Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 202348
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
648 PM CDT Fri Apr 20 2018

.SHORT TERM...
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.

Ratzer

&&

.LONG TERM...
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
April.

Kluber

&&

.AVIATION...
For the 00Z TAFs...

No significant aviation concerns next 24-30 hours.

Surface high pressure will continue to slowly drift east across
the area tonight. A lake breeze pushed inland early this
afternoon, turning winds at ORD/MDW to ely at 10-13kt, while the
remainder of the area saw calm or light variable winds
predominant. At sunset, expect the lake breeze boundary to wash
out and winds will become lgt/vrbl across the region overnight
tonight and through tomorrow morning. With a very dry air mass in
place in the lower levels, VFR conditions will prevail, though
with thickening and gradual lowering of high and mid cloud late
tonight into the day Saturday.

&&

.MARINE...
233 PM CDT

Generally quiet conditions with winds under 20 knots are expected
for Lake Michigan through Tuesday as high pressure drifts across the
western Great Lakes. Weakening low pressure will cross southern Lake
Michigan early Wednesday morning as a ridge builds into the Upper
Mississippi River Valley, supporting a period of northerly winds to
25 knots Wednesday into Wednesday night.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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