129
FXUS63 KGRB 191113
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
613 AM CDT Fri Jul 19 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Dry weather is expected through midday Saturday. Showers and
  thunderstorms are likely across northern WI Saturday afternoon.
  Severe storms are not expected, but locally heavy rainfall may
  occur.

- A chance of showers and thunderstorms will be possible each
  afternoon from Sunday through the middle of next next. Severe
  thunderstorm potential is low.

- Temperatures will be near-normal for the next week.

&&

.DISCUSSION...
Issued at 357 AM CDT Fri Jul 19 2024

Short Term...Today...Tonight...and Saturday

A Canadian high pressure system has shifted south of the region,
but the northern periphery was still impacting GRB CWA early this
morning. Clear skies and light winds resulted in patchy fog
development, mainly over north central and central WI. Weak
northwest flow aloft was still in place across the western Great
Lakes.

The Canadian high will bring dry conditions today and tonight,
with scattered cumulus clouds developing this afternoon,
especially over C/EC WI. Highs will warm into the upper 70s and
lower 80s, along with comfortable dew points in the 50s. Lows
tonight should be in the 50s and lower 60s.

A back door cold front will sag south through northern WI Saturday
afternoon. A weak upper trough over the region won`t provide any
forcing, but increasing moisture (dew points in the lower to
middle 60s) and instability (CAPE around 1000-1250 j/kg) along the
front should lead to numerous showers and scattered thunderstorms
north of Hwy 29. With PWATs increasing to around 1.5 inches and
weak flow aloft leading to slow movement of any storms, there is
potential for locally heavy rainfall. Severe weather is not
anticipated, as deep layer shear is expected to be weak (5 to 15
knots). Highs will be mostly in the upper 70s and lower 80s.

Long Term...Saturday Night Through Thursday


The main changes to the long term forecast were a slight increase
in afternoon PoPs most days as models continue to support the
development of instability showers/storms for several days.

Upper pattern continues to feature a western U.S. ridge and
eastern trough. Northeast Wisconsin is on the western edge of the
trough, but there is very little upper forcing over the area. The
main feature to watch will be a frontal boundary which will
meander around the area this weekend into the middle of next
week. This boundary combined with daytime heating will lead to
the development of scattered afternoon showers and thunderstorms.

Overall, the severe thunderstorm potential looks low most days,
but not impossible if conditions line up just right. Any severe
potential should be isolated and short-lived. Similar to previous
model runs, soundings would support gusty winds, small hail, and
locally heavy rain.

This pattern looks to break down Thursday or Friday with upper
ridging and a surface high across Wisconsin. This would lead to
rain-free conditions.

Temperatures will be near normal, with daily highs in the upper
70s to low 80s, and daily lows in the 50s to low 60s.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 555 AM CDT Fri Jul 19 2024

Patchy fog in the Wisconsin River Valley should quickly mix out
by 13z. Scattered cumulus clouds (bases 5-6K feet AGL) should
redevelop by 16z and linger until around sunset. Fog looks to be
less likely tonight, as there will be a little stronger pressure
gradient and boundary layer winds in place, so have opted to
leave any mention of fog out of the TAFs. W-SW winds should
prevail in most areas, with speeds at or below 10 knots

.KOSH...Cumulus clouds, with bases of 5-6k ft AGL, are expected
to develop around 16Z, then persist until about 01z/Sat. W-SW
winds will remain light and less than 10 knots through the TAF
period.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....Kieckbusch/KLJ
AVIATION.......Kieckbusch