Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 301109

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
609 AM CDT Fri Jul 30 2021

213 AM CDT

Through Saturday...

Morning surface analyses depict a building high pressure system over
the northern Plains, departing low pressure system off the Atlantic
Seaboard, and stationary front draped across the Ohio River Valley.
Upstairs, northwesterly flow prevails over the Great Lakes thanks to
deep ridging in place across the central United States. Locally,
current temperatures are comfortable and in the mid 60s with dew
points in the upper 50s to lower 60s.

Today, filtered sunshine and stout flow off Lake Michigan will lead
to cooler temperatures compared to the past week with highs in the
low to mid 70s -- coolest along the lakeshore. While
northeasterly winds off Lake Michigan will gradually abate as the
day progresses, waves will remain choppy and supportive of
dangerous rip currents through this evening. (Stay dry when waves
are high!) Tonight, winds will become light and variable as the
aforementioned surface high pressure slides over the Great Lakes.
Toward daybreak, showers and thunderstorms are expected to ride
along the stationary front draped across central Missouri and
Illinois, with the most likely scenario being our entire area
remains dry.

Saturday will be a smidge warmer than today with highs in the upper
70s to lower 80s, warmest along the IL/WI state line where cloud
cover will be thinnest. Smoke from wildfires across the west will
become increasingly thicker by Saturday afternoon, and may even
extend toward the ground in the form of haze as suggested by recent
iterations of the HRRR. Although low-level moisture will slowly
increase as the day progresses, modest low-level capping (not to
mention filtered sunshine due to clouds and smoke) favors a dry
forecast through the daylight hours.



247 AM CDT

Saturday night through Thursday...

A cooler and much less humid weather pattern is shaping up for
much of the extended period as a persistent long wave trough sets
up over the eastern half of the country, downstream of a
persistent upper ridge over the western CONUS. Within this larger
scale pattern, several smaller scale disturbances are likely to
track southward across the Midwest and western Great Lakes region
late in the weekend and into next week. The first of these looks
to drive another surface cold front southward across the area
Saturday night. While the area will see a reinforcing shot of
cool, less humid air for Sunday in the wake of this front, we may
also experience a period of showers, and perhaps a few storms
Saturday night as the front moves into the area. For this reason,
we continue to mention chances POPs during this period.

High temperatures are only expected to top out in the 70s Sunday
as northerly winds in the wake of Saturday nights cold front
continue to usher in this cool airmass. We will have to keep an
eye on the strength of these northerly winds over Lake Michigan
into Sunday, as they could result in another day of high waves and
dangerous swimming conditions at the area beaches for Sunday.

Cooler than average weather looks to continue through at least
early next week. Thereafter, we do look to slowly moderate
temperatures back to around normal (mid 80s). Precipitation
chances after Sunday look low across the area, and outside of any
isolated diurnal showers, I think most areas will stay dry. The
current blended forecast does keep the area void of mentionable
precipitation until Friday, which seems reasonable.



For the 12Z TAFs...

There are no significant weather concerns expected through the
period as an area of surface high pressure builds southward
overhead during the day. VFR conditions are expected, but some
increasing higher level cloudiness from the northwest may result
in CIGs above 12000 feet this afternoon and evening. Otherwise,
expect a predominately east-northeasterly wind up around 10 kt
through the day, before becoming light and variable tonight and
then west-southwesterly into early Saturday morning.



IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104 until 7 PM Friday.

IN...Beach Hazards Statement...INZ001-INZ002 until 7 PM Friday.

LM...Small Craft Advisory...nearshore waters
     until 7 PM Friday.



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