668
FXUS63 KGRB 161151
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
651 AM CDT Sun Jun 16 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Showers and scattered thunderstorms are expected to exit
  northeast Wisconsin late this morning or early this afternoon.
  Heavy rainfall is likely, especially north and west of the Fox
  Valley. High rainfall rates may result in localized urban flooding
  and ponding on roads.

- Another round of thunderstorms is possible tonight. A few storms
  may become severe, especially over north central Wisconsin.
  Large hail, gusty winds and heavy rainfall will be the main
  threats.

- Well above average temperatures are expected Sunday through
  Tuesday. Heat indices may reach the lower to middle 90s at times
  Monday and Tuesday across central, east central and portions of
  northeast Wisconsin.

- Periodic thunderstorm chances are possible through mid-week.
  Some strong storms and locally heavy rainfall may be possible at
  times.

&&

.DISCUSSION...
Issued at 407 AM CDT Sun Jun 16 2024

Short Term...Today...Tonight...and Monday

Several clusters of showers and storms were ongoing across WI,
eastern MN and NE IA early this morning, but coverage varied
considerably. These areas of convection were being driven by a
combination of WAA with a 45-55 kt low-level jet, and a couple
MCVs; one over NW WI and another in NE IA. Elevated instability
was edging into the western part of the forecast area, where
a narrow band of storms was developing. PWATs had increased to
1.5 to 1.75 inches over western WI. At the surface, a warm front
extended from southern MN into SW WI.

Overall, the timing of today`s short-waves/MCVs is a bit slower
than was depicted the past few days. Have slowed down the
departure of the precipitation by a few hours, which will likely
delay the northward push of the warm front. Consequently, have
lowered max temps by several degrees and kept extensive cloud
cover around longer into the afternoon. Not expecting much
additional precipitation after the inital surge shifts northeast
of the region, but kept slight chance pops in northern WI, where
the warm front will likely reside later this afternoon. High
temperatures should range from the middle to upper 70s north to
the middle 80s south.

Tonight, a cold front is expected to edge into NC WI later this
evening and overnight. While models offer myriad possible
scenarios for convective development, suspect most of the
activity will occur near this boundary, so will keep the highest
pops over NC WI. With fairly strong elevated instability in place
and 30-40 knots of deep layer shear, a few strong to severe
storms could develop and produce large hail, gusty winds and heavy
rainfall. A short-wave trough is expected to approach NC WI late
tonight, and move through the Northwoods Monday morning. Have
increased pops to likely with this feature. The front will stall
out over northern WI on Monday, with resurgent southerly flow
resulting in overrunning during the afternoon. This should keep
the highest pops centered over northern WI. Farther south,
partial clearing could allow temperatures to surge into the upper
80s to lower 90s, with heat indices reaching the lower to middle
90s.

Long Term...Monday Night Through Saturday

An active pattern is shaping up next week as the 500mb ridge
across the eastern United States flattens by the end of the
upcoming work week. This will result in periodic chances for
thunderstorms through the entire work week, heat and humidity
on Monday and Tuesday with temperatures returns closer to normal
Thursday and Friday.

For Monday night, the close proximity to the warm front is enough
to keep the chances of thunderstorms during the evening across the
north. Although the forecast is dry overnight, the front is
relatively close and am concerned some convection will make it
into there. Will pass my concerns on to the day shift. For
Tuesday, the day should start out warm and humid as well as dry.
Daytime-heating with highs in the middle 80s to lower 90s are
expected. Bufkit soundings do show the cap weakening during the
afternoon, enough to support the chances of storms. Bufkit
soundings indicated around 2,000 J/Kg of CAPE with dry air in the
mid levels of the atmosphere. 0-6 km shear values are only around
20 knots, so pulse type storms are expected. The strongest storms
could produce wet microbursts/damaging wind gusts and hail.

For Tuesday night, showers and thunderstorms across Minnesota
may move east into the area. Stronger storms are possible. On
Wednesday, the cold front will finally slide to the east into and
across the area. It may still get hot as some models are slower
the frontal passage. A lot of uncertainty in the potential for
severe thunderstorms due to the frontal position, cloud cover and
ongoing showers and storms Wednesday morning. Beyond Wednesday,
the ECMWF has the frontal boundary meandering across the northern
United States, resulting in additional chances of storms. It is
too early determine if any of these storms would become severe.
Temperatures by the end of the work week should return closer to
normal.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 644 AM CDT Sun Jun 16 2024

Showers and scattered thunderstorms will move through the region
through late morning or early afternoon, and storms with
associated MVFR/IFR conditions are possible at all TAF sites.
Later in the day, the rain chances lower considerably as the
atmosphere gets capped. A cold front will push into NC WI tonight,
and may provide enough lift to generate some storms, especially
at the RHI TAF site. Low ceilings are expected to develop on the
cool side of the boundary, as it gradually sags southeast during
the overnight hours.

LLWS will continue for a few hours this morning. Otherwise, gusty
SE winds will become S-SW as a warm front lifts north across the
region this afternoon. Gustiness will subside after sunset
tonight.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through late tonight for WIZ022-040-050.
&&

$$

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