604
FXUS63 KMQT 040033
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
833 PM EDT Mon Jun 3 2024

.KEY MESSAGES...

- Showers and a few thunderstorms progress eastward across west
  and central Upper MI today. Greatest coverage will be over the
  west. Severe storms not expected.
- Frequent opportunities for showers and thunderstorms over the
  next 7 days, with a break on Tuesday.
- Above normal temperatures through Wednesday, then turning
  cooler for the second half of the week.

&&

.SHORT TERM /THROUGH TODAY/...
Issued at 141 PM EDT Mon Jun 3 2024

RAP analysis shows a 500mb shortwave over Minnesota generally
flattening with time this morning and early afternoon. This
correlates with the decrease in rain shower intensity with a
broad line of showers over the central UP at 15Z per KMQT radar
reflectivity and METAR obs. CAMs consistently show this
deteriorating trend continuing as forcing continues to decrease
and precipitation battles dry air. However, a break in the
showers altogether will be brief at most as a shortwave over
Iowa will progress northeast throughout the day today and force
another round of showers through central to northern Wisconsin
by 20Z today. The main source of uncertainty is the northern
extent of the showers and thunderstorms, as cloudy conditions
associated with the current shortwave are limiting the ability
of the atmosphere over Upper Michigan to destabilize. The 12Z
HREF shows some SBCAPE recovery in the west, but with forcing
being limited to the south and central UP, where even HREF max
SBCAPE struggles to reach 250 J/kg, severe weather is not
expected, and thunder chances are limited to below 33%. As far
as high temperatures go, clearing behind the showers in the west
and the persisting dry air over the east will make the west and
the east ends warm into the low 70s today while the central UP
stays in the 60s.

Overnight, as heating decreases, so too will shower coverage, with
HREF probabilities of hourly QPF > 0.01" not exceeding 40% after 03Z
tonight. Persistent cloud cover and a more moist surface airmass
will limit radiational cooling, with lows around the mid 50s and low
60s tonight. In the wake of showers, marine dense fog over Lake
Superior is 60%+ likely per the HREF, with the central UP seeing
30-60% chances to see patchy dense fog overnight. With the wide
range of probabilities, no land-based dense fog advisories are
going to be issued with this forecast package until a bit more
certainty is gained in regards to the moistening of the
atmosphere by the showers.

&&

.LONG TERM /TUESDAY THROUGH MONDAY/...
Issued at 404 PM EDT Mon Jun 3 2024

Another subtle shortwave moving through the Great Lakes will keep a
potential for a few sprinkles, light rain showers, and a few rumbles
of thunder across the eastern UP into Tuesday morning. Otherwise,
with plenty of lower level moisture behind today`s rain showers and
partially clearing skies behind the front, much of the UP should
be starting off with some patchy fog. This mixes out soon after
sunrise with our high sun angles, then a brief dry period is
expected until late afternoon over the far west at the very
earliest as a second, stronger cold front approaches from the
Northern Plains. With warm air advection continuing ahead of the
cold front, expect the warmest temperatures of the week to
occur Tuesday, with highs getting into the 80s across some of
the interior areas, particularly over the west and downslope
areas near Lake Superior where the increasing southerly
downslope winds throughout the day could locally increase
temperatures by at least a few degrees; the warmest temperatures
will likely be around Ontonagon to the Porcupine Mountains. In
addition to the warm temperatures, Tuesday may also feel pretty
muggy, with much of the guidance showing dewpoints in the lower
to mid 60s across the UP.

The cold front looks to begin bringing showers and thunderstorms to
the western UP Tuesday evening, though guidance is hinting at some
earlier convection during hte late afternoon courtesy of a pre-
frontal trough rippling through. With quite an unstable airmass
(SBCAPE in excess of 1000j/kg) and an inverted-v type sounding, any
stronger cells that can get going could bring down some marginally-
severe winds or hail. That said, bulk shear remains lackluster even
as the cold front approaches, with values generally less than 30
knots likely not enough to sustain a severe threat much further
eastward into the UP. What may be more of a concern is the threat
for heavy rainfall, with ensembles generally showing PWATS around and
even in excess of 1.5in. Soundings show plenty of deep moisture and
impressive warm cloud depths, with storm motion largely parallel to
the cold front. Training could be a problem, particularly throughout
the western UP where we were able to pick up on widespread rainfall
amounts around and in excess of half an inch over the past day. For
its part, HREF ensemble mean rainfall totals show a widespread 0.5-
0.75in across the western half of the UP, but higher totals in
excess of an inch are possible with some members even as high as
1.5in.

