Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 231922

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
222 PM CDT Sun Oct 23 2016

141 PM CDT

Through Monday...

We are currently enjoying what will be our warmest day of the week
as a thermal ridge ahead of a cold front and modest southwest
winds have pushed readings into the upper 60s to lower 70s area
wide...even some mid 70s in Central Illinois. These numbers are
some 10 degrees or so above normal for late October.

Changes in the temperature department are seen on the horizon with
a peek at visible satellite this afternoon. There is an area of
status clouds marching southeastward in the colder air mass behind
the cold front. Some of these clouds will move through our region
tonight, but with the low tracking across Lake Michigan toward
Detroit the bulk of the precipitation of the front will miss to
our north. North winds behind the front will likely result in some
lake effect clouds though no precipitation other than maybe a
sprinkle across NW Indy as a stout inversion at 850 mb holds.

High pressure rebuilds quickly Monday bringing mostly sunny skies
but a return to more seasonal conditions under north-northeast
winds, with highs expected to peak in the 50s.




Monday night through Sunday...

222 pm...High pressure will be centered over the western Great
Lakes Monday evening and slowly shift east Monday night into
Tuesday. Light winds and clear skies to start will allow temps to
quickly drop with lows currently expected in the mid/upper 30s.
Clouds will be increasing overnight which may allow temps to
become steady or even slowly rise toward sunrise Tuesday morning.
Potential for some patchy frost but confidence from this distance
is fairly low.

Low pressure will develop over the central plains Tuesday and move
east to the southern tip of Lake Michigan Wednesday evening.
Models initially show what may end up as a narrow band of showers
developing from southeast MN through far northeast IL Tuesday
afternoon. Should be quite a bit of dry air to overcome at first
and maintained low chance pops during this time. Possible that
these showers become heavy/widespread enough for some light qpf
but confidence too low to bump up pops just yet. the
low approaches...these showers will become more widespread and
heavier Tuesday evening into Tuesday night and the trend has been
for these to drift further into northern IL...generally along/
north of pops have been increased and spread further
south accordingly.

As the low approaches on Wednesday...precip will continue to
expand across the area and there may not be much of a lull across
the northern cwa with periodic showers. How long/widespread precip
becomes will impact temperatures especially across the north.
Opted not to make any significant changes with lower 50s north...
near 60 south. Southeasterly winds will also steadily increase
Tuesday night into Wednesday as the gradient tightens with wind
gusts perhaps into the 30-35 mph range. Instability appears
sufficient for some thunderstorms especially across the southern
portions of the area and depending on the track of the low...a few
stronger storms are possible...but likely south of the cwa. Precip
begins to taper off Wednesday evening. As for storm total rainfall
amounts...around an inch still looks likely over the northern
cwa...tapering to a half inch or less for southern areas.

A ridge of high pressure will move across the region Thursday with
dry weather expected. Flow turns southerly Thursday night into
Friday ahead of a cold front that will move across the area Friday
afternoon or Friday night. Temps likely to warm back into the 60s
Friday but then significant differences result in low confidence
from Friday night onward. Gfs is progressive with this front with
a punch of colder air spreading across the Great Lakes region
while the ecmwf develops a surface low over the plains which then
moves across the southern lakes region Sunday maintaining an
unsettled pattern through the weekend. cms


For the 18Z TAFs...

-Gusty southwest winds shifting to west this afternoon
-MVFR cigs this evening
-North winds shifting to northeast on Monday

Mixing to about 2500-3000 ft today will support low to mid 20s gusts
this afternoon. Winds will be veering from SW to NW through the
afternoon and low pressure moves southeast through Wisconsin. As
this low moves east to Michigan tonight it will send a cold front
southward through the region. Model guidance depicts a continued
shift NW winds tonight, possibly going to northerly for at least a
period mid to late evening, especially closer to the lakefront.

There is an area of MVFR to lower VFR clouds in the cold air behind
the front across Minnesota. Many sources of guidance do not bring
a ceiling with these clouds as the low tracks away from the area
to the east, but there are hints from the NAM and the NARRE that
some of these MVFR conditions spread through the area mid to late
evening for at least a time overnight. Since a decreasing band of
clouds is forecast but with the NARRE showing a period of MVFR
this evening, have TEMPO`d that in to the TAFs closer to the lake.

High pressure will fill in behind the low on Monday which will result
in clearing skies and shifting winds to more of a NE direction
mid to late morning through the remainder of the day.



311 AM CDT

A ridge of high pressure centered over the central Great lakes
will shift to the east today as low pressure over the northern
Plains quickly moves southeast to southern Lake Michigan this
afternoon. With these two surface features moving through the
region today, expect widely varying wind directions and speeds. It
does appear that the strongest winds will initially be over the
southern end of the lake and nearshore waters for much of today.
With these higher winds, hazardous conditions for small craft will
develop this afternoon. This low will then quickly move east of
the lake tonight with winds shifting more northerly tonight into
Monday. Higher speeds of 15 to 25 KT and even 30 KT winds/gusts
will help waves build, with hazardous conditions for small craft
continuing tonight into Monday morning. Have issued an advisory to
cover these hazardous conditions today through Monday morning, but
could possibly see higher waves lingering slightly longer over the
Indiana shore on Monday. Winds will then diminish with building
high pressure Monday night into Tuesday. Next area of low pressure
expected to move towards the lake through mid week with higher
winds and waves returning. Will continue to monitor this period as
gales are still appearing possible on Wednesday.



LM...Small Craft Advisory...INDIANA NEARSHORE WATERS UNTIL 1 PM Monday.

     Small Craft Advisory...ILLINOIS NEARSHORE WATERS UNTIL 10 AM Monday.




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