Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 270736

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
236 AM CDT Tue Jun 27 2017

235 AM CDT

Today and Tonight...

Dry and slightly warmer weather can be expected today as high
pressure develops into the region from the west. Cloud cover will
increase late tonight as winds shift south and begin to pull
warmer and more humid air back into the area.

Upper trough which has lingered over the Great Lakes region for
the past several days will move east today, nudged by Plains upper
ridge which will build in from the west through tonight.
Subsidence, indicated by 50-60 meter 500 mb height rises and
building surface high pressure, will result in mostly sunny and
dry conditions today, along with slightly warmer temperatures.
Model 925 mb temps of +15-17C should support mid-upper 70`s for
afternoon highs this afternoon. Weak lake breeze is expected, as
boundary layer winds start out less than 10 kts today, though a
gradual increase in 950 mb winds later this afternoon should limit
the inland push across the Chicago area. NW Indiana will likely
see the lake breeze push a little farther inland as winds start
the day NW there.

Winds turn south tonight as surface ridge moves east of the area.
This should help keep temps in the 55-60 degree range for
overnight lows. High cloud cover will likely increase toward
morning especially across western parts of the cwa, in association
with overnight thunderstorm complex progged to develop across
IA/MN and western WI. This activity expected to remain west of the
cwa until after sunrise Wednesday morning.



235 AM CDT

Will be issued shortly.


For the 06Z TAFs...

Quiet aviation weather anticipated through this forecast period.
How far inland the lake breeze develops is the only real concern,
with the greatest potential for a wind shift at GYY.

Upper level trough which has plagued the area since the weekend
was shifting east of the area early this morning. Strong subsidence
was developing in the wake of this feature was indicated by 50-60
meter mid-level height rises. At the surface this translates to
high pressure working east-southeast across the forecast area
today. Light low-level wind fields in the vicinity of the high
pressure ridge axis (around 5 kts at 950 mb this morning) should
allow lake breeze to develop by midday, though gradual eastward
shift of the ridge this afternoon and modest increase in southwest
flow just above the surface will likely limit how far inland it
moves. High-res guidance generally depicts winds turning northeast
at GYY by early afternoon, though indicate the lake breeze boundary
will stall just east of ORD and MDW during the afternoon. Winds
then become light south-southwest this evening as ridge continues
to move off to the east.

Otherwise...VFR conditions expected through the period with just
few-sct cu and high cloud at times.



233 PM CDT

Northwest winds have increased to 20-25 kt across the nearshore
waters. Winds will become even more northwest as a cold front moves
through this evening. Winds diminish to where a small craft advisory
will not be needed for the IL shore early this evening. However,
waves in the Indiana nearshore waters will remain hazardous past
midnight and slowly subside overnight.

West winds become southerly Tuesday as the high pressure ridge moves
over the lake. The next low forms over the northern plains Tuesday.
The pressure gradient tightens over the lake Wednesday between the
high over the central Atlantic Coast and the low over the northern
plains. South winds may increase to gales Wednesday. The low weakens
Thursday as it shifts east, and winds weaken and become west to

Another, weaker low may move over the southern end of the lake
Friday afternoon/evening.  West winds are expected behind the low
through Sunday.



IN...Beach Hazards Statement...INZ001-INZ002 until 4 AM Tuesday.

LM...Small Craft Advisory...IN nearshore waters until 4 AM Tuesday.




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