Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 201756

Area Forecast Discussion
National Weather Service Green Bay WI
1256 PM CDT Sun Aug 20 2017

Updated aviation portion for 18Z TAF issuance
and new information added to update section

Issued at 1246 PM CDT Sun Aug 20 2017

Conditions favor some storms developing across the area this
afternoon and evening. It now appears central and north-central
Wisconsin are the most likely locations to be affected. Coverage
will probably be limited, but strong or severe storms can`t be
ruled out.

The situation for Monday is unclear. Some of the models bring a
complex east across the area during the morning. But it still
seems more likely that the main round of storms will be Monday
evening/night. Will attempt to get a better handle on this for the
afternoon forecast, but this may end up being one of those
situations where we need to wait and see how convection late today
and tonight develops before being able to figure out tomorrow.

.SHORT TERM...Today...Tonight...and Monday
Issued at 330 AM CDT Sun Aug 20 2017

Coverage and intensity of convection, along and near a frontal
boundary sagging southward across the area later through Monday,
will be the focus of this period.

Early this morning a surface frontal boundary extended from far
northwest Minnesota to the central plains. Convection over
Nebraska continues to dive southeastward along the mid level cap
edge. To the north, a short wave over northwest South Dakota and
the start of the westerlies, was producing convection. The onset
of the convection along the approaching front over northwest
wisconsin later today will will likely get enhanced as mid level
winds and shear increases. In terms of timing, this short wave
may reach the northwest half of the state before the front this
afternoon. Not sure how this will impact any severe potential at
this time, but with MU CAPES increasing to at least 1000 J/kg
this afternoon and evening, convection may develop ahead of the
front in the warm sector and turn out to be stronger, especially
during peak heating later today into early evening.

Will then focus showers and storms along the southward sagging
frontal boundary tonight into Monday. Progs suggest the front
stalls over central Wisconsin by daybreak Monday, leaving chance
pops over the south half of the forecast area and lower end or no
chance of convection across the north. Stronger dynamics to work
with the front will likely arrive after the Monday period.

.LONG TERM...Monday Night Through Saturday
Issued at 330 AM CDT Sun Aug 20 2017

Spotty convection is likely linger on into the beginning of the
longterm forecast Monday afternoon with the stalled front still in
the area. A more organized round of convection will develop in
the evening along a shortwave. MUCAPE values around 1000-1500 and
Bulk Shear up to 30-40 knots will support convective development
as the forecast area enters the right rear quadrant of a jet
streak aloft. Combined, the forecast area will see a marginal risk
of severe storms across central Wisconsin. The main inhibitors to
the strongest storms will be the timing of the front, which could
push further south by the time the shortwave arrives and take the
convection with it, and the possibility that instability remains
limited after convection earlier in the day. In any case, heavy
rainfall will be likely through Monday night.

Some showers will linger on early Tuesday before quickly coming to
and end by Tuesday afternoon and evening. Once this system pushes
through, quiet conditions will arrive for the rest of the week as
northwesterly flow aloft brings in high pressure conditions near
the surface.

Temperatures will be a few degrees below normal through the
midweek before coming back to around normal by the end of the

.AVIATION...for 18Z TAF Issuance
Issued at 1246 PM CDT Sun Aug 20 2017

A cold front will sag south into the area late today and tonight.
Scattered thunderstorms will accompany the front. Other that with
the storms, VFR conditions are anticipated. The front may sag far
enough south to allow winds over central and north-central
Wisconsin to weaken overnight. That favors fog formation. Added
some fog to the central and north-central WI TAF sites for now,
but may need to lower visibilities further in later TAFs,
especially in any areas that receive rain this afternoon.



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