Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 210601

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
101 AM CDT Sat Apr 21 2018

158 PM CDT

Tonight through Saturday...

Quiet weather takes us into the weekend, though increasing
mid/high clouds and modest easterly winds will keep temps near but
just below average.

Early afternoon surface analysis indicates surface high pressure
spread across the upper Mississippi Valley and western Great Lakes
region. Dry air, plenty of sun and light winds have produced a
pleasant spring day, though a lake breeze has pushed in off the
lake keeping lake shore areas in the 40`s this afternoon while
other areas approach 60 degrees. The surface high will continue to
drift eastward tonight and Saturday, becoming centered across the
central and eastern Lakes by Saturday evening. Further west, a
closed upper low near the four corners region will cross the
southern Rockies by tomorrow morning, with diffluent upper level
flow downstream into the Midwest resulting in an increase in mid
and high cloud cover across the region from late tonight through
the day Saturday. With low level winds from the east, and the
thickening high cloud cover, 925 mb temps are progged about 2C
lower than today, supporting max temps in the mid-upper 50`s for
the most part, while onshore winds again limiting locations along
the shore of Lake Michigan to the mid 40`s. Winds generally 10 mph
or less however, making it feel much better than last weekend.



233 PM CDT

Saturday night through Friday...

Saturday night through Monday: Quiet weather will continue through
the start of this forecast period as mid-level ridging crosses the
area while a mid-level lows drifts eastward across the southern
states. Filtered sunshine is expected Sunday and Monday as a result
of passing mid to high-level clouds from the low to the south. This
should keeps max temps a few degrees below what would be expected
with the airmass over the area. Light easterly gradient flow will
also keep shoreline temps cooler.

Tuesday and Wednesday: Troughing over the northern Great Plains
will begin to cut-off from the larger-scale flow over the Upper
Mississippi River Valley Tuesday evening, with the low drifting
across Illinois on Wednesday. An associated surface low will cross
southern Wisconsin while weakening Tuesday night. Conditions
should remain dry through Tuesday afternoon, and likely Tuesday
evening, before the mid-level low nears. Given the lack of
organized forcing, will maintain chance PoPs for most of the area
late Tuesday night into Wednesday evening.

Thursday and Friday: A broad upper trough will redevelop across
eastern Canada and New England as the two aforementioned lows are
absorbed into a strong trough over the central U.S. While guidance
agrees on the development of this trough, there is disagreement
on the evolution. There should be a few chances for showers during
this time as temps drop back to seasonably cool levels for late



For the 06Z TAFs...

Surface high pressure will continue to prevail over the local
airports today, keeping winds mainly light apart from a lake
influence into the Chicago sites. This should push northeast
winds this afternoon to 7-8 kt, maybe sporadically higher.

Mid cloud will thicken by mid-morning with likely virga. Cannot
rule out patchy sprinkles today, but the very dry low-levels
should prevent any light showers.



101 AM CDT

Continued quiet weather over Lake Michigan through Monday night
with high pressure prevailing. This will present a variable wind
direction at times but with minimal speeds. A cold front will move
southward across the lake during or around Tuesday night bringing
northerly winds in its wake. This may present Small Craft
Advisory criteria conditions in the Illinois and Indiana
nearshores into Wednesday.






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