Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 221729

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1229 PM CDT Sun Apr 22 2018

214 AM CDT

Through tonight...

High pressure is centered over the eastern Great Lakes this
morning with ridging extending back into the Upper Midwest. An
upper low is over the Great Plains and will shift east across the
lower Mississippi Valley tonight. Precipitation is expected
across downstate Illinois on the northern periphery of the system,
but should be dry in the local CWA through tonight. Clouds are
expected to clear from the north as the upper low digs farther
south today, which should help temps achieve a few more degrees
today in many locations. Expect afternoon highs in the mid 50s to
low 60s away from Lake Michigan. An increasing easterly gradient
will keep areas near the shores of Lake Michigan much cooler in
the 40s. Clouds may begin to increase again tonight as the low
lifts towards the Tennessee Valley. Expect overnight lows in the
mid 30s to low 40s.



214 AM CDT

Monday through Saturday...

Upper low will continue to meander over the Tennessee Valley and
very gradually lift north across the Ohio Valley on Tuesday as the
low weakens and eventually opens up. Locally, expect much of the
area to experience extensive cloud cover along with a continued
chance for showers. Precipitation chances are mainly along and
east of the I-55 corridor which is a slight westward shift from
earlier forecasts. Winds will back to the northeast which will
continue to keep areas along the Lake Michigan shores in the 40s
and low 50s, but inland should see upper 50s and 60s.

Meanwhile, a pair of strong shortwaves will be in place over the
Pacific Northwest and British Columbia early this week. The
southern wave is expected to dig across the Central Plains into
the lower Mississippi Valley midweek while the northern wave digs
into the western or central Great Lakes. Strongest forcing misses
us to the north and south, so not a strong signal that northern
Illinois and northwest Indiana will get any precipitation. There
is a push of colder air into the midwest in the wake of these
waves which will result in only low to mid 50s for high temps on
Wednesday, but surface high building across the region will at
least result in otherwise fair weather conditions Wednesday and
Thursday. Another more robust cold front will sweep across the
area Thursday night into early Friday bringing a better chance
for showers. Temperatures cool briefly again on Friday with highs
in the low to mid 50s, but gradually moderate closer to normal
over the weekend.



For the 18Z TAFs...

VFR conditions will continue through the period. East northeast
winds have increased slightly today, with some gusts now likely
through the afternoon. Expect an east/northeast wind to persist
tonight into Monday.



124 AM CDT

Conditions continue fairly quiet over the lake through early
Tuesday. Northeast winds today and Monday will be stronger (10-20
kt) than recent days across the southern third of the lake. A
cold front will push down the lake on Tuesday night, turning winds
northerly with a sharp increase in speed. Small Craft Advisory
conditions are presently forecast all of Wednesday for the
Illinois and Indiana nearshores. Model solutions then largely
spread beyond that, with a blended solution of low pressure
dropping southeast over the Great Lakes late in the week.






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