261
FXUS63 KMQT 171113
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
713 AM EDT Fri May 17 2024

.KEY MESSAGES...

- There is a slight (30%) chance of thunderstorms across the western
UP this afternoon and evening over the western UP, lingering across
the Keweenaw into tonight.

-Breezy south winds and very warm temps in the 70s and 80s Saturday
ahead of a cold front that will bring scattered afternoon/evening
thunderstorms. The strongest storms may contain small hail.

-Elevated fire weather possible on Saturday then very dry with
light winds on Sunday.

-More rain chances early to middle of next week as a series of
disturbances moves across the area in a developing warm and moist
southerly flow.

&&

.UPDATE...
Issued at 711 AM EDT Fri May 17 2024

With light winds and plenty of lower level moisture in the wake
of the exiting shortwave, widespread fog - some of it rather
dense - developed over the eastern half of the UP early this
morning. Fog quickly mixes out over the next couple of hours,
then we will just be left with patchy high cirrus and plenty of
sunshine. Temperatures were able to drop a few degrees lower
than forecast in some pockets throughout the western UP, with
some spots even dipping into the upper 30s! Temperatures will
quickly recover today, with most of the area peaking well into
the 70s.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 318 AM EDT Fri May 17 2024

Showers have come to an end in the wake of an exiting shortwave that
is currently swinging into Ontario. Drier midlevel air is apparent on
water vapor over the area, and skies are clearing out across the
western half of the UP. Satellite shows plenty of lingering low
cloud cover across the eastern UP, as well as the Keweenaw and Lake
Superior, and even where skies have cleared, patchy fog is apparent
in surface observations and webcams. Temperatures are dropping into
the lower 40s already where skies have been able to clear, but
remain in the upper 40s and lower 50s where low clouds linger.
Temperatures shouldn`t fall back much further tonight.

Patchy fog mixes out into the daytime hours, though at least some
patchy marine fog may linger into the  morning. Expect otherwise
sunny skies to start the day with weak ridging over the area as the
Great Lakes look to be situated in between two systems. However,
rain chances sneak into the western UP into the late afternoon with
a subtle shortwave grazes the area, coincident with a warm front
lifting into the Upper Midwest. Given weak forcing, would not expect
much out of this, with HREF guidance showing a few hundred j/kg of
CAPE. That said, various individual models continue to show patches
of 500-1000j/kg of CAPE during the afternoon, indicating a potential
for some stronger cells with small hail or a good wind gust. Still,
coverage of any showers looks spotty at best with a rather weak
trigger for anything to develop at all. Otherwise, expect warmer
temperatures ranging well into the 70s across most of the interior
UP, while lake breeze development keeps areas closer to the
lakeshores in the 60s to lower 70s.

Tonight, though the warm front should be lifting north over
Superior, the potential for some convection lingers at least the
first half of the night over the western UP as a 40kt LLJ becomes
directed into the area. Will note, however, that guidance continues
to favor this staying mainly over the water. Otherwise, expect
partly cloudy skies, and maybe some patchy fog where any showers
would have developed during the afternoon. Temperatures stay quite
mild, bottoming out in the mid and upper 40s across the eastern UP
while the western half of the UP falls only as far as the 50s. Some
of the typically warmer, southerly downsloping areas may even stay in
the upper 50s overnight.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 320 AM EDT Fri May 17 2024

Highlights of the extended forecast include very warm conditions
this weekend with the potential for elevated fire weather conditions
at times, then more opportunities for possible widespread rain next
week.

Beginning Saturday, the UP will be squarely in the warm sector of a
surface low near Lake Winnipeg with 850 mb temps of 14-16C spreading
across the UP. This unseasonably warm air mass will support high
temps most locations in the lower to mid 80s with the highest
readings most likely for downsloping areas along Lake Superior west
and central where breezy south winds in the tightening gradient
ahead of the approaching frontal boundary could gust as high as 30-
35 mph at times per model soundings. However, south flow off Lake MI
will keep the eastern UP mostly in the 70s to perhaps even 60s
readings along the shorelines. ECMWF EFI highlights the unseasonably
warm temps well, and like the model soundings, also hint at the
possibility of unseasonably strong wind gusts across the far west.
The combination of hot temps and gusty winds suggests potential for
elevated fire wx conditions, but the main limiting factor is RH
values as dew points surge to around 50F.

