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FXUS63 KLOT 232322

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
622 PM CDT Fri Jun 23 2017

141 PM CDT

Through Saturday...

KLOT radar getting a breather this afternoon as a cold front has 
pushed showers and storms southeast of the area. Comfortable
dewpoints have fallen considerably, with near 50s north to around
60 south with just a few high clouds, and temperatures in the mid
70s to near 80 makes for a fairly pleasant Friday afternoon. 
Meanwhile aloft, the upper air pattern features a low over James 
Bay, with another low near the Manitoba lakes region. Several 
shortwave disturbances ahead of the latter low will continue in 
the westerly flow across the plains. The first disturbance will 
lead to clouds and some showers upstream this afternoon, but its 
arrival later this afternoon/early evening is not favorable for 
much in northeast IL or northwest IN more than some light showers 
or sprinkles farther west as higher surface pressures will spread 

Expect a quiet night with clearing skies. Winds will hold out of 
the west as the surface high remains well off to our west, and low
pressure will shift east through the Ohio Valley and towards the 
Atlantic. The upper low across Manitoba will spread southeast 
through the upper Midwest on Saturday morning, then to the western
Great Lakes late in the day. Fairly cold air aloft for late June 
will allow some very steep low level lapse rates to set up. Expect
some later morning to early afternoon cumulus development and 
likely some breezy west-northwest winds as the surface pressure 
pattern remains the same and decent mixing will occur due to the 
steep lapse rates. Forecast soundings do depict a bit of an 
inversion around 850 mb or so, which would suggest any showers 
that form that would be isolated, shallow and largely void of 
thunder. Otherwise, seasonally cool temperatures will top off in 
the low to mid 70s, with cool dewpoints dropping into the 40s in 
the afternoon.



259 PM CDT

Saturday night through Friday...

For the longer term forecast period, general trends remain 
consistent with previous runs and the short term forecast period 

By Saturday night, the longwave pattern will continue to trend to a 
high amplitude, low wavelength, slowly progressive longwave pattern. 
broad upper troughing east of the Rockies and strong upper ridging 
over the west coast.  The general trend through the weekend and into 
early next week will be for well below normal temperatures and low 
precipitation chances.  A series of weak shortwaves will drop 
through the nwly flow aloft helping to deepen the upper trough 
Sunday and Monday and max temperatures will be the lowest of the 
period with highs only in the lower 70s.  It is possible that some 
locations may only reach the upper 60s.  Highs in the upper 60s to 
lower 70s would be 10 to 15 degrees below seasonal normals, which 
are in the lower 80s for late June.  With Broad cyclonic flow aloft 
persisting across the region through early next week, there will be 
periodic chances for scattered showers or a few isolated 
thunderstorms, particularly in the afternoon hours.  By Tuesday and 
through the remainder of next week, the upper ridge will begin to 
progress east, with heights building across the region.  At the 
surface, the high pressure that will cover the region through the 
weekend and early next week, will shift east, setting up a return 
flow of warm/moist air.  A warming trend will begin on Tuesday with 
highs increasing to the upper 70s.  The warming trend will continue 
through the week, with temps rebounding back to the lower to middle 
80s.  The next significant chance for precipitation will come by 
Wednesday night into Thursday as low pressure develops over the 
northern plains and tracks to the western Great Lakes.  Increasing 
warm/moist advection in advance of this system will bring increasing 
chances for showers and thunderstorms.


For the 00Z TAFs...

622 pm...Gusty west/northwest winds will diminish with sunset 
this evening but speeds in the 7-11kt range expected for much of 
the night. Speeds/gusts will increase again Saturday morning as 
the low levels mix with west/northwest winds gusting into the mid 
20kt range. There is a chance of showers late Saturday afternoon 
across northwest IL and rfd and then the rest of the area Saturday
evening. Confidence is fairly low and activity will likely be in 
a weakening phase during this time period so stayed dry with this 
forecast. cms


307 PM CDT

Low pressure over Quebec will continue to lift northeast while a 
trailing cold front pushes through the Ohio Valley. A series of
weak troughs and secondary surges of cooler air will push across
the western Great Lakes region, keeping winds generally
northwesterly through the weekend and into early next week. High
pressure building out of Canada will spread into the northern and
central plains over the weekend and then build over the Great
Lakes early next week. Low pressure will begin to develop over the
northern plains Tuesday night and Wednesday as the high slides to
the east. Increasing sly-swly winds will set up over the lake as
the low pressure and an associated cold front push across the
northern plains to the upper Mississippi Valley Wednesday night,
while the high more slowly moves off the mid Atlantic coast.
Increasing sly-swly winds up to 25-30 kt will set up over Lake
Michigan for Wednesday and Thursday and then diminish and turn
more westerly late next week following the passage of the cold





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