-- Discussion containing changed information from previous version are highlighted. --
815
FXUS63 KLOT 301126
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
626 AM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Dangerous swimming conditions at area beaches today and
  tonight due to breezy onshore winds and high waves.

- Return to more typical summer temperatures and humidity
  Tuesday onward with periods of showers and thunderstorms too.

&&

.DISCUSSION...
Issued at 336 AM CDT Sun Jun 30 2024

Through Monday:

High pressure will begin to build into the area today in the
wake of last night`s cold front which will establish a period of
seasonably cool temperatures and comfortable humidity through
Monday. Winds will continue to settle into a northerly direction
(northeasterly for those along the IL lakeshore) this morning
and increase in speed with gusts of 20 to 25 mph expected by
this afternoon. As a result, temperatures today will be notably
cooler with highs toping out in the low to mid-70s. Though, the
aforementioned onshore winds will keep temperatures in the mid
to upper 60s for areas near the lake. In addition to the cooler
temperatures, the breeze onshore winds will also build waves at
area beaches resulting in dangerous rip currents and swimming
conditions. So if planning to head to the beach today take heed
of the Beach Hazard Statement in effect and stay out of the
water.

The breezy winds will diminish this evening which will allow
waves to gradually subside overnight. However, winds will remain
onshore into Monday morning which will still support some
hazardous swimming conditions especially for weaker swimmers.
The diminishing winds in addition to the mostly clear skies and
low humidity will also make for a rather chilly night with
temperatures expected to dip into the upper 40s to lower 50s
across the area with more moderate readings in the mid-50s near
the lake. Temperatures will rebound Monday afternoon as winds
turn southerly and climb into the mid to upper 70s inland and
lower 70s near the lake.

Monday Night through Saturday:

The aforementioned surface high will begin to move eastward
Monday night as an upper trough begins to eject into the
northern Plains. Ahead of this trough a narrow plume of higher
moisture and instability is expected to be streaming northward
across the Mississippi Valley which should allow for the
development of showers and thunderstorms across the northern
Plains and upper Midwest. While this area of showers and storms
is forecast to gradually spill over into northern IL (mainly
north of I-88) late Monday night into Tuesday, the cooler and
drier airmass over our area should weaken the showers/storms as
they arrive, at least initially.

However, increasing southerly flow across the area on Tuesday
will replenish the moisture and aid in destabilizing the
atmosphere as temperatures warm Tuesday afternoon. Therefore,
shower and thunderstorm coverage does look to increase across
our area Tuesday afternoon. Though the lack of more organized
synoptic forcing over northern IL and northwest IN should keep
the highest storm coverage north of I-80 and more so near the
IL-WI line.

The aforementioned trough will continue its eastward
propagation across the northern Great Lakes and into Ontario on
Wednesday which will force a cold front through northern IL and
northwest IN. Given that the front is expected move through
Tuesday evening and overnight, the unfavorable diurnal time may
allow for the loss of more robust instability and in turn cause
the showers and storms along the front to gradually weaken with
southward extent. Regardless, the front should exit to our south
sometime late in the day on Wednesday which should offer at
least a few dry hours on Wednesday.

Heading into the July 4th holiday on Thursday, the front is
forecast to gradually lift back northward as a warm front
Wednesday night into the day on Thursday. Depending on how far
north the front gets will determine the extent of shower and
storm coverage during the Thursday into Friday timeframe as
another shortwave trough pivots into the Great Lakes. At this
point, guidance is favoring an afternoon and evening show for
our area on Thursday with the greatest coverage in our southern
CWA. However, this general timing is still low confidence given
that we are still several days out and existing storms on
Wednesday will play a role in frontal placement. Therefore,
those with outdoor plans for the 4th should keep an eye on this
period.

Regardless of how Thursday plays out, it does appear that
another front should push through on Friday and finally bring
the periods of showers and storms to a close heading into next
weekend. Though the typical late June early July heat and
humidity is forecast to remain through the period with highs in
the mid to upper 80s and dew points in the 60s to around 70 each
day.

Yack

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
-- Changed Discussion --
Issued at 625 AM CDT Sun Jun 30 2024

Northerly winds expected today, strongest at the terminals
closer to the lake (ORD, MDW, GYY) where winds should gust over
20kt at times, especially this morning. Winds will diminish this
evening with sunset to light northeast or even calm at times.

Lake effect stratocumulus should continue to stream into GYY
this morning with some tendency for stratocumulus to develop or
spread into Chicago as well. GYY will likely have at least
occasional MVFR CIGS this morning. For ORD and MDW, a brief
period of higher end MVFR CIGS cannot be ruled out, but
generally thinking VFR conditions for ORD and MDW.

- Izzi
-- End Changed Discussion --

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through late tonight for ILZ006-ILZ103-
     ILZ104.

IN...Beach Hazards Statement through late tonight for INZ001-INZ002.

LM...Small Craft Advisory until 4 AM CDT Monday for the IL and IN
     nearshore waters.

&&

$$

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