821
FXUS63 KMQT 121844
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
244 PM EDT Wed Jun 12 2024

.KEY MESSAGES...

- Showers and thunderstorms expected (80% chance) between 9 pm
  and 3 am EDT tonight from west to east.

- There is a slight risk (category 2/5) of severe weather for
  the western UP, with the main threats being large hail in
  excess of an inch and damaging winds in excess of 60 mph.
  There is a marginal risk (category 1/5) elsewhere, except for
  the far east.

- Gusty winds expected Thursday along with lingering showers
  and thunderstorms.

- Dry Friday and early Saturday before the return of showers
  and thunderstorms later in the weekend.

- Warmer than normal temperatures frequent the forecast, with
  some areas approaching 90 for highs by next week.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 244 PM EDT Wed Jun 12 2024

Early afternoon water vapor shows a couple of low-amplitude
shortwaves embedded in fast midlevel flow over the north-central
CONUS. The first is generating lift and a couple areas of showers
along the WI/MI border and western Lake Superior, while an MCS is
ongoing further south into the better instability over southern MN.
No lightning strikes have been noted directly upstream as of yet,
and with HRRR trending a bit drier/less convective for this
afternoon, convection seems to be low probability and thus potential
for thunder was capped at slight chance (<25%) for the remainder of
the afternoon.

Of greater concern is the late evening/overnight period tonight.
Convection is expected to develop rapidly over northern MN this
afternoon as steep (> 8C/km) lapse rates overspread the area. A
classic loaded gun sounding in this area should yield intense storms
assuming that forcing from the second aforementioned low-amplitude
wave and attendant low-level boundary is sufficient, which it should
be. The question for our area is to what extent these storms will
hold together as they cross Lake Superior. The steep midlevel lapse
rates should maintain MUCAPE of 1000-1500 J/kg across the western UP
as the storms arrive. Wind shear is quite impressive both in the low
levels, with a low-level jet of 30-40 kt overspreading the area, and
in terms of deep-layer bulk shear which will max out between 40-60
kt. CAMs vary in their depiction of the incoming convection, but the
HRRR has been relatively consistent in maintaining a broken line of
organized strong/severe storms across the lake. Large hail in excess
of an inch is a threat given the strong shear and steep midlevel
lapse rates, and damaging winds in excess of 60 mph are also a
threat despite the nocturnal period given the strong low-level wind
field and likely maintenance of a respectable low-level mixed layer
as well. SPC slight risk (level 2/5) in effect over the western
counties. Storms should weaken with eastward extent as they outrun
the better midlevel lapse rates and instability, but at least
isolated strong/severe storm threat exists across most of the UP as
SPC Marginal Risk (level 1/5) covers all areas except the eastern
quarter or so. Main timeframe for storms looks to be roughly 01-06Z
from west to east (9 pm-2 am EDT).

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
Issued at 553 AM EDT Wed Jun 12 2024

The extended period will immediately start out this evening in the
middle of a convective event as the first of two shortwaves
continues its progression across the region.  The question of
intensity, though, still remains the biggest challenge.  With decent
0-6 km shear values near 50 kts, thunderstorms will have a chance to
maintain some strong to severe potential.  But, the limiting factor
in the Thu 00-06Z time frame remains instability.  With MUCAPE
values in the 250-500 J/kg range and CIN values well below -50 J/kg,
storms will most likely diminish as they track across Upper Michigan
into tonight with just some rumbles of thunder and lingering rain
over the eastern third by Thu 09-12Z.

Thursday, after the early morning round of showers/thunderstorms, it
will generally be quiet through the morning. Nonetheless, strong
west-northwest winds will follow in the wake of the associated cold
front.  And, then a few showers/thunderstorms could develop again
during Thursday afternoon as the next shortwave provides a bit of
lift during the best diurnal heating of the day.  Severe weather
isn`t expected, but cannot entirely rule out a few strong ones with
some gusty winds and small hail.  The main impact Thursday will be
the winds outside of any storms, which will be strong as they mix
down behind the aforementioned cold front. Widespread 25 to 30 mph
winds are expected with isolated gusts in excess of 35+ mph per
GFS/ECMWF ensemble means.

After the winds diminish and rain tapers off Thursday evening, there
will be a period of benign weather through Saturday morning due to
ridging aloft. With the calmer weather will be slightly cooler, but
still above normal temperatures in the 70s before the start of
another warming trend through the weekend as guidance continues to
trend toward mid to upper 80s Monday through Wednesday.  Along with
the heat, though, will be multiple chances for showers and
thunderstorms starting Saturday morning as the next surface low
approaches from the southwest.  This low will track across the
region over the weekend quickly followed by a broad upper low.
Details with timing and strength remain low at this point, but
the main consensus is a trend toward another hot period with
active weather.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 144 PM EDT Wed Jun 12 2024

Main aviation concerns include timing and strength of potential
thunderstorms, potential for low clouds following the storms at CMX,
and low-level wind shear potential. There are two potential windows
for thunderstorms. The first is roughly 18-22Z at CMX and 20-24Z at
SAW. So far, no upstream convection is noted, and although modest
destabilization is occurring, potential for the first round is too
low to warrant inclusion in the TAFs. The second and more likely
round is roughly 01-04Z at CMX/IWD and 03-05Z at SAW. Storms in this
timeframe could produce strong wind gusts in excess of 40 kt as well
as large hail to around an inch at CMX/IWD. Storms will be weakening
with eastward extent but brief gusty winds and small hail still
could occur at SAW. Vsby could fall to IFR/MVFR in any storms. After
the storms, cloud bases will likely lower to MVFR/IFR late tonight
at CMX before rising/scattering by around 12Z Thu. Low-level wind
shear will be a concern at all sites tonight as a strong
southwesterly low level jet moves overhead. Outside of storms and
the period of possible low clouds at CMX, VFR conditions are
expected.

&&

.MARINE...
Issued at 454 AM EDT Wed Jun 12 2024

Southerly winds mainly 20 knots and lower will persist across Lake
Superior into this afternoon. But, as the high pressure is replaced
by a series of disturbances, an uptick in southerly winds of 20 to
25 knots can be expected late this afternoon. In addition, rain and
general thunderstorms will be possible across the far western
portions of the lake by late morning, overspreading the remainder of
the lake by this afternoon. Some storms could become strong to
severe, though, late this afternoon/evening mainly over the far
western portions of Lake Superior. Thursday, winds will become west-
northwesterly behind a cold front with 20 to 25 knots (isolated to
30 knots) outside of any additional thunderstorm chances through the
day. By Friday, winds will return to less than 20 knots with the
return of high pressure where they will stay until early Sunday
morning.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...Thompson
LONG TERM...TDUD
AVIATION...Thompson
MARINE...TDUD