285
FXUS63 KMQT 170718
AFDMQT

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

.KEY MESSAGES...

- Showers into the evening hours. A few rumbles of thunder possible.

- A slight ~30% chance for thunderstorms exists across the
  western UP Friday afternoon and evening then over the
  Keweenaw Friday night.

- A southerly breeze and very warm temps in the 70s and 80s
  Saturday ahead of a cold front that brings a higher ~50%
  chance for afternoon thunderstorms. The strongest storms may
  contain small hail.

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

&&

.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 /FRIDAY THROUGH THURSDAY/...
Issued at 524 PM EDT Thu May 16 2024

Several low to medium-impact forecast challenges persist with the
current forecast package 1) Friday/Saturday afternoon thunderstorm
chances, 2) fire wx concerns interspersed between brief rain
chances, and 3) widespread rain potential next week. Both chances
for thunderstorms include low probabilities for strong storms
capable of gusty winds and small hail, but instability seems
insufficient for severe hazards. Borderline fire wx concerns return
Friday afternoon with elevated conditions possible this weekend,
especially on Saturday when gusty south winds may accompany hot
temperatures >80F. Details of the early next week pattern remain
murky, but potential for frequent rain chances if not widespread
soaking rain seems to be increasing.

Beginning with Friday, the UP will be positioned between systems,
but a weak and low-amplitude shortwave ripples along the northern
periphery of 500 mb ridging during the afternoon hours. This impulse
may be associated with a warm front lifting northeast across the
region. As a result, warm air advection and veering wind profiles
are apparent and would be favorable for thunderstorms -perhaps even
strong storms- if sufficient moisture/instability materializes. HREF
means advertise around 500 J/kg which is insufficient for strong
storms. However, individual CAMs advertise localized pockets of 1000-
1500 J/kg across the interior west, which is sufficient for small
hail and gusty winds. Regardless, the spatial and temporal extents
of this threat appear small and it`s more likely that thunder
doesn`t occur. As the warm front lifts north across the area a
nocturnal thunderstorm threat may emerge on the nose of a ~40 kt
LLJ. Most guidance keeps this activity over the lake, but it could
scrape the Keweenaw so I left schc PoPs. Also with WAA spreading
across the area and EFI guidance highlighting unseasonably warm lows
across the west, decided to nudge the forecast upwards so that
western downslope locations only cool into the upper 50s Friday
night with mid 40s to around 50 elsewhere.

By Saturday morning, 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 supports high temps
surging into the 80s and a stout south breeze should prevent a lake
breeze off Superior, in fact a few downslope locations (e.g. Big
Bay, L`Anse, Ontonagon) may reach the mid-80s. However, south flow
off Lake MI keeps the eastern UP mainly in the 70s to perhaps even
60s along the shorelines. EFI highlights the unseasonably warm temps
well and also hints at the possibility of unseasonably strong wind
gusts across the far west where model soundings indicate potential
for gusts into the 30-35 mph range. 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 also result in afternoon/evening thunder
chances as the systems cold front presses across the area as CAPE
values increase to around 750-1250 J/kg. Bulk shear values are in
the 25-35kt range on most guidance indicating a convective
environment that is barely favorable for marginally severe hail or
winds, but the SPC decided not to outlook our area. Ultimately,
timing of the frontal boundary will be critical for thunderstorm
potential in our area.

A much drier air mass and associated surface ridging follows the
frontal passage for Saturday night into Sunday. Abundant sunshine
and light winds results in deep mixing into an extremely dry mid-
level layer on Sunday. For example, the 12z NAM advertised a -48C
dew point at 734 mb at 1 PM Sunday. Fortunately surface dew points
won`t mix that low, but I still made substantial cuts to Td values
resulting in minRHs around 20% across the interior west. Light winds
less than 10 mph are the silver lining for 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.

Quickly glancing at the long-term period, model support appears to
be increasing for a wet stretch of weather including widespread
soaking rainfall early next week. The latest EPS surface low tracks
develop a low near Rapid City, SD that lifts northeast across MN
into far northwestern Ontario Sunday night into Monday. Warm/moist
air advection ahead of this system brings rain chances back into the
area. As the Ontario low departs on Monday it appears to leave a
trailing frontal boundary across the Upper Great Lakes as a sub-1000
mb surface low develops over the south-central Plains. This
deepening low pressure tracks along the frontal boundary into the
Great Lakes region on Tuesday/Wednesday bringing the potential for
heavy precipitation.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 122 AM EDT Fri May 17 2024

VFR conditions will continue at IWD through the period. LIFR
conditions at CMX will continue until later tonight when MVFR moves
in and then VFR by Fri morning. SAW will have LIFR conditions
overnight and then VFR conditions Fri morning.

&&

.MARINE...
Issued at 524 PM EDT Thu May 16 2024

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 a cold front. Patchy dense
fog is possible in areas of rainfall this evening through tonight. A
few rumbles of thunder are possible this evening across the eastern
lake. Additional thunderstorm chances occur as a warm front lifts
across the lake Friday evening followed by a cold front Saturday
evening. The strongest storms along Saturday`s cold front may
contain small hail, gusty and erratic winds, and frequent lightning.
Thunder chances return Monday as a series of disturbances track
northeast across the Upper Great Lakes region.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...LC
LONG TERM...EK
AVIATION...07
MARINE...EK