Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 181152
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
652 AM CDT THU AUG 18 2016

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 358 AM CDT Thu Aug 18 2016

Abundant low level moisture, light winds and mostly clear skies
under a high pressure system has led to patchy dense fog across
northeast Wisconsin early this morning. Despite these ideal
conditions, the fog is very patchy and transient, with
visibilities bouncing back and forth quite a bit. Therefore will
not issue any headlines for the fog this morning. The fog should
dissipate a few hours after sunrise with daytime mixing.

The aforementioned high will slide east today as low pressure
develops across the northern Plains. Southerly winds between these
systems will allow temperatures to rise a few degrees today, with
highs in the lower to middle 80s. NWP and hi-res models do show
the potential for some isolated showers and thunderstorms this
afternoon, especially across the north where a weak shortwave will
track along the Michigan/Wisconsin border. Therefore will put a
slight chance for this activity today. This activity should wane
rather quickly with the loss of daytime heating this evening.

The bigger story will be thunderstorms that form over the upper
Mississippi Valley this afternoon and track east through the
western Great Lakes during the overnight hours. This activity will
have a shortwave associated with it, along with around 2000 J/kg
of MUCAPE as it tracks through Wisconsin. Therefore thunderstorms
that can track east tonight will still have a decent amount of
instability to work with, making for a marginal risk for severe
weather across the cwa with the main threat being wind damage and
to a lesser extent given the high freezing levels, hail.

The low pressure system developing over the plains today will
track east over the western Great Lakes on Friday. This will bring
a cold front over northeast Wisconsin on Friday, continuing the
chance for showers and thunderstorms. Severe potential on Friday
will be dependent on how morning convection affects the
atmosphere, however current indications are that enough
destabilization, around 1000 J/kg of MUCAPE, will occur ahead of
the advancing cold front for a marginal severe weather threat
across southwest portions of the cwa, across central Wisconsin.
Model soundings indicate the storms would mainly be linear in
nature with the main threat being damaging winds. Highs on Friday
will vary from the middle to upper 70s across north central
Wisconsin behind the cold front, with lower to middle 80s ahead of
the cold front across central and east central Wisconsin.

These multiple rounds of activity could cause localized flooding
across the area tonight and Friday, with the biggest threat across
north central Wisconsin given the highest expected QPF for these 2
periods. At this point will leave the ESF as is as current model
runs do not paint a significantly different picture from the
initial issuance.

.LONG TERM...Friday Night Through Wednesday
Issued at 358 AM CDT Thu Aug 18 2016

Cooler than normal weather will prevail for much of this forecast
period. Clouds and rain on the cool side of a frontal boundary
should result in below normal high temperatures for the weekend.
Highs are expected to be near normal on Monday with a surface high
over the region. Return flow on the back side of the high will
bring above normal temperatures back for Tuesday and Wednesday.

Though models differ in their depiction of a surface low moving
northeast along a cold front, they generally agree that it will be
rather wet across the forecast area, especially in northern
Wisconsin, through at least Saturday. Have likely or higher POPs
going for Friday night and Saturday for this reason. POPs drop to
chance for Saturday night with more significant differences among
the models.

Once the surface low and mid level trough pass to the east, it
should generally be dry for Monday and Tuesday. Models bring rain
chances back to parts of the area later Tuesday night and
Wednesday.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 652 AM CDT Thu Aug 18 2016

Patchy fog will quickly dissipate this morning with daytime
heating. After the fog dissipates, vfr conditions expected for the
rest of today. Mid to high level clouds will be on the increase
tonight ahead of a frontal system with showers and thunderstorms
moving in just after midnight as a thunderstorm complex moves
through the region.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......MG
AVIATION.......Kurimski



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