Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 150826

Area Forecast Discussion
National Weather Service Green Bay WI
326 AM CDT Sat Jul 15 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 326 AM CDT Sat Jul 15 2017

The primary concern is the severe thunderstorm potential this
afternoon and evening.

Early this morning satellite imagery showed a weak short wave
sliding over northern Minnesota and adjacent Canadian region.
Radars to the west show a diminishing trend of light precipitation
over Minnesota as the trough moves away from marginal instability
and into the more stable surface high pressure region over
the Western Great Lakes region. The primary short wave trough was
sliding over North Dakota early this morning and will dive
southeast over the western Great Lakes region in response to the
building upper ridge over the plains. H850 mb temps were on the
increase this morning but the warm prod was located over Minnesota
and northwest Wisconsin. Will keep the dry forecast going through
at least noon.

Will increase pops this afternoon as a cold front drops into far
northwest Wisconsin and the primary short wave drops in. Surface
dewpoints in the mid to upper 60s over Iowa not far away and will
lift into the state this afternoon ahead of the front producing mu
capes around 2000 j/kg. This combined with the increasing deep
layer shear due to increasing northwest flow aloft, continues to
highlight much of the forecast area in the slight risk region for
day 1, and centered over central Wisconsin. Initiation of storm
cells will likely be focused with the convergence along the front
and then persisting due to the available instability and deep
layer shear. Forecast soundings are showing some capping early
this afternoon to be overcome and convection may be limited if the
front and short wave progress faster. Mid level northwest winds
expected to drop the front southward quickly, perhaps departing
Manitowoc county by late evening to end the convection across the

Canadian high pressure will drop into the area late tonight into
Sunday for a dry quiet period. Breezy northeast winds along lake
Michigan may produce slightly cooler temperatures Sunday.

.LONG TERM...Sunday Night Through Friday
Issued at 326 AM CDT Sat Jul 15 2017

Low amplitude upper flow is expected during this part of the
forecast. The flow starts out with a ridge departing the area,
followed by pretty much zonal flow before veering and becoming
west-northwest during the latter half of the week.

Dry conditions are expected to prevail through Monday evening but
an approaching mid level short wave and a surface cold front bring
chances for showers and storms back to north central Wisconsin
later in the Monday night. PoPs increase across the forecast area
from northwest to southeast, with the best chance for showers and
storms Tuesday night. Models generally have a hard time with
short waves in low amplitude flow aloft, and the cold front will
not move much after it clears the state, so there are chance PoPs
in the forecast through Thursday to account for the
uncertainty/differences among the models. No more than slight
chance PoPs Thursday night or Friday at this point.

Highs on Monday will be below normal, but daytime temperatures
warm quite a bit for Tuesday and remain near or a bit above normal
through the end of the work week.

.AVIATION...for 06Z TAF Issuance
Issued at 1042 PM CDT Fri Jul 14 2017

Mostly clear skies will continue during the overnight hours. are
anticipated tonight. Mostly clear skies and light winds have led
to some MVFR fog across portions of north-central Wisconsin. Will
add fog to the fog prone areas overnight as temperatures continue
to drop, with some areas potentially falling to IFR during the
overnight hours. A cold front is expected to move into the
western Great Lakes Saturday afternoon, setting off showers and
thunderstorms through the evening hours. Continued to time some
thunderstorm chances in the TAFs from north to south with the
front with this TAF issuance during the afternoon and evening



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