Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 202028

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
328 PM CDT Mon Mar 20 2017


Through Tonight...

156 pm...Bulk of the showers and thunderstorms have moved east
and southeast of the cwa this afternoon but much of the short term
guidance suggests there will be festering showers through late
afternoon across parts of northwest Indiana and possibly into the
early evening hours. Confidence is fairly low with how widespread
this activity may become as well as how long it may persist.
Maintained low chance pops into the late afternoon but trends will
need to be monitored.

A cold front is slowly sagging south across the cwa this
afternoon shifting winds north/northeasterly and as these winds
increase during the mid/late afternoon...a more noticeable drop in
temps will be seen closer to the lake with lows tonight dropping
into the 30s. Cloud cover is struggling to clear across northeast
IL and southern Lake MI and while trends do support clearing
conditions this evening...confidence is also low. cms


304 PM CDT

Tuesday night through Monday...

Northwest flow still anticipated to be in place and although high
pressure will build southeast across the region during this time,
still am monitoring for the potential of some light rain Tuesday
afternoon. Narrow axis of forcing/precip still possible mainly in
the afternoon, and for areas south of I-80. Confidence still not
overly great, with guidance varying to the extent of any precip.
Most locations will likely stay dry but did leave low chance
wording for rain for the far southern CWA. This forcing quickly
shifts to the southeast by Tuesday evening, as high pressure
really begins to shift overhead Tuesday night into Wednesday. Dry
but cool conditions then expected by midweek. Pattern still
appearing to be active by the end of the work week with
anticipated large upper level system likely slowly moving east
towards the region. As this occurs, showers and even thunderstorms
will become more probable, especially by the weekend.



For the 18Z TAFs...

1240 pm...Main forecast concern are the winds which have become
light and variable at many locations...with light southerly at
mdw/gyy. Over the next 1-2 hours winds are expected to shift to
the north/northeast with speeds under 10kts...but these speeds are
expected to increase to 10-15kt during the mid/late afternoon and
some gusts are possible. Winds are expected to remain mainly
northerly tonight...possibly shifting north/northwest Tuesday
morning and then turning back to the northeast Tuesday afternoon
with speeds 10-15kts and some gusts possible Tuesday afternoon.

Mvfr cigs will continue this afternoon and begin to scatter and
lift mid/late this afternoon. Current timing to scatter out mvfr
cigs may be a little too early and trends will need to be

Bulk of the showers/thunderstorms will remain well south of the
tafs this afternoon...though short term guidance does suggest some
shower activity is still possible late this afternoon across
northwest Indiana as winds shift northerly. Confidence is fairly
low at this time...but trends will need to be monitored for shower
potential this afternoon for gyy. cms


304 PM CDT

Surface trough extending from the central Plains to the mid
Mississippi valley will shift to the southeast this evening,
while high pressure well to the northwest builds across the
western Great Lakes. In the near term, this is resulting in
increased winds over much of the lake, but with the strongest of
15 to 25 KT occurring over the south half and nearshore waters.
Although northerly winds will persist, do think speeds will
diminish this evening back to 10 to 20 KT for much of the lake.
Further expansion of the high towards our region will allow winds
to increase once again during the day Tuesday but more so by
Tuesday evening. Winds approaching 30 KT are likely, with these
increased winds likely across the nearshore. This will likely
provide hazardous conditions for small craft very late in the day
Tuesday and Tuesday night.






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