600
FXUS63 KMQT 020733
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
333 AM EDT Tue Jul 2 2024

.KEY MESSAGES...

-Our next round of rain showers, with some rumbles of thunder,
 moves in by early Tuesday morning.

-Two distinct rounds of precipitation for Tuesday: one in the
 morning and one late at night. Thunderstorm chances are around
 20%- 30% for each round.

-Low chance (~25%) of afternoon and low to medium chance
 (25-40%) of evening showers/storms across Upper Michigan on
 Independence Day. Rain spreads over the region Thursday night
 and Friday.

-Weather pattern remains active into the second week of July.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 306 PM EDT Mon Jul 1 2024

The upper ridge axis is sliding across the Great Lakes this
afternoon, with surface high pressure centered over the Lower
Peninsula. With increasing southerly winds over the UP and a warmer
airmass working in, temperatures have been able to climb into the
70s across the UP; some spots in the western half of the UP, where
southerly winds are downsloping, are even flirting with the 80
degree mark.

Clouds will gradually spread in through the first half of the night
ahead of a shortwave that is currently ejecting out of the Plains.
Not far behind will be the next round of rain showers by Tue 06Z. As
the showers track eastward across the UP tonight, also cannot rule
out a few rumbles of thunder...but will note that instability
remains quite limited with capped soundings. Meanwhile, much warmer
lows can be expected tonight unlike the last few nights as the
clouds/rain limit radiational cooling. Widespread 50s will prevail
Tuesday morning.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 333 AM EDT Tue Jul 2 2024

There continues to be fairly good agreement among the deterministic
and ensemble packages in the extended period, supporting high
confidence in the overall progression of the pattern and the
features embedded within. Where confidence does shrink though, are
the details that come with the minor spatial and temporal
differences between these packages. Overall though, main item of
interest will be the period from late July 4th through the coming
weekend thanks to the eastward migration of negative height anomaly
through the Central Plains and central Canada.

Beginning Wednesday, mid-upper level closed low on the shores of
Hudson Bay will continue northeast, dragging behind a cold front
through the Upper Great Lakes. Most of the precip should clear the
eastern portions of the forecast area in the morning with surface
ridging and drier air building eastward into the region. A couple of
weak surface troughs looks to swing through through the day after
the main cold front exits. There`s a brief window where enough
destabilization could result in showers and thunderstorms developing
in the afternoon. MLCAPE among the various models generally averages
200-800j/kg with near 40kts of 0-6km deep layer shear. Models appear
to have expanded this risk area from yesterday`s eastern UP only, to
now isolated to scattered activity can`t be ruled out for a majority
of the forecast area. Another item of note will be the winds in the
west. While not incredibly strong, daytime mixing may support
westerly wind gusts near 20-25 mph for many locations. Along the
Spine and western lakeshores of the Keweenaw, wind gusts may
approach 35 mph at times. Conditions improve by evening as we
decouple. However, with a mild airmass overhead, overnight lows
should only dip into the mid-upper 50s in the interior and near 60F
by the lakeshores.

Ridging shifts eastward through the forecast area Thursday while
upstream, an amplifying shortwave/closed low exits the northern
Rockies and shifts eastward through the north-central Plains.
Guidance continues to suggest the system`s surface low will press
east through Minnesota and Wisconsin Thursday night and Friday, then
lift northeast through Upper Michigan Friday night into early
Saturday. The main forecasting challenge with this progression will
be the onset of precip on July 4th. Guidance continues to suggest
some afternoon destabilization alongside a weak inverted surface
trough could spark afternoon/evening convection. However, there is
the question of model run to run consistency and there are timing
and spatial differences in the parent low and thus, this inverted
trough. Overall though, it continues to look as those there is the
potential for afternoon and evening showers and thunderstorms across
the western half of Upper Michigan, and even as far east as
Manistique. Will opt to maintain NBM pops for this forecast cycle
given its representation of the low-end pop coverage increase and
overall 30-40 peak percentages across the west half of Upper
Michigan. If this does materialize, severe weather is not expected.
Regardless, anyone with evening outdoor/firework plans across the
western half of Upper Michigan should continue monitoring the
forecasts.

As the low presses closer overnight and into Friday, the timing and
spatial differences become more apparent, although 0z runs do appear
more aligned. A look at the GEFS and EC ensemble surface low
clustering highlights this well. But as the system shifts through
the region, any dry areas should fill in by Friday evening. The low
will exit into Ontario Saturday while another shortwave dips down
through Manitoba and western Ontario. At this point, its unclear if
this will result in another round of showers/storms to finish out
the weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 114 AM EDT Tue Jul 2 2024

VFR conditions prevail at the start of the TAF period with high
clouds increasing from the west. A strengthening pressure gradient
will keep southerly winds gusting to 20-25 kt for the rest of the
night at IWD/SAW. The southerly winds will eventually usher in more
moisture, allowing showers to spread across the terminals from west
to east through this morning. A 40-50 kt low level jet will result
in low level wind shear conditions developing shortly at IWD, and
slightly later this morning at CMX/SAW. Some of the stronger winds
will mix to the surface, with southerly wind gusts of 30 kt possible
for much of the day. MVFR cigs are expected to gradually develop
later this morning, persisting much of the day. There is around a
30% chance of IFR cigs developing at IWD/SAW during the day today,
but probs not high enough to keep prevailing in the TAFs at this
time. CMX/IWD expected to return to VFR around 00Z Thu, but cigs
remain lowered at SAW, with potential for IFR 00-06Z as well (though
still not high enough to include in the TAF).

&&

.MARINE...
Issued at 333 AM EDT Tue Jul 2 2024

Guidance continues to suggest strong southerly winds developing
today across eastern Lake Superior. The forcing for this is the
strengthening pressure gradient alongside a strong 40-50kt 925-850mb
low level jet moving along a mid-level shortwave lifting through the
region. Under the anticipated stable low level atmosphere, the
strongest winds should have difficulty mixing to the surface. With
this being said though, the pressure gradient, expected daytime
mixing over Upper Michigan, and terrain influences along Upper
Michigan`s lakeshore should be able to support areas where some
mixing should occur. Ensemble probabilities presented by the HREF,
NBM, and our internal probabilistic tools suggest the main risk area
for some low end gales will be along the lakeshores east of
Marquette, near Keweenaw Point, and north of Stannard Rock.
Probabilities among these are widely mixed though, presenting a
range of near 0 to 50% chance of 34kt winds at 10m, suggesting the
overall stable synoptic environment will have difficulty mixing. I
suspect higher observing platforms, such as Stannard Rock, will
observe these stronger winds this afternoon, but 10m observations
may only see the occasional gust. Given these persistent run to run
signals, the elevated nature of where the strongest winds will be,
and the localized nature of these stronger winds reaching the
surface, decided not to issue a gale warning.

Rain associated with this wave today may support some fog, mainly
across western Lake Superior where winds are expected to be lighter.
Winds should lighten this evening to 20kts or less as another round
of rain builds. The rain should persist into early Wednesday morning
as the system`s cold front presses west to east. Post frontal
southwesterly winds should be able to climb to 25-30kts across the
western half of Lake Superior, mainly between the Keweenaw and Isle
Royale by Wednesday afternoon. Winds lighten Wednesday evening, and
then are expected at or below 20kts going into the weekend. An
exception to this could be Friday if a surface low moving through
Wisconsin and Upper Michigan tracks a little further north than
current thinking. If this does occur, northeast winds in the western
half of Lake Superior may climb to near 25kts during the day.

&&

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

&&

$$

SHORT TERM...LC
LONG TERM...JTP
AVIATION...Thompson
MARINE...JTP