448
FXUS63 KGRB 062343
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
643 PM CDT Sat Jul 6 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Some rivers, creeks and streams across east-central Wisconsin
  will continue to run above bankfull due to recent rainfall.

- Isolated pop-up showers and thunderstorms late this afternoon and
  evening could be slow moving, so locally heavy downpours are
  possible. Most areas will remain dry though.

- A few thunderstorms on Sunday afternoon/evening could be strong
  with gusty winds, small hail and heavy rain. At this time,
  severe weather is not expected. On and off chances for showers
  and thunderstorms will continue Monday through Wednesday.
  Although the severe weather threat remains low, locally heavy
  rainfall will be possible.

- A warmer/drier summer pattern may be in store toward the end of
  next week.

&&

.DISCUSSION...
Issued at 246 PM CDT Sat Jul 6 2024

Short Term...Tonight and Sunday

The latest RAP analysis and satellite/radar imagery show several
shortwave impulses moving east across the northern Plains and
northern Mississippi Valley. Further east, conditions are more
stable thanks to shortwave ridging aloft. Surface instability is
estimated at around 600-900 j/kg over north-central WI and
eastern WI. This instability has led to a cu field across much of
the region, which has been the most agitated over north-central
Wisconsin. No showers have been observed so far, but it`s still
possible that a few showers could pop by late this afternoon.
Forecast concerns revolve around precip timing as the shortwave
energy upstream approach northeast Wisconsin on Sunday.

Precip chances: The chance of isolated showers and storms will
likely continue into the evening hours as both the RAP and HRRR
indicate instability will be slow to dissipate. After a lull in
the precipitation late this evening and overnight, shortwave
energy from the northern Plains will be approaching northern
Wisconsin by 7 am Sunday. Modest moisture advection and little in
the way of instability will lead to a swath of showers lifting
northeast across the area during the morning hours. These showers
look to be light and scattered in nature.

Redevelopment of showers and storms is relatively uncertain in the
afternoon. In general, models depict a favorable thermodynamical
profile for thunderstorm development with 1000-2000 j/kg of
surface based instability if showers and cloud cover do not impact
the heating curve sufficiently. These factors look to have a
greater impact over north-central WI than over the Fox Valley
where showers are expected to be more widespread in the morning.
But in general, the convective allowing models are unenthusiastic
about precip chances in the afternoon, probably due to a lack of
focused ascent. Have therefore lowered precip chances in the
afternoon. If details change and trends support a greater
potential for thunderstorm development, increasing wind fields
aloft (deep layer shear 25-30 kts) could support a strong to low
end severe thunderstorm.

Temperatures will be near normal tonight and Sunday.

Long Term...Sunday Night Through Saturday

Heat ridge will remain parked across the southwest CONUS, slowly
expanding eastward next week. Broad area of troughing will
prevail across the Great Lakes, with multiple embedded shortwaves,
keeping an unsettled pattern in place through at least
Tuesday/Wednesday. Chances for drier weather arrives at the end
of the week, but monitoring how strong and how far east the ridge
will get, along with the track of Beryl. Temperatures look to be
near or slightly above normal.

Sunday evening/night...chances for storms will continue as the
upper trough slowly works toward the region and a shortwave/jet
cross the state. Coverage looks to be isolated to scattered. The
better instability wanes by midnight, so chances for a few strong
storms look to be confined to the evening hours. Gusty winds and
hail would be the greatest threats. Will need to monitor for a
heavy rain threat as well, with PWATs climbing to around
1.25-1.75", possibly near 2.0" in east central WI and tall/skinny
CAPE profiles. If a scenario like the HRRR pans out, would have
some training storms which could drop some heavy rain totals over
an inch or two pretty easily which could create some hydro issues,
especially in central and east central WI. Recent rain could lead
to some fog development. It looks to be a fairly warm and muggy
night in the Fox Valley with lows in the upper 60s and dewpoints
in the mid 60s. Slightly cooler and less humid conditions are
expected further north.

Monday into Tuesday...upper trough slowly treks across the Great
Lakes, along with an upper jet and a couple embedded shortwaves.
This will keep showers and storms in the forecast, especially in
the late morning and afternoon/evening hours during peak heating.
Some pulse-like strong storm will be possible, but locally heavy
rain appears to be the biggest threat.

Rest of the period...chances for drier and warmer weather arrives
in the mid to late week timeframe, but trends with the remnants
of Beryl will need to be monitored as any westward shift could
bring some more rain/clouds into the area. Also a little worried
we will get at least clipped by some of the ridge riders next
weekend.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 642 PM CDT Sat Jul 6 2024

Isolated showers or thunderstorms north of a TKV to IMT line will
dissipate early this evening as daytime heating ends. The remainder
of the area will be mostly clear. Some ground fog could form late
tonight near Lake Michigan and the area just west of the bay. If
it does form, it should dissipate by 13z Sunday

A warm cold front will move across the region Sunday morning and
could produce some showers across central and northcentral Wisconsin.
An approaching cold front could bring scattered thunderstorms to
the area Sunday afternoon and night as it moves slowly across the
area.

&&

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

&&

$$

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