938
FXUS63 KLOT 280205
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
905 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- Quiet conditions will persist into the overnight hours.

- A Marginal Risk for severe weather exists Friday over most of
  the area and southeast of Chicagoland on Saturday. While the
  threat isn`t particularly high-end, some gusty winds can`t be
  ruled out with any of the stronger storms.

&&

.UPDATE...
Issued at 905 PM CDT Thu Jun 27 2024

Mid level moisture continues to move in from the west and there
are some weak lobes of vorticity moving in out of ahead of a
shortwave in northwestern Iowa. This has resulted in some
returns developing on radar; however, dew points over
northeastern Illinois remain in the 40s to low 50s and the 00Z
KDVN sounding shows a pretty robust drier layer below 700 mb.
And while there was brief sprinkles reported in Dubuque about an
hour or so ago, the forecast was kept dry through the night.

Winds will be light and remain out of the east, before turning
to the southeast and eventually south late morning. Better warm
air and moisture advection will allow for PoPs to increase
through the morning but will really struggle with the drier air
in place as well as the limited forcing available. As such, the
PoPs were adjusted slightly to account for the eastward movement
of the wave, but were clipped to keep the chance (25 to 45
percent) for showers tomorrow morning west of the Fox Valley,
limiting the Chicago Metro area to only a slight chance. Model
CAPE is better far west of the area and does not start to
encroach into the forecast area until Friday evening at the
earliest, so thunder was kept out of the forecast through much
of Friday.

DK

&&

.DISCUSSION...
Issued at 244 PM CDT Thu Jun 27 2024

Through Friday Night:

Quiet conditions will persist into the overnight hours as a
moderately strong high pressure lingers over Lake
Ontario/Upstate New York. Warm advection will increase over the
Western Corn Belt tonight and isentropic upglide over an
approaching warm front will lead to showery precipitation over
Iowa tonight. Going into tomorrow, this rain will have to fight
some lingering low level dry air from the high pressure system,
but with time, the low levels will saturate and light rain
should spread in from the east and northeast with time, mainly
in the afternoon. CAPE with this activity is projecting to be
weak so widespread thunderstorms are not expected, but a few
rumbles of thunder may move through especially in the late
afternoon/early evening when models project a weak shortwave
moving through. There may be a bit of a lull around midnight,
before more showers and rumbles of thunder occur overnight as a
sfc front approaches from the northwest. There may be a bit
more elevated CAPE along the front. Any strong storms that occur
during this time period may have some gusty winds, but severe
weather chances attached the Marginal Risk look low.

NWS Chicago


Saturday through Thursday:

The sfc cold front is expected to slide southeast with time late
Saturday morning into the afternoon hours. As the front moves
through, dew points and temperatures should ease with time
leading to comfortable and cool conditions Saturday night into
Sunday. Comfortable and seasonable conditions are then expected
Sunday and Monday as high pressure exerts it`s influence over
the Upper Midwest.

An unsettled pattern is then projected to return Tuesday into
the rest of the extended as long-range models depict multiple
shortwaves and bouts of warm advection into late next week,
spurring daily chances for showers and thunderstorms.

NWS Chicago

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 633 PM CDT Thu Jun 27 2024

Key Aviation Messages:

- East winds turn southeast by morning, then become breeze from
  the south-southwest by early Friday afternoon.

- Scattered showers and sprinkles expected in the area by late
  morning/midday, most likely at KRFD with lower coverage
  farther east. TSRA threat appears minimal until later Friday
  night, possibly after midnight.

Surface high pressure over the western Great Lakes will drift
off to the east overnight, allowing east-northeast winds to turn
southeast by morning. Surface winds will then continue to veer
to south-southwest by early afternoon, as an area of low
pressure develops well northwest of the region and moves into
the upper Midwest through Friday evening. South-southwest winds
Friday afternoon will increase a bit in response to the
tightening pressure gradient and some gusts in the 20-25 kt
range are likely especially late. Gusts should ease with sunset,
with winds remaining south during the evening.

Low level air mass is expected to remain fairly dry tonight into
Friday thanks to the retreating surface high, with low level
moisture returning north across the Plains to our west through
the day. Warm/moist advection will develop aloft however, which
should develop a mid-level VFR cloud deck and some high-based
showers or sprinkles by mid-day. Weak mid-level lapse rates and
dry low-levels should keep thunder potential low through the day
however. Low-level moisture eventually edges into the area from
the west and southwest Friday night, ahead of a cold front
which will arrive well after the end of the current TAF period.
TSRA potential increases late Friday evening and more so after
midnight, though various guidance is somewhat divergent with
timing. Included a prob30 for TSRA toward the very end of the
KORD/KMDW 30-hour forecast, though again greater potential may
end up being just beyond the end of this forecast.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 10 PM CDT this evening for
     ILZ103-ILZ104.

IN...Beach Hazards Statement until 10 PM CDT this evening for
     INZ001-INZ002.

LM...None.

&&

$$

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