982
FXUS63 KGRB 060338
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1038 PM CDT Fri Jul 5 2024

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Flooding will continue along the Little Wolf River downstream of
  the Manawa dam. Do not drive across flooded roadways if
  traveling through this area.

 - Patchy dense fog is possible over north-central Wisconsin
   after midnight.

 - On and off chances for showers and thunderstorms will continue
   from Sunday through Wednesday. Although the severe weather
   threat is low, locally heavy rainfall will be possible.

&&

.DISCUSSION...
Issued at 227 PM CDT Fri Jul 5 2024

Short Term...Tonight and Saturday

The latest RAP analysis and satellite/radar imagery show surface
low pressure moving east between Sheboygan and Milwaukee early
this afternoon. Clusters of showers and thunderstorms have
developed north of this low track in the 925-850mb moisture
convergence zone ahead of the 850mb low and base of the shortwave
trough. These clusters of showers/storms have been augmented by up
to 800 j/kg of mixed layer cape and precipitable water values
(pwats) of 1.30 inches, which is about the 75th percentile. As a
result, and in combination with relatively slow storm motion
(around 12 kts), storms have been prolific rain producers of 1-3
inches per hour and have been locally much higher (Waupaca was
estimated over 5" per hour). The heaviest precipitation will
likely exit east-central Wisconsin by around 4 pm. A Flash Flood
Watch is in effect until 7 pm this evening.

Tonight...Low pressure will continue to track east over the Lower
Peninsula of Michigan and Lake Huron. Cyclonic flow around the low
will continue this evening with low levels remaining moist beneath
the upper trough. A few showers will therefore remain possible
into the evening, but heavy rainfall will not be a threat. Then at
least partial clearing is expected late in the evening and
overnight from northwest to southeast. The clearing skies and
light winds will promote ground fog formation over north-central
and central Wisconsin as forecast temps fall below the cross-over
temps by early overnight. Lows will fall into the 50s except near
the Lake Michigan shoreline.

Saturday...Flattened troughing aloft will remain over the area.
Should see strong solar insolation during the morning, which will
lead to convective cloud development by late morning. Convective
temps are quite low, and only in the middle 70s. With highs in the
upper 70s to near 80 degrees, upwards of 1000-2000 j/kg of
surface based cape is expected which should result in
shower/thunderstorm develop by early to mid afternoon. CAMS
indicate areas along the lake breeze and bay breeze convergence
stand the highest chance showers/storms, but cannot rule out
spotty showers elsewhere either.

Long Term...Saturday Night Through Friday

Focus in this part of the forecast centers around severe and heavy
rainfall potential during the Sunday through Tuesday time frame.

Sunday through Tuesday...Upper troughing will remain in place from
the northern Plains to the western Great Lakes.  Impulses moving
through the trough will provide periods of showers and storms.  The
first of these troughs is located north of Montana and poised to
reach central Minnesota by 7 am Sunday.  This trough with help from
daytime instability of 1000-2000 j/kg will help trigger showers and
storms.  An isolated severe thunderstorm threat may develop in the
afternoon given the deep layer shear around 30 kts.  The heavy
rainfall risk looks low given the forward storm motion around 20 kts
and pwats just slightly over the mean for the date.

Secondary shortwave impulses are forecast to cross the area on
Monday and Tuesday.  Slightly less favorable convective parameters
for severe weather will be in place on Monday due to less shear
aloft. But low convective temps will likely spell an uptick in
coverage and intensity of showers and storms with daytime heating.

More diurnally enhanced showers and storms will also be possible on
Tuesday.  Deep layer shear is even weaker by this point, so the risk
of organized severe weather is low.

Rest of the forecast...Relatively quiet mid-Summer weather is
expected for the rest of the week as the upper flow flattens.
Temperatures should trend slightly above normal by the middle of
next week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1037 PM CDT Fri Jul 5 2024

Clearing skies and wet ground could result in areas of dense
ground fog or low clouds late tonight. The areas most likely to
have dense fog or low clouds late tonight should be north of a
Merrill to Iron Mountain line, and possibly the area west of a
Green Bay to Oshkosh line and east of a Clintonville to Waupaca
line. If low clouds or fog materialize, it should dissipate by
13z.

A few hours of MVFR ceilings are possible between 13z and 16z
Saturday, otherwise VFR conditions and light surface winds are
expected. There could be a stray shower or thunderstorm in the
afternoon or early evening west of a Iron Mountain to Oshkosh
line.

&&

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

&&

$$

DISCUSSION.....MPC/MPC
AVIATION.......RDM