Elevated dew points could also result in late afternoon/evening
thunder chances as the system`s cold front presses across the
area. SPC has placed the west half of the UP in a marginal risk
of severe storms on Saturday. However, believe there is some
question on the degree of fcst instability across the area. The
NAM soundings depict a drier airmass with limited CAPE
(generally 500 j/kg or less) and more capping at mid-levels
while the GFS shows MLCAPE values increasing near 1000 J/kg
range in the west with almost no capping during the afternoon
based on more aggressive ramp up of sfc dew points rising well
into the 50s. If the more moist and unstable GFS verifies then
bulk shear values forecast in the 30-40kt range could possibly
generate a few stronger storms with marginally severe hail or
gusty winds. Ultimately, the threat of storms or severe
potential will hinge on how much sfc dew points mix out during
the day on Saturday ahead of the front. Gut feeling is that the
drier and more stable NAM soundings may have a better handle on
the fcst instability, leading to perhaps decreased coverage for
t-storms and thus a lower threat of SVR storms.

A much drier air mass and associated surface ridging follows the
frontal passage for Saturday night into Sunday. Abundant sunshine
and light winds will result in deep mixing into extremely dry mid-
levels on Sunday. For example, the 00z NAM fcst sounding advertised
a -33C dew point at 760 mb at 1 PM Sunday. Fortunately, surface dew
points won`t mix that low, but will still incorporate the local
mixed dew point tool to cut back on Td values resulting in min RHs
closer to 20% across the interior portions of the cwa. The good news
is light winds less than 10 mph should ease fire wx concerns,
because critically low RHs appear nearly certain across interior
portions of the UP. Lake breeze activity should limit fire wx
concerns along the shorelines due to cooler temps and higher RHs.
Expect max temps reaching near 80F over much of the interior west
half and mid to upper 70s over the interior east half. Developing
lake breezes will keep readings near the Great Lakes shores in the
mid to upper 60s.

Models advertise a mid-level trough amplifying over the western
CONUS early next week. Periodic shortwaves in a warm/moist sw flow
developing ahead of the western CONUS trough will bring more rounds
of showers into the area early to mid next week. The first shortwave
moves through late Sun night into Monday bringing the initial batch
of showers for early next week. It looks like the best chance for
widespread and possibly heavy rainfall will be in the late Tue into
Wed time frame when models indicate more substantial shortwave
energy lifting across a nearly stationary frontal boundary draped
across the area. Model uncertainty increases later into the week but
it certainly looks possible that some scattered showers could linger
at least into Thursday as temps trend cooler in the wake of the
midweek low pressure system/frontal boundary pushing off to the
east.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 711 AM EDT Fri May 17 2024

With fog and low stratus lifting out this morning, all terminals are
returning to VFR with just some patchy cirrus over the area the rest
of the morning. There is a chance for a few showers and some rumbles
of thunder to move into the western UP later today and into tonight,
which may impact IWD and CMX. However, timing and coverage of
convection is too uncertain to include anything more than vicinity
showers in the TAF at this time. Otherwise, expect light and
variable winds to turn more to the southeast through the TAF period.

&&

.MARINE...
Issued at 320 AM EDT Fri May 17 2024

Stable conditions will lead to light winds of generally 20 knots or
less continue today into early next week, except for Saturday
afternoon and evening when southerly gusts of 20-25 kts are forecast
ahead of an approaching cold front. Patchy dense fog is possible
into early morning from last night`s rainfall. Thunderstorms are
possible this evening over west and north central Lake Superior as a
warm front lifts across the lake. More thunderstorms are possible on
Saturday into Saturday night as the same system`s cold front moves
across the area. These storms may contain small hail, gusty and
erratic winds, and frequent lightning. More thunder chances return
late Sun night into Monday and then again late Tuesday into Tuesday
night as a series of disturbances track northeast across the Upper
Great Lakes region.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Dense Fog Advisory until 2 PM EDT this afternoon for
     LSZ249>251-266-267.

Lake Michigan...
  Dense Fog Advisory until 11 AM EDT this morning for LMZ221.

  Dense Fog Advisory until 5 PM EDT this afternoon for LMZ248-
     250.

&&

$$

UPDATE...
SHORT TERM...LC
LONG TERM...Voss
AVIATION...LC
MARINE...Voss