743
FXUS63 KMQT 231141
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
741 AM EDT Sun Jun 23 2024

.KEY MESSAGES...

-Rain tapering off this morning, but more showers and storms
possible this afternoon.

-Moderate swim risk today for Marquette and Alger county Lake
Superior beaches.

-A slight risk (~15%) of damaging wind and hail in the west
associated with thunderstorms Monday night into Tuesday morning.

-Tuesday will be the warmest day of the week with highs in the mid
80s, with dew points in the 60s making it a hot and muggy day.

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

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 516 AM EDT Sun Jun 23 2024

Latest water vapor imagery shows one shortwave moving across the
Upper Great Lakes early this morning with another shortwave/closed
low poised upstream over southern Manitoba. The shortwave now over
the Upper Great Lakes and its associated sfc low are in the process
of exiting the area to the east. Showers in the
wraparound/deformation area of the shortwave have weakened
substantially in the last couple hours as noted on radar imagery and
the warming cloud tops on IR satellite imagery with only light
scattered -shra into central and eastern portions of the cwa.
Expect these light showers to exit east later this morning.
Dense fog has ended and only patchy fog remains so have cancelled
the Dense Fog Advisory for Marquette and Alger counties.

Attention then turns to the closed low/vort max now upstream over
southern Manitoba which will move over the Upper Great Lakes as an
open wave this afternoon and early evening. A buildup of 200-400
j/kg of skinny CAPE as this shortwave moves across the area will
lead to scattered showers and isolated t-storms this afternoon which
will die out over south central Upper Mi early this evening. Cooler
and somewhat breezy northwest winds off Lake Superior in the wake of
the system moving east of the area this morning will limit the
buildup of afternoon instability while also leading to a moderate
swim risk today for the Lake Superior beaches of Marquette and Alger
counties. Expect highs ranging from the lower to mid 60s north along
Lake Superior to the lower to mid 70s south central under a mix of
clouds and sun.

After any lingering convection dies off early this evening south
central, a high pressure ridge building over the area from the west
will lead to clearing skies and light winds. NAM soundings suggest
the possibility of shallow patchy fog forming overnight over the
interior. Look for lows ranging from the mid to upper 40s over the
interior to the lower to mid 50s along the Great Lakes shores.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 442 AM EDT Sun Jun 23 2024

Beginning this coming week, persistent 500mb ridging over the
southwest to south-central US with longwave troughing over the
eastern coasts of North America leaves the Upper Great Lakes in the
main path of shortwaves riding above the ridge and into the larger
trough. The resulting surface features will result in multiple
distinct rounds of rainfall in this period, first Monday night
through Tuesday and then again late Thursday into the weekend. The
best chances (~15%) for strong thunderstorms will be with the
precipitation Monday night into Tuesday. Without long-duration
southerly flow, temperatures generally remain near-seasonal, with
the exception of Tuesday when temperatures look to climb to around
80 with dew points in the 60s.

Once the remaining fog burns off in the early morning hours, Monday
looks to be a mainly quiet day as the region is on the north side of
a 1015mb high pressure. CAMs resolve a lake breeze along Lake
Superior, but otherwise, southerly to southwesterly winds begin to
build in response to a deepening low pressure near 990mb transiting
central Saskatchewan and Manitoba. The warmer, moisture-rich air
will allow instability to build late, with both GEFS and Euro
ensemble CAPE probabilities of over 1k J/kg well over 50% for much
of the interior western and central UP by Monday night and 30-40%
chance of 2k J/kg. The mainly southerly surface flow contrasted with
the mainly westerly flow aloft will create a supportive shear
profile for the maintenance of storms, as surface-500mb shear values
will be near 40 kt in the west Monday night. The forcing will come
from the cold front draped from the low as it passes into far
northern Ontario. With the past 24 hours of model guidance,
confidence has increased in the cold front arriving in the western
UP around 06Z Tuesday. The current run of the HREF shows virtually
no precipitation potential prior to 00Z over the UP, however, it
does show convective initiation further upstream, and given the
present forcing and ingredients present, the SPC Slight Risk for
dual 15% risks of severe wind and hail is warranted. The biggest
source of uncertainty seems to be in storm mode, whether it will
maintain a (super)cellular structure or if a MCS will form upstream.

Southerly winds at the surface persist into the daytime hours
Tuesday, which the warm advection combined with radiational heating
will allow Tuesday to be the warmest day of the week, with the most
likely high temperatures for Tuesday being in the low to mid 80s,
though the 75th percentile shows some isolated spots of 90s. It
could also be a muggy day as forecast dew points approach 70.
Eventually, winds will veer westerly behind the front draped from
the long-away low pressure and temperatures will moderate somewhat.
Lingering thunderstorms are possible, especially if the lifting from
the front is on the stronger end of guidance, but PoPs are generally
expected to be around 30% Tuesday afternoon to evening.

Ensemble guidance has increased in certainty over the past 24 hours
in a high pressure following behind the cold front, transiting the
Upper Midwest and through the Great Lakes Wednesday through Thursday
morning. This will lead to the most prolonged dry period of the
forecast period with generally clear skies and light winds forecast.
Meanwhile, a deep 500mb trough will make landfall in the
Seattle/Vancouver region, setting up another northern Rockies low
pressure forming by Thursday evening. PoPs over the UP gradually
climb as this low will most likely eject towards and north of the
Great Lakes by Friday and the weekend. Exact timing, location, and
intensity of showers is still hard to pin down given the growing
range of possibilities, but there is a surprising amount of
certainty in the next high pressure bringing dry weather to the
region by next Sunday. Overall, nothing in the ensembles shows any
major shift in the pattern, which lines up with the CPC continuing
to outlook the UP with best chances for above average temperature
and precipitation even into the first portions of July.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 732 AM EDT Sun Jun 23 2024

Conditions have improved early this morning as showers have
tapered off. IWD and CMX are now VFR and SAW is MVFR. SAW should
improve to VFR later this morning. Another disturbance from
Manitoba will move in this afternoon triggering more scattered
showers and possibly a thunderstorm. SAW will probably have the
best chance of any of the terminals for getting showers, but
given weak instability there is plenty of uncertainty on shower
coverage so only have included VCSH in the TAF. Light winds
under clearing skies could lead to patchy fog late tonight at
some of the terminals, particularly at IWD and SAW where MVFR to
IFR vsbys are expected.

&&

.MARINE...
Issued at 442 AM EDT Sun Jun 23 2024

A low pressure system will exit into Ontario this morning.
Today, west to northwest winds will mainly remain below 20 kts. High
pressure ridging then passes over Lake Superior tonight and Monday,
keeping light winds in the forecast until Monday night. South winds
increase to around 20 kts Monday night ahead of a passing cold
front. Southwest winds behind the front are expected around 20-25
kts, though a few gusts may be in the 25-30 kt range between Isle
Royale and the Keweenaw Peninsula Tuesday afternoon. Winds taper off
Tuesday night into Wednesday, remaining below 20 kts through the
late part of the week.

Some isolated thunderstorms are possible this afternoon and evening
across the west. Strong to severe storms are possible in the west
Monday night into Tuesday with the passing cold front. Waves will be
strongest between Isle Royale and 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