451
FXUS63 KGRB 191711
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1211 PM CDT Fri Jul 19 2024

Updated aviation portion for 18Z 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 18Z TAF Issuance
Issued at 1156 AM CDT Fri Jul 19 2024

Fair weather cumulus clouds will continue this afternoon,
generally from five to six thousand feet. The cumulus field
should dissipate by 02z with some high cirrus moving across
the area overnight. The fair weather cumulus clouds should
develop again between 15-17z on Saturday. A cold front will
move into northern Wisconsin on Saturday morning, bringing
chances of showers and thunderstorms to northern Wisconsin
Saturday afternoon and Saturday night. Some of the stronger
storms could contain gusty winds and locally heavy rain that
would reduce visibilities for pilots.

.KOSH...Cumulus clouds with bases of five to six thousand feet
are expected until about 01z Saturday. W-SW winds will remain
light and less than 10 knots through the TAF period. Fair
weather cumulus clouds will redevelop Saturday morning, generally
in the 15-17z time frame and continue through the afternoon. A
cold front will bring a chance of showers and thunderstorms across
northern Wisconsin Saturday afternoon. A few of these storms
could make it into KOSH Saturday evening. Westerly winds of 5 to
10 knots are expected Saturday and from the east 5 to 10 knots on
Sunday.

&&

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

&&

$$

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