Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 171957

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
257 PM CDT Mon Jul 17 2017

215 PM CDT

Through Tomorrow...

With high pressure centered over lower Michigan and a ridge axis
extending southwest through the middle Mississippi Valley,
conditions will remain unseasonably cool and dry through the night
tonight with temperatures topping out in the upper 70s to around
80 F. With dewpoints in the middle to upper 50s, mostly clear
skies and light winds, lows tonight should range from the middle
to upper 50s over much of the area to the middle 60s in downtown
Chicago. Temperatures and dewpoints will be on the rise tomorrow
as the high shifts to the east and low level swly flow sets up a
return flow of moisture. Dewpoints should rebound back into the
middle 60s. The pressure gradient will remain relatively weak
across the region tomorrow, so lake breeze development is likely.
This should keep lakefront locations in the middle to upper 70s,
while inland locations should see more seasonable temperatures as
highs reach into the middle to upper 80s. No pcpn is expected
through tomorrow as upper ridging remains over the region. A
strong shortwave is expected to cross through the upper
Mississippi Valley tomorrow, but any impacts will not be until at
least tomorrow night.


242 PM CDT

Tuesday night through Monday...

Coming shortly.


For the 18Z TAFs...

No significant concerns for the terminals for the period. With
high pressure over the region, skies will remain mostly clear with
no obstructions to visibility. With the center of high pressure
over the upper Great Lakes, winds will will be nely through the
remainder of the day and then becm lgt/vrbl overnight. For
tomorrow, the high will move very little, leaving a weak pressure
gradient over the region. Expect that lgt/vrbl winds should
persist into early afternoon and then a lake breeze should
develop, turning winds to ely at ORD/MDW and nly at GYY with
speeds up to 10 kt briefly following the lake breeze passage.
Winds at DPA/RFD should be more swly at 5-7 kt which is more
reflective of the large scale pattern.


242 PM CDT

Our sympathies go to the Mack racers who are strung out from
the Manitou Islands into the straits with very little wind this
afternoon, in sharp contrast to the conditions they fought most
of Sunday. It appears that some of them are starting to manage 3-5
knots, and while local thermal effects will most likely dominate
through this evening, the overall gradient appears to be
strengthening and offering hope for a finish tonight or early
tomorrow for most participants. Moderate south to southwesterly
flow develops across the lake Tuesday and continues to increase
into late Tuesday evening, though wave growth does not get out of
hand, peaking at 3 to 5 ft or maybe a bit higher in the open
waters toward the north end. A front dropping down the lake early
Wednesday turns winds north again and eventually relaxes the
gradient by Wednesday afternoon.






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