Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241842

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
142 PM CDT Mon Jul 24 2017


Through Tuesday...

142 pm...Stratocu is expected to scatter out and dissipate later
this afternoon into this evening but confidence on timing/trends
is low as even the back edge of the clouds over southern Lake
Michigan have shown redevelopment recently. Its possible mostly
cloudy skies continue into the evening with scattering tonight.
There had been some potential for patchy fog tonight and there
still is but confidence is low with the expected slower clouds
scattering out. So no mention of fog with this forecast and trends
will need to be monitored this evening.

High pressure will build across the Great lakes region tonight
and begin shifting east on Tuesday. Light winds overnight will
turn southeast Tuesday morning and a lake breeze is expected by
afternoon keeping the lake shore a few degrees cooler. Low
confidence regarding how far inland this lake breeze may move.
Highs inland likely to reach the lower 80s. cms


343 AM CDT

Wednesday through Saturday...

Warm and humid weather conditions return briefly Wednesday into
early Thursday, with attendant thunderstorm potential. Mainly dry
weather is expected late in the week, as medium-range guidance
depicts an expansive area of surface high pressure developing
across the region Friday into Saturday.

A vigorous mid-level short wave is expected to propagate across
the northern Great Lakes Wednesday, with it`s associated surface
low pressure center tracking across Ontario and a cold front
trailing into the local area Wednesday night. Low-level winds turn
southerly ahead of the front Wednesday, resulting in return
moisture feed into the region. Forecast soundings generally depict
a capped profile during the day, with the greatest potential for
thunderstorm development expected to be focused along/ahead of the
approaching cold front Wednesday night. Deep layer 0-6 km bulk
shear increases to 30-40 kts, with PW`s increasing to 2.50 inches
per GFS, suggesting the potential for organized strong/severe
storms and heavy rainfall threat overnight. Thunderstorm/heavy
rainfall threat continues Thursday morning, and possibly into
early afternoon across the south/southeast, as the front slowly
sags southeastward across the remainder of the forecast area.

Amplifying upper trough then moves east of the area Thursday
night, with broad ridging developing aloft across much of the
central CONUS states. Surface high pressure spreads across the
Upper Midwest and Great Lakes region into Saturday, setting the
stage for a return of drier and slightly cooler weather for the
end of the period.



For the 18Z TAFs...

1229 pm...Northeast winds 10-15kt will continue into this evening
and gradually diminish as high pressure moves toward the region.
Winds will turn light southeasterly Tuesday morning and should
remain southeast or southerly for much of the day with speeds
increasing toward 10kts. A lake breeze is expected Tuesday
afternoon but fairly low confidence regarding how far inland it
may move.

Bkn/ovc 3-4kft stratocu deck has been slow to show signs of
scattering out though the back edge continues to make progress
across southern Lake Michigan. Still expect clouds to scatter
mid/late this afternoon...first near the lake...but confidence is
decreasing as to when this will occur and its possible clouds
remain into this evening southwest of the terminals.

Patchy fog is possible tonight...mostly likely in the usual spots
but confidence is low especially with the lower confidence for
how fast clouds will scatter out this afternoon. Best chance of
fog would likely be at rfd/dpa but no mention with this forecast.



142 pm...High pressure will build across Lake Michigan tonight
and then shift east to New England Tuesday night. Northerly winds
will slowly diminish this evening then shift southerly Tuesday
morning. An area of low pressure will move across Hudson Bay
Tuesday night with a trailing cold front into the upper midwest.
The gradient will likely tighten ahead of this front with a period
of 15-25kts Tuesday night into Wednesday. A second low will move
across the southern part of the lake Wednesday night into Thursday
morning. Winds will shift northerly behind this low and a period
of 30kts is possible Thursday afternoon into Thursday night...
though there remains some uncertainty on timing and strength of
the low. cms


IL...Beach Hazards Statement...ILZ006-ILZ014 until 10 PM Monday.

IN...Beach Hazards Statement...INZ001-INZ002 until 10 PM Monday.

LM...Small Craft Advisory...nearshore waters until 10 PM Monday.




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