210
FXUS63 KMQT 241140
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
740 AM EDT Mon Jun 24 2024

.KEY MESSAGES...

- Convection develops tonight along incoming Plains cold front
  with the potential of strong to possibly severe storms,
  although there is a great deal of model uncertainty on the
  evolution and coverage of the convection across the U.P.

- 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 533 AM EDT Mon Jun 24 2024

A surface high pressure ridge building over the area has yielded
mostly clear skies across Upper Mi early this morning. Light winds
and relatively moist dew points around 50F to the lower 50s has also
resulted in some patchy fog at a few locations, especially along the
WI border over the interior west half.

Surface high pressure will persist during the day on Monday
resulting in mostly sunny skies through much of the day. There will
be a slight increase in mid and high clouds late in the day over the
west in advance of a cold front approaching from the Plains. Under a
developing WAA southerly flow, model guidance has high temperatures
reaching near 80F across much of the interior, maybe even a few
degrees warmer for west half downsloping locations along Lake
Superior. The southerly flow will keep temps cooler along Lake
Michigan where lower to mid 70s readings will be more common.

Attention tonight turns to a shortwave riding east across Manitoba
and northern Ontario which will send an associated cold front east
into Upper Mi late tonight. CAMs show convection developing along
this front, but are in poor agreement with exactly how this
convection evolves and how much of it tracks across Upper Mi late
tonight. Several of the models hint at the stronger convection in
the form of a linear MCS diving south of Upper Mi through WI
following the gradient of juicier dew points (in the lower 70s) and
higher theta-e air. These models also show another cluster of
stronger storms lifting north over Lake Superior following closer to
the track of the shortwave and the best dynamic forcing with the
system. In effect, these scenarios would have the best convection
splitting north and south of the area with only scattered showers
and isolated t-storms at best impacting the U.P. Impressive mid-
level subsidence and capping with 18c or warmer air between 850 and
800 mb as noted off latest NAM and RAP soundings would also argue
for a drier solution over Upper Mi later tonight. Following this
reasoning decided to cut back PoPs from the likely to categorical
PoPs depicted by the NBM to just chance for now. If (and this is a
BIG if) convection can somehow break through the impressive cap over
the area veering wind profiles and 1000-2000 j/kg MUCAPE could lead
to the development of supercells and a large hail/wind threat
clipping areas of the cwa, especially along the WI border. Min temps
tonight will range from the upper 50s east to lower to mid 60s
elsewhere.

&&

.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 /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 735 AM EDT Mon Jun 24 2024

VFR conditions are expected today under high pressure. The
approach of a cold front from the west will bring in a threat of
showers/t-storms into the western U.P. later this evening.
While there is considerable model uncertainty at this time on
the evolution of these showers and possible storms tonight, I
did include VCSH for IWD and CMX by late evening/overnight into
Tue. A tightening pressure gradient ahead of the front will
also result in LLWS at all the terminals tonight.

&&

.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...Voss
LONG TERM...GS
AVIATION...Voss
MARINE...GS