374
FXUS63 KMQT 290713
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
313 AM EDT Sat Jun 29 2024

.KEY MESSAGES...

- Strong to potentially severe storms, capable of large hail and
damaging winds, could develop today across the east half of Upper
Michigan.

- Rip currents and dangerous swimming conditions will be possible at
Lake Michigan beaches of Schoolcraft County this morning.

- Rip currents and dangerous swimming conditions will be possible at
Lake Superior beaches of Alger and Marquette counties
this afternoon and evening.

- Dry weather Sunday morning through Monday evening under high
pressure.

- Next rounds of showers and thunderstorms arrive Monday night
through Tuesday night.

- Warm and wet pattern expected to continue well into July.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 312 AM EDT Sat Jun 29 2024

A rich theta-e airmass across the eastern half of the forecast area
has resulted in a few waves of rain showers with some observed
lighting here and there. This, while the west has been under the
influence of a weak surface low positioned over western Lake
Superior per MSAS analysis. Further upstream, mid-level trough
moving through western Minnesota has supported convection across
central Minnesota ahead of a surface cold front pressing eastward.
Mild and moist conditions, in addition to some pockets of fog, have
also been observed under mostly cloudy skies.

The mid-level shortwave in Minnesota will force the surface low in
western Lake Superior through the region and into Ontario while it
pulls behind the trailing cold front. Showers with some
thunderstorms should develop ahead of the boundary as it shifts east
through the region. Deterministic packages suggest instability could
grow to 500-1000j/kg MLCAPE under 50+kts of deep layer shear.
Primary spots for this environment will be central, south, and
eastern portions of the forecast area by early/mid afternoon. This
environment could support some strong to severe storms. Primary
hazards would be large hail and damaging winds if they do develop.
Behind the front in the west, winds become onshore and, with the
additional upslope component and a continued saturated near surface
layer, light rain and/or drizzle is expected to develop. Ahead of
the front in the south and east, expect temps to climb into the mid-
upper 70s to low 80s while frontal passage should limit heating to
the low 70s in the west and 60s Keweenaw.

Strong pre frontal southerly winds are expected for Lake Michigan
beaches of Schoolcraft County this morning and strong post frontal
northwesterly winds should follow with the frontal passage. These
are expected to create dangerous swimming conditions for Marquette
and Alger counties this afternoon/evening. Beach hazard statements
have been issued for both.

&&

.LONG TERM /TONIGHT THROUGH FRIDAY/...
Issued at 312 AM EDT Sat Jun 29 2024

Tonight, as the main axis of the 500mb trough passes east beyond the
UP, a backdoor impulse in the northwesterly flow combined with
upslope flow creates just enough lift for the 00Z HREF to show an
orographic pattern of light rain showers overnight. Efficient mixing
will also allow for some gusty winds over the eastern UP to 20-30
mph overnight.

Any lingering showers will not survive to 12Z Sunday morning however
as advancing 500mb ridging aloft will support a surface high
pressure of near 1028 mb to traverse from Minnesota Sunday morning
to southern Ontario by Monday night. This high will usher in a
period of dry weather and mainly clear skies Sunday through Monday
afternoon. With the near-surface flow being mainly northwesterly on
Sunday with the high still to the west, temperatures near Lake
Superior may struggle to break out of the 50s, but otherwise
temperatures across the UP will only be slightly below normal.
Efficient radiational cooling overnight into Monday will help low
temperatures to fall to near or just below 40 in some interior
locations per some MOS guidance and the NBM 25th percentile and
below. There is also some potential for some patchy fog in the south-
central, with Euro ensemble meteograms showing a 25-30% chance
of lowered visibility in Menominee Monday morning, though
similar signals were not found in Iron Mountain to the northwest
or Rapid River to the northeast. However, despite the
relatively low probabilities, every Euro ensemble member that
shows fog, the fog is below 1/2 mile, so the fog forecast bears
some watching.

Attention then turns upstream to 500mb troughing lifting out of the
northern CONUS Rockies Monday evening. This will form a 990s mb
surface low that will pass from southern Saskatchewan Monday
afternoon to far-northern Ontario Tuesday night. Ahead of the low,
building southerly surface flow will cause warm advection and
isentropic upglide which in turn will create showers well ahead of
the fronts associated with the low pressure. Ensembles still lack
consensus on whether there will be enough separation in the initial
wave of showers and the frontal showers to create a period of dry
weather, but the NBM is leaning towards keeping PoPs in the 60-80
range all through Monday night through Tuesday night. Despite nearly
24 hours of elevated PoPs, the probabilities of flooding rainfall
are below 10%. With the strongest dynamics of the system well to the
north, severe weather is not expected, though the Euro ensemble
shows up to a 50% chance of 500-1000 J/kg of CAPE by Tuesday night,
so thunderstorms will remain a possibility with this system. After
this system exits by Wednesday morning, model guidance really begins
to diverge. A dry period is expected to follow, but how long that
period lasts is still uncertain. Generally a wetter pattern
continues into through the first half of July.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 122 AM EDT Sat Jun 29 2024

Flight restrictions to persist for duration of TAF period as showers
and isolated thunderstorms form to the south along a cold front
early this morning. A brief period of VFR at IWD should deteriorate
to MVFR over the next few hours, and the MVFR conditions currently
at CMX will fall to IFR/LIFR. Elsewhere, the most persistent LIFR
conditions through the early morning will be at SAW due to upsloping
southerly winds. Improvement is expected, though, later this morning
with frontal passage. For now, will only carry VCSH mention at IWD
and CMX, but confidence in an uptick in convective activity is
higher at SAW in the Sat 08-11Z time.  So, will carry VCTS mention
there.  Otherwise, southerly wind gusts have tapered off over the
last few hours and the only other wind impact will be a wind shift
to the northwest in wake of cold front later today.

&&

.MARINE...
Issued at 312 AM EDT Sat Jun 29 2024

Westerly wind gusts below 20 knots are ongoing this morning, though
as winds veer northeasterly this afternoon, increased mixing and a
tighter pressure gradient allowing for gusts up to 25-30 kts over
the eastern half of the lake. A few gusts may (~25% chance) reach
gale force strength around 8PM EDT tonight between Stannard Rock and
the Pictured Rocks National Lakeshore. North to northeast winds
Saturday night gradually fall back below 20 kts by Sunday morning as
high pressure builds in from the west. Winds are then expected to
remain below 20 kts through much of the day Monday as this high
pressure moves east over the lake. With the next passing system
early next week, southeast winds increase Monday night to 20-25 kts,
veering south-southeast on Tuesday as the low pressure system passes
well to the north of Lake Superior. Besides a brief period Wednesday
of southwesterlies gusting to 20-25 kts, winds Tuesday night onward
look to remain below 20 kts through the remainder of the forecast
period.

Stronger northwest winds behind the cold front this evening will
result in waves building up to 6-9 ft waves over the eastern half of
the lake Saturday night, falling below 4 feet by Sunday morning.
Sustained southeasterlies Tuesday will allow waves to grow to 4-6
feet along the US/Canada border on Lake Superior through Tuesday
night.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Beach Hazards Statement from this afternoon through this
     evening for MIZ005-006.

  Beach Hazards Statement until 10 AM EDT this morning for
     MIZ014.

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

&&

$$

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