Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 122315

Area Forecast Discussion
National Weather Service Green Bay WI
615 PM CDT Wed Aug 12 2020

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 245 PM CDT Wed Aug 12 2020

Convective activity associated with a weak upper trough should
continue to dissipate as it moves into drier air across central
and northcentral Wisconsin. It is possible that a brief shower
could make it to Vilas county tonight, but think it should be dry.
Increasing high clouds will keep low temperatues higher than the
last couple days- close to seasonal normals.

Upper ridging moves into the region Thursday, with a weak surface
high off to our east. This should result in mostly sunny skies
and temperatures about five degrees above normal.

.LONG TERM...Thursday Night Through Wednesday
Issued at 245 PM CDT Wed Aug 12 2020

Forecast concerns mainly revolve around the thunderstorm potential
on Friday night and Saturday when a cold front moves across the
region.  This cold front will mark a pattern change when a large
trough will become established across the Great Lakes.  No clear
model preference, so will use a general model blend.

Thursday night through Friday night...A high pressure ridge axis
will initially be centered across the region on Thursday night, but
will gradually retreat to the northeast through Friday afternoon.
Mid-level warm advection will be taking place on Thursday night,
with some indications of convective clouds brushing across north-
central WI.  Both instability and moisture transport remains meager
though, so will leave the forecast dry despite the GFS spitting out
light qpf.  A strong cold front will then move across the northern
Mississippi Valley on Friday.  Position of the front along with
convective parameters suggest thunderstorm activity will remain well
west of the region through 7 pm Friday. The remnants of this
thunderstorm activity may approach north-central WI by late Friday
night, but instability will likely have weakened significantly by
this time. Highs on Friday will remain toasty in the middle 80s.

Rest of the forecast...The cold front will move across the region on
Saturday.  Still some timing differences, but potential exists for
the front to impact the region near peak heating when instability
could reach as high as 1000 to 1500 j/kg.  Deep layer shear of 25-30
kts could generate a few strong storms if timing remains on track.
Most of the storm activity will be exiting by early Saturday
evening.  A cooler and drier airmass will then gradually move into
the region behind the cold front.  Temps on Sunday will likely
remain near 80 degrees, but then highs slowly fall into the upper
60s to middle 70s by Tuesday.

.AVIATION...for 00Z TAF Issuance
Issued at 615 PM CDT Wed Aug 12 2020

A few sprinkles or light showers are possible this evening across
central and north- central WI as activity approaches from the
west, but most of this should dry up before getting here. Did not
mention -SHRA in any TAF sites as confidence and expected
duration is low. Meanwhile, middle and high clouds will continue
to advect into the area this evening and overnight, but VFR
conditions should prevail with light winds out of the S/SE. Some
uncertainty on how fast clouds clear out Thursday, but any
ceilings will remain VFR.



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