327
FXUS63 KMQT 241743
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
143 PM EDT Mon Jun 24 2024

.KEY MESSAGES...

- Line of thunderstorms moves through the forecast area tonight,
  some storms could be strong to severe and produce damaging
  winds and large hail.

- Tuesday will be the warmest day of the week with highs in the
  mid 70s to mid 80s. Gusty winds to 30 mph also expected,
  especially over the Keweenaw.

- Next round of precipitation expected Thursday night into the weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 143 PM EDT Mon Jun 24 2024

Current mesoanalysis across the region places an upstream shortwave
moving through northern Minnesota and a cold front tied to a surface
low moving through Lake Winnipeg not far behind. Precip associated
with this is trending down per DLH radar and GOES IR. To the south,
mid-level ridging extends across the Plains with subtle shortwaves
perturbations embedded atop. At the surface, a surface low was
observed moving across eastern South Dakota along with a
southeastward draped warm front and several surface troughs tied to
the mid-level perturbations. Across our forecast area, surface high
has allowed for clear skies to largely dominate; at the time of this
publishing though, high clouds streaming eastward into the region
associated with the shortwave pressing through Minnesota was
observed on GOES Vis imagery. With these mostly clear skies and
predominately southerly flow, daytime temps have warmed into the 70s
while dewpoints in the 50s have been observed.

As we progress through the remainder of the afternoon and overnight
tonight, upstream weakening showers in Minnesota will continue to
weaken as it presses into Lake Superior/western Upper Michigan. HRRR
and other CAMS suggest it may hold together enough to support some
showers in our forecast area late this afternoon/early evening.
Otherwise, expect temps to continue climbing into the upper 70s to
low 80s and increasing cloud cover.

Impressive instability will continue building on the south side of
the decaying shower activity over Minnesota. As this area of
instability grows and southwesterly low level winds strengthen this
evening, a line of thunderstorms will develop over central
Minnesota. These will grow upscale and evolve into a bowing MCS as
they stream southeast along the instability gradient. CAMS appear to
be coming into better agreement that the strongest storms will stay
south of our forecast area, but storms capable of mostly damaging
winds can`t be ruled out early in the event. Some large hail will
also be possible. The main risk area will be in the counties
bordering Wisconsin. North of this bowing segment, the HRRR and to
some degree, the FV3 and NAMNEST resolve a secondary line of showers
and thunderstorms across the Arrowhead into Ontario, then press
these into Lake Superior and Upper Michigan. Some large hail and
maybe strong winds will be possible with these storms if the
materialize, but confidence in these developing is low to medium (25-
50%) given their proximity to the main bowing segment and the lack
of a consensus among the various CAMS solutions. If this develop,
these and the northern fringes of the MCS pressing southeast, will
press eastward through Upper Michigan, likely clearing the east just
after sunrise. While confidence in the evolution is lacking
somewhat, consistent temporal signatures in the various CAMS suggest
the main period of thunderstorms to be between 5z and 11z with the
most likely period for strong to severe being early in the event.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 411 AM EDT Mon Jun 24 2024

Tuesday morning, a cold front draped from a 989mb low over far
northern Ontario and its parent 500mb trough will push through the
UP. While some thunderstorms will likely remain over some portions
of the UP, the extent that thundershowers remain is uncertain. Among
the 00Z HREF run, only the HRRR shows widespread thunderstorms
present by 12Z Tuesday with the other members showing only isolated
to scattered showers remaining. Attempted to somewhat split the gap
in these solutions with this forecast, but confidence is somewhat
low given the spread in the ensemble solutions. Any lingering storms
are unlikely to be severe as the better instability will be to the
south while better forcing will be to the north with probably less
than 1,000 J/kg of MUCAPE to work with over the UP. MOS guidance
suggests high temperatures in the central UP climbing to the mid 80s
with the 75th percentile of the NBM still hinting that 90s could be
possible in some typical warm spots in the south. Mixing behind the
front will allow for dew points to not be as high as originally
forecast. The other thing that mixing will do is create some gusty
conditions especially in the west and over the Keweenaw. This
forecast will reflect gusts in the 30-35 mph range, but the ceiling
for gusts over the Keweenaw could be higher as the HREF suggests
locally over 50% chances for 40 mph gusts Tuesday evening.

A dry period then is expected into Thursday night as a ~1015 mb high
pressure descends southeast through the Great Lakes from the
Canadian Prairie Provinces. While a shortwave trough will pass over
the UP Wednesday morning and both the Euro ensemble and GEFS show a
20-30% chance of precipitation, this forecast will reflect dry
weather with the subsidence associated with the dry weather. Cool
northerly surface flow on Wednesday will cause highs to only reach
the 60s, and potentially only the high 50s along the eastern Lake
Superior shores. Attention then turns upstream as a trough over the
Pacific NW makes landfall Wednesday night, then continues east along
the U.S./Canada border and reaches the Upper Great Lakes by
Saturday. This will support cyclogenesis in the northern Rockies
Thursday night/Friday with the low ejecting east-northeast to just
north of Lake Superior for Friday night/Saturday. While spread is
still high on the details of this system, the general trend is for
this low pressure to weaken as it approaches the Upper Great Lakes,
so hazardous weather seems unlikely at this forecast issuance. Drier
weather looks to return the rest of the weekend as a stronger high
pressure near 1025 mb settles over the UP by Sunday evening. As the
high shifts east to start next week, PoPs increase as another low is
expected somewhere in the Plains, but spread is high on the
track of said low.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 143 PM EDT Mon Jun 24 2024

VFR conditions will prevail this afternoon and evening, followed by
a rapid deterioration as a line of thunderstorms moves into Upper
Michigan. Expecting most activity between 5 and 11z, with the
greatest potential for severe winds, maybe some large hail, at KIWD
early on in the event. Expect ceilings to fall to MVFR/IFR after the
line moves through with some brief fog/mist developing before the
sunrise. Tuesday, gusty winds are expected to develop as ceilings
improve. Initial thoughts are KCMX could gust near 30kts from the
west, but some models indicate higher being possible.

&&

.MARINE...
Issued at 411 AM EDT Mon Jun 24 2024

Expect winds below 20 kts through the day as high pressure ridging
passes over Lake Superior. South winds increase to around 20 kts
tonight ahead of a passing cold front. Tuesday, gusty westerly to
northwesterly winds will increase to around 25 knots over the
western and central portions of the lake and to near 30 knots
between Isle Royale and the Keweenaw, with a 10% chance of a few
gale force gusts. Winds taper off Wednesday morning as they veer
north, remaining below 20 kts under high pressure through Thursday.
A weakening low pressure approaching the region will allow for gusts
near 20 kt, but given the uncertainty in the track of the low, the
timing and direction of these gusts is difficult to determine with
this forecast package. High pressure returns Sunday and ushers in
light winds.

Strong to severe storms are possible in the west tonight into
Tuesday with the passing cold front. Waves will be strongest north
of the Keweenaw Peninsula Tuesday afternoon and evening (4-6 feet).

&&

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

&&

$$

SHORT TERM...JTP
LONG TERM...GS
AVIATION...JTP
MARINE...GS