030
FXUS63 KGRB 131147
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
647 AM CDT Thu Jun 13 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

 - Showers and embedded storms will taper off over central and east
   central WI early this morning, and another round may occur
   south of Hwy 29 during the late morning and early afternoon.

 - Well above normal temperatures are forecast from Sunday into the
   middle of next week. Heat indices may surpass 90 degrees at
   times.

 - The next chance for widespread rainfall arrives Saturday night. It
   is uncertain if these storms would become severe, but locally
   heavy rainfall will be possible.

 - There are periodic chances of thunderstorms next week, although
   there is a lot of uncertainty in timing and location of the
   storms. With the building heat, stronger storms and locally
   heavy rainfall may be possible at times.

&&

.DISCUSSION...
Issued at 401 AM CDT Thu Jun 13 2024

Short Term...Today...Tonight...and Friday

An area of showers and embedded storms was moving through C/EC WI
early this morning. This activity was being sustained by moisture
convergence and WAA associated with a 35-40 knot WSW low-level
jet. This activity should continue to shift east and weaken
shortly after daybreak as the LLJ veers west and convection shifts
into a less unstable air mass. South winds gusting to 30 to 35
mph were occurring due to a wake low on the northern periphery of
the eroding stratiform precipitation shield. Farther west,
additional thunderstorms were developing in northern SD, in
association with mid-level frontogenetic forcing. A weak cold
front extended from western Lake Superior SWWD to SC MN. A moist
and marginally unstable air mass was present in advance of the
front, with MUCAPE of 400-800 j/kg and PWATs of 1-1.25 inches.

Thunderstorm Potential and Gusty Winds Today: Ongoing storms over
C/EC WI should shift south and east of the forecast area by 7 am,
followed by a short break in the activity. The previously-
mentioned mid-level frontogenetic forcing and the RRQ of an upper
jet should bring another area of showers and embedded storms to
areas south of Hwy 29 during the late morning/early afternoon.
CAPE is expected to increase to 1000-1500 j/kg by the time this
convection arrives, so a few strong storms with gusty winds and
small hail may occur. Otherwise, do not expect extensive
development as the weak cold front moves through, as westerly flow
at 925/850 mb will result in shallow/weak convergence. Later in
the day, short-wave energy will brush through northern WI, and
bring isolated to scattered light showers to areas near the WI/MI
border in the late afternoon and early evening. High temperatures
will be in the middle 70s to lower 80s. Lower humidity should be
noticed later in the day, in the wake of the cold frontal passage.

Deep mixing through 6-8k feet should tap into strong winds aloft,
resulting in west winds gusting to around 30 mph this afternoon.
Gusts should not be as strong over Lake Michigan, due to more
stable conditions over the relatively cool waters. Thus, expecting
gusts to remain below the 25 knot threshold for a Small Craft
Advisory.

Tonight/Friday: Canadian high pressure will bring mainly dry
conditions tonight into Friday, along with comfortable
temperatures and lower humidity. Lows tonight should range from
the upper 40s/lower 50s northwest to the 50s elsewhere. On
Friday, developing northeast winds and Canadian air mass will
result in highs in the lower to middle 70s, except mid to upper
60s lakeside.

Long Term...Friday Night Through Wednesday

The change in the 500mb pattern early next week will lead to the
potential first heat wave of the summer. The 00z models tonight
all indicate building 500mb ridge across the eastern United States
with developing 500mb trough over the western United States. The
ECMWF is most aggressive with the ridge building into the western
Great Lakes. The placement of the 500mb features will put us in
the ring of fire for much of next week. The differences in the
model solutions with the upper air features and the placement of
convective systems can be seen in the model guidance, especially
the surface features and the Qualitative Precipitation Forecast
(QPF). The ECMWF/Canadian model are considerably warmer than the
GFS, and this shows up on the numerical guidance values for
highs/lows based off the GFS/ECMWF models.

For Friday night, it will be cool across the north with several
locations falling into the middle to upper 40s. On Saturday,
temperatures will rebound into the 70s as clouds will be on the
increase during the day. There are still timing difference when
the rain will arrive, but looking at mid to late afternoon across
our western counties. On Saturday night, the low level jet cranks
up to near 40 knots with plenty of moisture flowing northward.
Elevated instability will lead to the increasing chances of
thunderstorms during the evening across our western counties, then
across the entire area overnight. Locally heavy rainfall is the
main concern, although some stronger storms are possible with
gusty winds and hail as 0-6km shear values increase to 30 to 35
knots. The greatest risk of stronger storms would be across
central into east-central Wisconsin. Sunday continue to be
problematic with respect to high temperatures. Ongoing convection
and cloud cover linger through much of the morning with some
partial clearing possible in the late morning and afternoon.
Additional convection may redevelop during the afternoon. Have
trended lower on high temperatures on this day due to the
continued persistence of the convection and expected cloud cover.

For Monday, the Canadian and ECMWF model push the front into
northern Wisconsin which would allow temperatures to climb well
into the 80s and lower 90s across central and east-central
Wisconsin with the afternoon heat index values climbing into the
lower to middle 90s. The GFS model solution has the front south of
the area with convection along it. From Monday through Wednesday,
will need to worry about the ring of fire as thunderstorm
complexes are expected at times that would move across the Upper
Midwest and western Great Lakes. These features can produce
outflow boundaries and push the front southward that could mess up
the high temperature forecast at times, with cooler readings than
expected. The forecast high temperatures from Monday through
Wednesday are a blend of the warmer ECMWF numerical guidance and
the cooler GFS guidance. The Canadian model would support the
warmer ECMWF guidance values.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 638 AM CDT Thu Jun 13 2024

Showers and embedded thunderstorms over SW MN will shift east and
impact areas south of Hwy 29 during the late morning and early
afternoon. Additional light showers will be possible near the
WI/MI border during the late afternoon and early evening.
Otherwise, expect VFR conditions to prevail through the TAF
period.

Gusty west winds to 25 kts are expected at the TAF sites this
afternoon.

&&

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

&&

$$

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