909
FXUS63 KGRB 070907
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
407 AM CDT Sun Jul 7 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Isolated strong thunderstorms are possible this afternoon/evening.
  Main threats with any stronger storms will be gusty winds and
  heavy rain. Severe weather is not currently 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.

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

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

&&

.DISCUSSION...
Issued at 406 AM CDT Sun Jul 7 2024

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

Thunderstorm coverage and strength through tonight main focus of
the short term.

WV loop shows broad mid to upper level trough is present from
south central Canada to the northern Plains. Within the trough
sharper shortwave is lifting into northern MN with additional
shortwaves crossing IA with some weak convection. At the surface,
weak low is over eastern ND while broad ridge is centered over
the Ohio Valley. As high departs and low approaches, elevated warm
front works across the region this morning. Isentropic ascent
along the boundary coupled with moisture advection is spurring
will continue to support broken band of showers and some rumbles
of thunder slowly pushing into western WI.

Today...Some of the remnants of these showers as well as the
other area of showers moving into far southwest WI will slowly
move into far west and southwest CWA by mid morning. Appears they
will weaken as they outrun higher MUCAPEs well to the southwest
since there is minimal low-level jet to carry the instability
farther east. Eventually by early afternoon, expect additional
showers and some thunderstorms to develop likely over north-
central WI and over southern WI ahead of another shortwave coming
out of IA. MLCAPEs forecast to reach 1000-1500J/kg (as temps reach
mid 70s to lower 80s) which will verify so long as the initial
mid-level clouds and any showers don`t dampen the instability too
much. That instability will be acted upon by modestly stronger
mid-level winds ahead of the trough which yields 30-35 kts of
effective shear. Greatest risk of an isolated stronger storm will
be over far north-central WI closer to the mid-level low and sfc
lows over northern MN. PWATS climb above 1.25 inches but warm
cloud depths well under 10kft are lower than recently. Corfidi
vectors do suggest storm motions could become slow, so could have
some heavy downpours. Gusty winds also possible, especially if we
realize the insolation and increasing CAPEs, steeper low-level
lapse rates. Mid-level lapse rates lacking at only 6c/km or less,
so don`t expect much chance for even small hail.

Tonight...After this potential for thunder impacts the area into
early evening, could be another round of showers and some thunder
overnight especially east-central WI where better low-level jet is
forecast to develop ahead of sfc low and approaching front. This
is also where corridor of highest PWATs (perhaps up to 1.80
inches) will be located. Some models and CAMS point to this idea,
but others keep showers and storms mostly to our east. HREF and
NBM probabilities for 6hr QPF are rather muted with <10 percent
chance of seeing over 0.50 inch during the overnight period. Thus,
will not play this potential up too much. If it did occur though,
main hazard would be heavy rain over east-central WI where soils
remain saturated and rivers remain high after recent heavy rainfall.
So, something to watch in a nowcasting sense.

Monday...Probably a general lull in wake of what occurs tonight
and as low-level jet gradually veers more WSW-W. Better chances
for showers and some thunder in the afternoon as primary front
arrives over central to north-central WI. Depending on extent of
instability building up in the afternoon (current indications are
at least pockets of MLCAPEs over 1000J/kg) could see some stronger
storms as mid-level jet is stronger and effective shear ramps up
to 40 kts. Stronger low-level jet will be aimed into MI but the
shear, instability balance and approaching front supports another
mention of gusty winds and heavy rain with stronger storms. Most
likely best chances for strongest storms would be ahead of the
front during peak heating from northeast to east-central WI.

Long Term...Monday Night Through Saturday

Not many changes to the extended. Focus continues to revolve
around on and off rain/storm chances through Wednesday as the
central CONUS remains under persistent troughing. Main forecast
concern will involve monitoring the track of Beryl and what
impacts it may have on the eastward progression of upper-level
ridging toward the middle of the week.

Monday evening through Tuesday... A combination of decent
moisture, daytime instability, and weak shortwave energy will
be enough to keep some pulse showers/storms in the forecast
through Tuesday. Coverage will likely be spotty given high
convective temperatures and lack of any real surface features.
Some stronger storms may be possible during peak heating, although
overall convective elements aren`t supportive of anything severe.
For this reason, locally heavy rainfall looks to be the main
threat with any stronger cells.

Rest of the extended... As has been previously advertised, a
warmer/drier pattern may be in the works for much of the Midwest
toward the end of the week. However, there are still some
questions as to how long this dry spell will last, especially as
the remnants of Beryl make their way up into the Great Lakes on
Wednesday. Most models currently suggest a northeast track
through Michigan`s lower peninsula as Beryl weakens and enters an
environment of prevailing westerly flow. However, any westward
shift would likely spell out additional rain chances for eastern
Wisconsin through the end of the week. Will continue to monitor
over the next few days.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1047 PM CDT Sat Jul 6 2024

Clear skies will give way to increasing middle clouds late tonight.
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 front will move across the region Sunday and could produce
some scattered showers or thunderstorms across central and north
central Wisconsin. A frontal system will bring showers and
thunderstorms to the area Sunday night and early Monday as it
moves slowly across the area.

&&

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

&&

$$

DISCUSSION.....JLA/Goodin
AVIATION.......RDM