995
FXUS63 KMQT 021149
AFDMQT

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

.KEY MESSAGES...

-Two distinct rounds of precipitation today and tonight: one in
 the morning and one late at night. Thunderstorm chances are
 minimal with the first round and around 20%-30% with the second
 round.

-Widespread southerly wind gusts of 25-30 mph and as high as 40 mph
 across downslope areas today.

-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.

- Rain and thunderstorm chances continue this weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 445 AM EDT Tue Jul 2 2024

Current water vapor imagery/surface analysis early this morning
highlight a mid-upper level trough and its associated surface low
over southern Manitoba. And, latest radar mosaic is beginning to
light up across the far west as the first of two rounds of
precipitation enters Upper Michigan. Rain showers with the first
round will overspread the forecast area from west to east through
the morning.  But, with decent capping, it will be tough to get any
thunder this morning. By early afternoon, the western portions of
the forecast area will be in a bit of a lull, but a 40-50 kt low
level jet will contribute to gusty southerly winds as it passes
overhead.  Widespread wind gusts of 25-30 mph will be possible with
enough mixing to support upwards of 35-40 mph, especially across
downsloping areas.  Meanwhile, a second wave of showers with
thunderstorms this round will advance from the southwest and move
through Upper Michigan tonight with slightly better MUCAPE values to
work with.  Severe weather, however, is not expected.

&&

.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 /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 748 AM EDT Tue Jul 2 2024

VFR conditions will deteriorate to MVFR at all TAF sites by mid-
morning as rain overspreads Upper Michigan from west to east.  And,
further deterioration to IFR/LIFR is possible at IWD and SAW by this
afternoon. Other impacts include a low level wind shear threat
at both IWD and SAW through this afternoon and evening,
respectively. Strong southerly winds at the surface will also
gust up to 30 kts at IWD and SAW and up to 20 kts at CMX. Winds
will veer to the southwest late in the TAF period. Thunderstorm
threat is too low at this time to include mention, but cannot
entirely be ruled out at SAW later today/tonight.

&&

.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...
  Beach Hazards Statement through this evening for MIZ014.

Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...TDUD
LONG TERM...JTP
AVIATION...TDUD
MARINE...JTP