Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 260758

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
258 AM CDT Wed Oct 26 2016

258 AM CDT

Through tonight...

Shortwave trough and associated surface low will move across the
region today bringing inclement weather to the area today. Initial
wave of WAA driven showers moving through the area currently
should lift out of the area prior to sunrise. It appears as though
there will be a period of dry weather this morning, lasting
longest over southern portions of the CWA where next wave of
showers may hold off until late afternoon over portions of NW IN
and east central IL. Farther north, more widespread deformation
zone rain should settle ESE into far northern IL this morning and
provide for longer duration steady rainfall. Rain should taper to
a lighter rain or heavier drizzle this evening before ending
altogether by late evening/overnight.

It will be a cloudy day with increasingly strong/gusty winds this
morning, especially northern CWA where pressure falls should be
the strongest. Winds should peak mid-late morning through early
afternoon before tapering off toward evening as baggier gradient
near the surface low approaches. At their peak, winds midday could
gust over 30 mph, with gusts near 40 mph possible along the IL



258 AM CDT

Thursday through Tuesday...

Thursday will be another seasonably cool day with forecast
soundings suggesting we could hang onto a stratocumulus deck a
good portion of the day. Skies should begin clearing Thursday
night as warm air advection begins in advance of the next system.
models continue to track shortwave and fairly strong surface low
quickly east across the U.S./Canadian border Friday then east into
the St Lawrence Valley by Saturday.

Strong warm air advection Friday should allow temps to warm
rapidly into the 60s to near 70 as increasingly strong/gusty
southwest winds develop. Models continue to advertise the
strongest pressure gradient in our area Friday evening with
5-7mb/3hr pressure falls to our north likely to keep winds
strong/gusty despite sunset. Strong low level jet (50-60kt at
925mb) is forecast to be over our area Friday evening. Models
show 2m temps remaining essentially steady or even rising a degree
or two from 00z through 06z Saturday (Friday evening). The result
will likely be continued efficient mixing, which could tap into
some of that higher momentum air of the low level jet. Didn`t get
too carried away in the grids yet, but potential for a period of
near advisory level gusts (45 mph) are possible Friday evening.

The strong winds will keep temps largely steady in the 60s much of
the night Friday, though as front approaches late at night winds
should ease some and probably allow temps to drop off into the 50s
over NW portions of our CWA. Looks like a very mild start to the
day Saturday, but models have trended about 8-10 hours faster with
cold front sagging south across the CWA, which means much cooler
temps Saturday afternoon northern CWA based on current model
progged timing. High temps Saturday will be tricky and hinge on
the exact timing of fropa, particularly near Lake Michigan where
some lake enhancement of the front will know temps down even
farther near the lake.

Latest ECMWF has a shortwave trough riding the WNW flow aloft into
the region Saturday night and breaks out a healthy band of
rain/isolated t-storms north of the now stalled out front across
our CWA. GFS has a similar idea though a bit farther south.
Despite low confidence at this point, have opted to added pops to
the initially dry model blended cocktail grids Saturday night.

After a seasonable temps Sunday, another strong surface low is
forecast to track well to our north Monday. The result will be
another day of strong warm air advection and unseasonably warm
temps on Monday. Medium range models are currently forecasting
850 and 925 mb temps to be near or in some cases a few degrees
above records for this time of year. Have nudged temps up in the
model blend that we initial our forecast with, but remained
conservative with increases as there is still time for models to
slow or speed up the timing the front and warmest air. It is worth
noting that if the warmer solutions pan out, then temps near or
even reaching 80F would be well within reach!! Another weak cold
front is progged to bring an end to the unseasonable warmth Monday
night, though temps look to remain solidly above average into at
least the middle of next week.



For the 06Z TAFs...

No real big changes to the going TAFs, as current forecast is
handling approaching and anticipated precip this morning. Latest
radar imagery depicting area of light showers moving east through
northern Illinois. This precip will continue to steadily move east
through early this morning and although there may be brief periods
of moderate intensity, light showers will likely be more
prevailing. After a lull later this morning, upstream moderate
showers will then swing through by midday into the afternoon.
Main concern going into the afternoon will be with ceiling
trends. At this time, trends would suggest that low MVFR and IFR
ceilings won`t arrive until late this afternoon and evening.
However, there is a possibility for an earlier arrival in the
afternoon and will continue to monitor this possibility. Precip
exits later this evening, but low ceilings will likely hang on
through the period. Southeast winds will steadily increase this
morning into the afternoon, and then confidence with wind
direction and speed later this evening is low as an area of low
pressure pushes over the terminals. Have left the variable winds
in the forecast given the track of the low, but the direction will
then turn west northwest later in the evening on the backside of
this system.



308 PM CDT

The main weather concern for Lake Michigan continues to focus on
a period of southeasterly gales expected on Wednesday. Overall,
expect the winds to become easterly tonight, while gradually
increasing up to 30 KT by early Wednesday morning. Winds will then
become southeasterly up to 40 KT Gales during the day Wednesday as
the surface pressure gradient strengthens in response to an
approaching eastward moving surface low. The strongest winds are
still expected across the southern half of Lake Michigan,
including the Illinois and Indiana near shore waters. Winds should
then abate and become northerly in the 15 to 25 KT range for a
period late Wednesday night into Thursday as the surface low moves
towards the eastern lakes region.

Surface high pressure will then build over the region by late
Thursday. This should set up a period of light winds, generally
under 15 KT for Thursday and Thursday night. However, as this
surface high shifts east of the area on Friday, winds will
increase out of the southwest as another storm system takes shape
over the Northern High Plains. A period of winds of 25 to 30 KT
will be possible over southern Lake Michigan late Friday and
Friday night. This looks to result in hazards conditions for small
craft for the Illinois and Indiana near shores. This surface low
is finally expected to pass eastward somewhere over Lake Michigan
by Saturday evening. In its wake, there could be a period of
strong northwesterly winds into Sunday.



LM...Gale Warning...LMZ777-LMZ779...7 AM Wednesday TO 10 PM Wednesday.

     Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...7 AM
     Wednesday TO 7 PM Wednesday.




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