Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 231923
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
223 PM CDT Mon Oct 23 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Tuesday
Issued at 223 PM CDT Mon Oct 23 2017

Plenty of forecast issues to sift through over the next 24 hours
as a strong autumnal storm impacts the Great Lakes. Headlines for
winds will be needed as well as the cool air mass headed our way
which may bring mixed precipitation into play Tuesday afternoon
across north-central WI.

The 19z MSAS surface analysis showed a weak area of low pressure
near the MN Arrowhead with a second area of low pressure over
northeast Indiana. Light rain showers or sprinkles were already in
southwest WI, while rain with the Indiana low was over the eastern
sections of Lake MI.

Models concur on the idea of merging the two low pressure areas
into one intense cyclone that is forecast to reside roughly over
eastern sections of Upper MI by 12z Tuesday. This will result in a
steady increase in winds from the northwest with gusts already
over 30 mph by late tonight. In addition to the winds, expect rain
to overspread northeast WI tonight as the strengthening surface
low passes by just to our east and an associated upper trough over
the Great Lakes closes off into an upper low, creating a nearly
vertically-stacked system. Min temperatures to be in the upper 30s
to lower 40s central WI, lower to middle 40s eastern WI.

The deep surface low is not expected to move much on Tuesday,
keeping both the windy and rainy conditions intact through most of
the day. Daytime mixing could have wind speeds reach advisory
conditions on Tuesday, especially closer to the surface low. Door
county would be most susceptible with a northwest component to
the wind and additional destabilization of the colder air moving
over the warmer waters of the Bay. After collaboration with
surrounding offices, have decided to issue a wind advisory for
all, but Door County from 12z Tue to 00z Wed. Have kept Door
County in a high wind watch for now as the situation is borderline
between advisory versus warning and any small shift of the
surface low track could tip the scales one way or the other.
Temperatures will not move much from morning lows, with readings
only in the lower 40s north, middle to upper 40s south. In fact,
parts of north-central WI could see some light snow mix with the
rain late in the day. Bottom line here is to look for a windy,
raw, and wet day across the region.

.LONG TERM...Tuesday Night Through Monday
Issued at 223 PM CDT Mon Oct 23 2017

Winds and precipitation will be winding down Tuesday evening as a
strong low pressure system exits the northern Great Lakes region.
Winds across Door County are still expected to gust for a few
more hours into Tuesday evening as a tight pressure gradient
remains over the region. A vigorous PV anomaly tracking through
the western Great Lakes will bring a chance for additional rain or
snow showers late Tuesday night into Wednesday morning as it
moves through the region. Some light snow could accumulate across
north- central Wisconsin during this period, however given the
warm ground accumulations are expected to be fairly light.

The weather will dry out briefly Wednesday afternoon and Wednesday
night as a weak ridge of high pressure tracks through the western
Great Lakes region. The dry spell will be short lived as yet
another low pressure system moves through the area Thursday and
Friday. This system looks to be cold enough to produce mainly snow
across northern Wisconsin later Thursday night into Friday
morning. Although ground temperatures will still be a concern,
the prolonged period of all snow could yield some measurable snow
across northern Wisconsin late in the week.

Although no additional large low pressure system are slated to
track through the region during the weekend and into early next
week, the region will remain in a large wave trough, which will
mean continued chances for light showers at times as shortwaves
rotate through the region. During the extended below normal
temperatures are expected for the rest of the week and into early
next week, marking a departure from over a month of above normal
temperatures.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1230 PM CDT Mon Oct 23 2017

VFR conditions are expected through the early evening hours,
before the approach of an intensifying surface low to our east
brings both increasing winds and rain chances to northeast WI
tonight. Expect cigs/vsbys to drop to at least MVFR conditions
starting late this evening and continuing through Tuesday
morning. Cigs could briefly drop to IFR conditions late tonight.
The bigger story though could be the windy conditions expected to
develop late tonight and really rev up on Tuesday. Sustained
northwest winds at 20 to 35 mph with gusts of 35 to 45 mph will be
possible with the stronger winds across eastern WI. These winds
may persist into Tuesday evening before slowly diminishing as the
strong cyclone shifts to the east.
&&

.MARINE...
Issued at 223 PM CDT Mon Oct 23 2017

A strong autumnal storm is forecast to lift north into the Great
Lakes region tonight, remain nearly stationary on Tuesday, then
shift to the east Tuesday night. As the storm strengthens over the
region, winds will respond by increasing tonight and becoming
windy on Tuesday. Gale warning are already in effect for both the
Bay of Green Bay and the nearshore waters of Lake Michigan. It is
possible that conditions may approach storm warning criteria on
Lake Michigan if the storm becomes strong enough.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 7 AM to 7 PM CDT Tuesday for WIZ005-010>013-
018>021-030-031-035>040-045-048>050-073-074.

High Wind Watch from Tuesday morning through Tuesday evening for
WIZ022.
&&

$$

SHORT TERM.....Kallas
LONG TERM......Kurimski
AVIATION.......Kallas
MARINE.........Kallas



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