then look to
linger into and through the upcoming weekend across much of the
area, with some cooler temperatures expected near and along the
lakeshore. Chances this weekend for isolated to scattered
showers and storms at times could be possible this weekend,
however the overall probability remains less than 25% at this
time.

Baker

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1242 PM CDT Mon Jun 3 2024

Key Aviation Impacts for the current TAF period:

- Non-zero thunder chances tonight, but confidence was low
  enough to remove from the TAF

- Winds are expected to be prevailing 190, but occasional
  flopping to 170 is possible through Tuesday late morning

- Leading showers may arrive at Chicago terminals late Tuesday
  afternoon

Winds are slowly becoming more prevailing southwesterly;
however, some flip flopping to southeasterly is still possible
through the early afternoon. While there are storms just north
of KRFD moving to the northeast at the time this discussion was
published, the biggest change to the forecast was removing
thunder from the TAFs. There will still be enough instability to
generate a pop-up storm or two later today, latest guidance
keeps the best areas for storms well north of terminals. With
the probability less than 30 percent, it was decided to pull the
thunder from the TAF and monitor chances through the night.

There is low confidence in the exact wind direction overnight
(SE vs. SW), though gusts are expected to come down before
returning Tuesday afternoon. The next system that will bring
showers and storms to the region will likely arrive after 00Z
(and therefore outside the current TAF window). However, latest
high-res guidance suggests a weak boundary drifting northward in
the afternoon. Instability does not look impressive to add thunder,
and while timing may be pushed back in later TAF packages, felt
comfortable introducing -SHRA into the ORD/MDW TAFs.

DK

&&

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

&&

$$

Visit us at weather.gov/chicago