The cold front continues through the eastern half of the U.P.
Wednesday as a secondary shortwave drops down from Canada and brings
light rain showers and maybe a thunderstorm or two back across the
western half of the U.P. Wednesday afternoon behind the front.

Behind the cold front, expect cooler temperatures to dominate the
rest of the extended forecast period as a synoptic troughing set-up
settles over Canada and rotates multiple shortwaves across our
region throughout the rest of this week and upcoming weekend. This
will bring multiple light rain shower chances across our area for
the rest of the extended period, and maybe a thunderstorm or two
during the afternoon hours when daytime heating becomes maximized.
With cooler and a somewhat drier airmass working in, it is not out
of the question that RH falls into the 30s at times throughout the
extended period...but will note that this isn`t very certain given
hit and miss rain chances, rather a cloudy period, and lackluster
mixing in soundings. Winds may be elevated at times throughout the
period, particularly Thursday and Friday with a tighter pressure
gradient over the area, which could enhance drying at the surface.
This would all point to a concern for fire weather into the extended
period, but mitigating this will be the early-week rainfall.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 831 PM EDT Mon Jun 3 2024

Very tricky forecast with clearing skies aloft over a moist and
stagnant low level air mass that has potential to result in
dense fog and VLIFR cigs/vsby. At this time, the worst
cigs/vsby are expected at SAW where cigs have already lowered to
IFR and southerly upslope flow may allow for continued lowering
despite clearing aloft. However, overall confidence is
generally low. Skies recently cleared at IWD/CMX but there are
low clouds around and a bank of fog on Lake Superior that
appears to be expanding this evening. Radiation fog may also
develop at each terminal overnight tonight, but confidence is
highest at SAW. Am not expecting rainfall for most of this TAF
period though drizzle is possible if fog gets thick enough. A
TEMPO group was put in at CMX/SAW overnight to address these
low-probability, but high- impact scenarios. Regardless,
improvement is expected after sunrise with surface heating help
to dissipate fog, where it develops. There is also a chance for
a thunderstorm late in this period, mainly at IWD. Otherwise,
light southerly winds prevail at SAW/IWD with southeast or
easterly winds at CMX.

&&

.MARINE...
Issued at 404 PM EDT Mon Jun 3 2024

Winds generally out of the SE remain elevated across the eastern
half of the lake, gusting to around 20-25 knots for the most part.
However, especially around the Keweenaw where downsloping comes into
play, higher gusts around and even in excess of 30 knots remain
possible into the early evening hours. Winds fall back below 20
knots overnight while a high pressure ridge briefly builds into
the region. This tranquil period will be short-lived as winds
pick up again later in the day Tuesday ahead of our next
approaching frontal system. SSE winds gust to around 20 knots
across most of the lake Tuesday evening through Tuesday night,
with some higher gusts of 25- 30 knots north of the Keweenaw.
After winds briefly fall back behind the passing cold front
Wednesday morning, we could see southwest to westerly winds pick
up to around 20 knots over the west half of the lake Wednesday
afternoon as a secondary shortwave moves through. As additional
shortwaves rotate through our area the rest of this week through
this weekend, expect winds to increase from the west and
northwest at times; we could see westerly winds gust up to 20 to
30 knots Thursday and again to 20 to 25 knots from the
northwest Friday as shortwave lows impact the Upper Great Lakes.

As for other marine concerns this week, expect lingering patchy fog,
dense at times, across most of the lake tonight through Tuesday in
the wake of our rounds of rain today. This patchy fog looks to
persist until the second, stronger cold front moves through Tuesday
night and Wednesday, when the cooler air behind the front could
allow the moisture to mix out. Thunderstorms return late Tuesday
afternoon as the second cold front moves into the far western lake;
some severe weather could be seen over the far west Tuesday
afternoon and evening near Duluth, although the chance for severe
weather is still rather low (~5%); severe hail and winds are the
primary concerns. The thunderstorm activity continues across Lake
Superior from west to east Wednesday until leaving into northern
Ontario late in the day.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Dense Fog Advisory until 9 AM EDT /8 AM CDT/ Tuesday for
     LSZ162-240>243-263.

Lake Michigan...
None.

&&

$$

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