Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 261936
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
236 PM CDT TUE JUL 26 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Wednesday
Issued at 235 PM CDT Tue Jul 26 2016

Main forecast focus to be on precipitation trends as a cold front
slowly drops south across the area and a shortwave trough
approaches from the west.

The 19z MSAS surface analysis showed an area of high pressure
stretched across southern sections of the Great Lakes with mostly
sunny skies and an uptick in relative humidity. A cold front
extended roughly from Lake Superior southwest to SD. While eastern
sections of the cold front were precipitation-free, thunderstorms
were taking place over north-central MN and eastern SD.

The cold front is forecast to drop south into northern WI this
evening and approach central/east-central WI toward daybreak. Even
with the loss of daytime heating, models indicate sufficient
instability (capes 1000-1500 J/KG and LI`s around -4) to interact
with persistent moisture transport and convergence/lift along the
front, to generate a chance of showers and thunderstorms primarily
along and behind the frontal bounday. This would place the highest
pops across the north with lesser pops farther south. Shear values
are weak (20 knots or less), thus the risk of severe storms would
be marginal at best. Min temperatures to be in the lower to middle
60s north, middle to upper 60s south.

The west-east orientated cold front will continue to slowly sag
south and only reach southern WI by 00z Thursday. Meanwhile, a
shortwave trough is expected to ride the W-NW flow aloft across
the Upper Midwest by Wednesday afternoon. Anticipate shower and
thunderstorm activity to increase in areal coverage as this
shortwave trough adds mid-level forcing to the moderately unstable
air mass over WI. Shear remains weak on Wednesday, thus the threat
for severe storms appears minimal, although an isolated damaging
wind gust cannot be completely discounted. Max temperatures will
be held in check somewhat with clouds/precipitation in the
vicinity. Look for reading to range from the middle to upper 70s
north, lower to middle 80s south.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 235 PM CDT Tue Jul 26 2016

Precipitation trends through Thursday will be the main forecast
concern.

A Canadian cold front should be situated just south of the
forecast area by Wednesday evening, and continue to shift south
before stalling out in northern or central Illinois on Thursday.
Models all depict a s/w trof moving through the area Wednesday
night, and combining with lingering moisture and instability to
produce moderate to locally heavy rainfall across mainly central
and east central Wisconsin. Will carry likely pops over our
southern counties.

Precipitation chances will taper off from northeast to southwest
late Wednesday night into Thursday, and should end by Thursday
evening as Canadian high pressure builds in. The Canadian high
will dominate through the weekend, bringing dry weather, much
lower humidity and cooler temperatures. Southerly return flow on
the western periphery of the high will bring warmer temperatures
early next week, along with a chance of thunderstorms by about
Tuesday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1223 PM CDT Tue Jul 26 2016

A cold front is expected to slowly drop south across WI starting
this evening across northern WI and eventually reaching southern
WI by late Wednesday. There will be a chance of showers and
thunderstorms associated with this frontal boundary, primarily
across the north tonight. As the front continues to sag south on
Wednesday, a mid-level shortwave trough is forecast to push
across the Upper Midwest and increase the areal coverage of
showers/storms across northeast WI, especially during the
afternoon hours. While VFR conditions would predominate over the
next 24 hours, expect some patchy fog later tonight and
precipitation to lower vsbys to MVFR conditions at times.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kallas
LONG TERM......Kieckbusch
AVIATION.......AK


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