Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 130334

Area Forecast Discussion
National Weather Service Green Bay WI
1034 PM CDT Tue Sep 12 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 240 PM CDT Tue Sep 12 2017

Fog is the main forecast challenge tonight. An upper ridge and
surface high should provide ideal conditions with clear skies and
light surface winds. The best low level moisture and lightest
winds in boundary layer will be across eastern Wisconsin tonight,
so the best fog potential might be there instead of central and
northcentral Wisconsin like last night.

Surface winds in northcentral Wisconsin usually become light and
variable or calm with these conditions, but models have 925 mb
winds increasing to 20 to 25 knots late tonight, which might
reduce chance of dense fog. This is one of the best times of the
year for ground fog, so am guessing that there will be sufficient
fog for a dense fog advisory later tonight for at least part of
the area. Lows tonight will be closer to normal for this time of
the year.

Wednesday should be mostly sunny and warm once any fog dissipates.
Highs will be close to 80F in most places, along with dewpoints
typical of a summer day.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 240 PM CDT Tue Sep 12 2017

Conditions are expected to hold fairly steady through the work
week as our area remains between the remnants of `Irma moving
across the Ohio Valley, and the upper level trough over Canada.
Above normal temperatures will persist with only a few chances of
showers until the latter part of the weekend.

Above normal temperatures are expected as southwesterly flow
persists across the area on Thursday. The main region of
frontogenesis is expected to stay north in the Upper Peninsula
through Saturday, but a few showers could graze the area in
northwestern Wisconsin and parts of Vilas County. An upper level
trough accompanying a cold front could bring some showers to the
western parts of the state, but should also stay our of our area
until the Saturday night.

As the finally remnants of Irma out of the Ohio Valley, the upper
level trough will approach the region along with its associated
cold front at the surface. Cloud cover will move in Saturday night
into Sunday, with a good chance to see active weather across the
region. Instability is more marginal at this time, but with some
CAPE values rising to around 1000 J/kg and some moderate shear
around 30-35 knots through Sunday afternoon, thunderstorms will be
possible across the region. Temperatures behind the cold front
will drop back closer to normal, putting an end to the above
normal highs in the earlier parts of the forecast.

.AVIATION...for 06Z TAF Issuance
Issued at 932 PM CDT Tue Sep 12 2017

Areas of ground fog are likely again late tonight into early
Wednesday morning, with conditions below minimums between 08z and
13z possible at some locations. Focus for fog tonight will be from
central to northeast WI, though at least patchy ground fog will be
possible everywhere. Whatever fog does materialize should
dissipate by 14z with VFR conditions Wednesday afternoon and




LONG TERM......Uhlmann
AVIATION.......MPC is the U.S. government's official web portal to all federal, state and local government web resources and services.