Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 251928

Area Forecast Discussion
National Weather Service Green Bay WI
228 PM CDT TUE OCT 25 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Wednesday
Issued at 227 PM CDT Tue Oct 25 2016

Main forecast focus remains on the incoming swath of precipitation
and trying to determine how much rain will fall with this system.

The 19z MSAS surface analysis showed a broad area of high pressure
that stretched from northern Ontario south-southeast through the
Great Lakes to the Ohio River Valley. Several weak areas of low
pressure were situated on the lee-side of the Rockies from
southwest SD to northeast NM. A tightening pressure gradient
between all of these systems has allowed winds to start increasing
across the Plains. Radar mosaic indicated a narrow band of rain
showers that extended from ND southeast through southwest WI to
southern Ohio. This precipitation has not moved much in any
direction so far today.

Models concur in consolidating and moving a weak area of low
pressure from the central Plains to the Upper MS Valley/Midwest
tonight. In addition, a strengthening mid-level trough of low
pressure is expected to move from the Central Rockies across the
Central Plains tonight. The influx of gulf moisture ahead of these
systems will send PW values to almost one inch by daybreak into
northeast Wisconsin, however this moisture will be fighting a dry
air mass from the retreating surface high. Models show the
moisture gradually winning out after midnight with rain showers
lifting north into central/east-central Wisconsin during the pre-
dawn hours. Northern Wisconsin should remain dry for most of the
night with precipitation arriving around sunrise. Min temperatures
to range from the lower 30s far north, to around 40 degrees south.

The surface low is expected to track east-northeast along a warm
front draped over far southern Wisconsin or northern Illinois by
00z Thursday. Meanwhile, the mid-level trough will lift northeast
into the western Great Lakes on Wednesday and provide for
increasing Q-G and frontogenetical forcing over WI. PW values over
central/east-central Wisconsin remain around one inch, thus a
soaking rain is anticipated with QPF amounts of 1-2 inches by
Wednesday evening. It will also be a blustery day with east winds
at 10 to 20 mph north, 15 to 25 mph with gusts to 30 mph south.
Temperatures are not expected to rise much with upper 30s to lower
40s north, lower to middle 40s south.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 227 PM CDT Tue Oct 25 2016

Zonal flow will persist across the region, with the midweek system
exiting early, and two additional Pacific systems affecting the
forecast area during the extended period. The Pacific origin of
the systems should ensure that precipitation amounts will be on
the light side, and temperatures will be near to above normal.
Fast zonal flow will also lead to typical timing issues, which
will be handled by sticking with the preferred model blend.

Low pressure will move through northern IL as a short-wave trof
shifts through the western Great Lakes Wednesday evening. Showers
will taper off as this system tracks east. Aside from a few
lingering showers near Door county on Thursday, dry conditions
should prevail.

Strong WAA is expected to develop Thursday night into Friday,
with a low-level jet cranking up to 40 to 50 kts on Friday.
Despite a lack of moisture, there may be enough forcing to
generate some showers over northern WI Thursday night through
Friday night, with a cold frontal passage bringing a better chance
to the entire region Saturday into Saturday night.

A brief period of dry weather is anticipated on Sunday before
strong WAA brings another chance of rain Sunday night into
Monday, followed by another cold frontal passage Monday night.

.AVIATION...for 18Z TAF Issuance
Issued at 1241 PM CDT Tue Oct 25 2016

VFR conditions will continue through the evening hours, however
flying conditions are expected to gradually deteriorate from south
to north late tonight into Wednesday morning as a weak surface
low and mid-level trough approach from the southwest. Rain showers
are forecast to reach central and east-central Wisconsin before
daybreak and reach the U.P. of MI by mid-morning Wednesday. Once
the precipitation begins, cigs/vsbys will drop into the IFR range
with local LIFR condition under heavier bands of rain. The poor
flying conditions are expected to persist through the daylight
hours of Wednesday and may not improve until late Wednesday night.
In addition to the incoming rain, blustery conditions are expected
and have inserted LLWS into the TAF`s for late tonight/Wednesday
morning with wind speeds rapidly increasing just above the



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