Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 182326

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
526 PM CST Sat Nov 18 2017

237 PM CST

Through Tonight...

Area of precip will continue to steadily depart to the east late
this afternoon into the early evening. The overall trend of rain
transitioning over to a rain snow mix, and then briefly all snow
will continue this afternoon. As deeper moisture is lost, have
been seeing a change back over to all rain before the precip ends,
with this also continuing. Additional lake effect precip will
likely occur for a time across far northwest Indiana this evening,
but anticipate the main focus to stay just to the east. As CAA
continues, temps will steadily drop through tonight with lows in
the 20s still expected. Gusty winds still anticipated through
tonight, with gusts of 35-40 MPH still likely. Winds may
periodically be stronger for locations right near the lake,
especially in northwest Indiana.



209 PM CST

Sunday through Saturday...

After precipitation ends today, expect primarily dry conditions to
be in place across the region at least until near the end of the
upcoming week. Primary forecast challenge will be dealing with
fluctuating temperatures as a series of clippers track just to
our north over the upcoming week.

On Sunday, the strong low that impacted the region today will
continue to depart lifting across Quebec while high pressure
builds  across portions of the Great Plains and Midwest. Thermal
trough behind the low will move across the western Great Lakes
through the day Sunday and will keep temperatures on the cooler
side with highs topping out only near the freezing mark. Cold air
stratocumulus should be in place early in the day but there is a
chance we could see some peeks of sunshine later in the day as
corridor of stronger mid level height rises and subsidence behind
the 500mb trough axis pivots across the area and low level
anticyclonic flow increases.

Throughout the upcoming week, upper low will generally remain in
place over Hudson Bay while several waves pivot across the Great
Lakes region with the baroclinic zone undulating across the local
area. Forecast soundings indicate dry air will be in place through
the week, and the best forcing will remain to our north with the
passing waves, so do not anticipate any precipitation but
temperatures will fluctuate back and forth. The first wave will
move across the upper Great Lakes Monday with southwest flow out
ahead helping us to warm back into the upper 40s. Cold air behind
the wave will spill back across the region through the day
Tuesday. Depending on fropa timing, some areas will see morning
highs with falling afternoon temperatures. This makes temps a bit
tricky with highs in the mid to upper 30s northwest with earlier
fropa to mid to upper 40s in the southeast. Temperatures fall back
into the low to mid 20s area-wide Tuesday night into Wednesday
morning and only rebound to near the freezing mark Wednesday. This
cycle repeats itself late in the week as another wave digs across
the Great Lakes late Thursday followed by a third wave over the
weekend. This final wave is the furthest south and has the best
chance of producing precipitation across northern Illinois and
northwest Indiana Friday night into Saturday.



For the 00Z TAFs...

Concerns with the TAFs through Sunday are mainly just winds this
evening, along with periods of MVFR clouds into Sunday morning.

The weather system (low pressure) responsible for the gusty winds
and precipitation is pulling well away from the area, now
northeast of Cleveland. With the system center inching north of
our latitude, the wind direction at ORD and MDW is likely to back
to more prevailing 330 degrees by 01Z (as opposed to 340-360
degrees). Gusts into the mid 20 kt are likely this evening with
sporadic upper 20 kt gusts possible early this evening. These will
inch downward overnight, though west-northwest gusts in the upper
teens are likely on Sunday.

The back edge of the MVFR clouds is passing RFD as of 23Z,
however, the cold advection pattern and limited drying may support
more broken MVFR cloud development tonight. Satellite trends are
indicating this across western Wisconsin. So have leaned more
toward broken throughout early morning at ORD and MDW, but at
least brief scattering is probable late evening and overnight. The
low-levels should dry out sufficiently by late Sunday morning
with only some cirrus then.



209 PM CST

North winds have been steadily strengthening through the day today
as low pressure lifts from northeastern Indiana this afternoon to
Lake Ontario this evening. Expect strong gales to peak around 45
kt late this afternoon and evening then very gradually diminish
overnight dropping back below gale force early to mid Sunday
morning. Winds remain moderately strong to around 30 kt through
the rest of the day Sunday and will back to the southwest Sunday
night into Monday as another low moves east across the Canadian
Prairies. Winds will strengthen back to gale force Monday
afternoon and continue through much of the day Tuesday as the low
tracks just north of Lake Superior and then lifts to James Bay.
The pattern will remain active late in the week into the weekend
and cannot rule out additional periods of gales late in the



IN...Lakeshore Flood Advisory...INZ001-INZ002 until 3 AM Sunday.

LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 until 6 AM Sunday.




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