100
FXUS63 KMQT 292018
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
418 PM EDT Sat Jun 29 2024

.KEY MESSAGES...

- Thunderstorms continue across the far eastern UP through the early
evening; some storms may be strong to severe with large hail and
gusty, damaging winds.

- Rip currents and dangerous swimming conditions will be possible at
Lake Superior beaches of Alger and Marquette counties through this
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 SUNDAY NIGHT/...
Issued at 418 PM EDT Sat Jun 29 2024

Thunderstorms continue across the far eastern UP this afternoon,
with a cold front not far behind in the central UP. These storms
have a history of producing large hail, and with MUCAPE still up to
2000 j/kg and sufficient shear to sustain updrafts, will not rule out
additional strong convection from eastern Luce county southwest
through Green Bay. Meanwhile, outflow from earlier storms in
northern Marquette and Alger counties is quite apparent on radar,
and has touched off additional weak showers. That said, most
convection apart from clusters currently working through Luce,
southern Schoolcraft, and Mackinac counties have struggled to climb
high enough even to produce lightning - not surprising, given modest
capping indicated in model soundings and the afternoon NUCAPs
profiles.

Upstream, additional spotty shower activity has become apparent.
Given cooler post-frontal flow as winds turn over to the NNW, moist
lower levels, and another shortwave dropping from northern MN
through the UP tonight, expect spotty shower activity to continue at
least through the first half of the night. This would be most likely
across portions of the UP where NNW flow is upsloping (so, much of
the higher terrain of the western UP, portions of the north-central
UP, and across Alger and northern Luce counties). Skies gradually
clear out the rest of the night, with temperatures largely bottoming
out in the lower to mid 40s. However, some cooler spots in the
western and north-central UP may fall even further into the upper
30s.

Strong post frontal northwesterly winds are expected to create
dangerous swimming conditions for Marquette and Alger counties
through this evening. A Beach Hazards statement is in effect.

&&

.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 /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 129 PM EDT Sat Jun 29 2024

IFR ceilings prevail at CMX this afternoon, while IWD and SAW
continue to come in at VFR so far with just some thickening lower to
midlevel cumulus. Meanwhile, cold front is moving through the region
this afternoon, which should drop ceilings to MVFR at IWD over the
next couple of hours, the SAW follows by the early evening. Showers
and thunderstorms are already developing near SAW, and vcts will be
possible the rest of the afternoon before the front finally clears
the area. Post frontal upslope flow should enable additional showers
at KCMX and KIWD this evening before all terminals improve to MVFR
and finally VFR overnight.

&&

.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 until 10 PM EDT this evening for
     MIZ005-006.

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

&&

$$

SHORT TERM...LC
LONG TERM...GS
AVIATION...LC
MARINE...GS