985
FXUS63 KMQT 220532
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
132 AM EDT Wed May 22 2024

.KEY MESSAGES...

- First round of showers and thunderstorms are already ongoing
  and will lift north over the west half of the UP potentially
  bringing small hail and stronger winds.

- Second round of thunderstorms moves from west to east this
  evening into tonight, bringing mainly some heavy rain showers
  and winds; there is a slight chance for all severe weather
  threats along this line.

- Windy conditions develop behind the system on Wednesday. Wind
  gusts of 50 to 60 mph are possible along the western lakeshore
  and Keweenaw.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 319 PM EDT Tue May 21 2024

This afternoon brings the first wave of showers and possibly some
isolated thunderstorms to the UP with a second and more noteworthy
round expected this evening into tonight. A slight risk from the SPC
over the south-central seems to fit well for the going forecast with
potential for all severe weather threats accompanying the second
line of thunderstorms.

Latest WV imagery and RAP analysis has the first shortwave currently
over MN and northwest WI which is lighting up the radar data over
the western UP. This will continue to expand north and east over the
west half of the UP as the shortwave and mid level warm front lift
north, aided by isentropic ascent. With current RAP analysis showing
SBCAPE around 100 j/kg with mid level lapse rates below 6.5 C/km and
the 5/21 12z HREF mean SBCAPE holding around this through the
afternoon as the boundary lifts north, some isolated thunderstorms
are possible to bring some small hail. Severe weather is expected to
hold off until the second round.

The more vigorous shortwave is currently situated over east NE with
the associated sfc low over west IA. This shortwave trough will take
on an increasingly negative tilt as it lifts north-northeast through
the Upper MS Valley this evening and then across northern MN and
into Ontario later tonight. The associated sfc low will rapidly
deepen today aided by strong upper divergence from a coupled upper
jet structure (right entrance region of a 130 kt jet max over
northern Ontario and the left exit region of a 110 kt jet max over
the Southern/Central Plains). The most recent HREF mean has the low
deepening to around 984 mb near the MN/Canadian international border
by 12Z Wed as the center tracks just west of Lake Superior later
tonight. With this more northwest sfc low trend in the last 24 hours
has increased the severe weather potential. CAMs are in fairly good
agreement on this second round developing a QLCS over the western UP
this evening, quickly tracking east into tonight. With bulk shear
around 45-50kt, MUCAPE up to 1000 j/kg, and mid level lapse rates
around 7C/km, some severe thunderstorms are possible. With strong
LLJ around 60-70 kts, this should contain the severe weather threats
to winds. That said, mid level lapse rates could support hail up to
1 inch and low LCLs around 1kft with some low level helicity does
leave a low chance (~2% chance along WI state line) for a quick
tornado spin up. The limiting factor for severe weather is the
timing of the storms, as we progress into the evening and lose
daytime heating, storms are expected to weaken. Another factor in
limiting severe potential for the eastern UP is onshore flow off
Lake Michigan.

Most locations will see between half an inch to inch of rainfall
from this system with the highest amounts west. Models show shower
coverage diminishing significantly late tonight as we get into the
dry slot behind the front along with q-vector divergence/subsidence
as the system continues to lift north. Lows tonight will stay mild
in the 50s, cooler in the west.

&&

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
Issued at 350 PM EDT Tue May 21 2024

The extended forecast is dominated by two low pressure troughs
during the period, one west of Thunder Bay and north of the
Arrowhead of Minnesota by Wednesday morning, and another over the
Seattle area Wednesday morning making its way across the Upper
Midwest Friday afternoon through Friday night. While the first low
will be northwest of Lake Superior Wednesday, strong winds from
behind the first low will be the main story for the long term,
creating windy conditions across the area  (especially the west
where a High Wind Watch and Wind Advisories were issued).

As an impressively deep 986mb low continues lifting northwest from
just west of Thunder Bay towards James Bay Wednesday, a strong low-
level jet from between 5 and 30 thousand ft will move across Upper
Michigan, allowing for windy conditions to develop over the U.P.,
particularly the west where the strongest winds of the LLJ reside.
While 70 mph is the highest possibility (<10% chance), winds up to
50 to 60 mph are expected across the western U.P. along the
lakeshores and the Keweenaw. This will cause unsecured items to the
lofted away and for driving to become hazardous in spots. Therefore,
a High Wind Watch and a Wind Advisory have been issued for Ontonagon
and Gogebic counties Wednesday. While I`m confident that Ontonagon
will see wind gusts up to 45 mph, I`m only around 60% confident that
Ironwood and northward will see gusts up to that high. Likewise, I`m
only 70% confident that northern Houghton and Keweenaw counties will
see wind gusts up to around 60 mph Wednesday too. The main concern
is how well we will mix the higher winds down to the surface across
the area Wednesday; with low-level stratus looking to hang on until
the afternoon hours, we have have a more difficult time doing so.
Nevertheless, the friction that the land will cause along the
lakeshores (as well as the increase in elevation) will help to
increase the wind speeds too. As we move into Wednesday night, we
will lose the diurnal mixing from the sunlight, and thus more stable
air in the boundary layer will prevent the higher winds aloft from
mixing down. While we will likely (80+% chance) see breezy
conditions continue over the Keweenaw Wednesday night, expect
calmer winds across the rest of the U.P. by midnight.

Besides the winds Wednesday, there is a 20% chance that we will see
some light rain showers moving through the central and east
Wednesday before more light rainfall from moisture that`s wrapped
around the low returns and brings isolated showers and thunderstorms
back over the western half by the afternoon hours. As the low
continues to pull away Wednesday night, some of the CAMs hint at a
line of light rain showers moving over the western half late as a
secondary shortwave rotates around the low over us. However, the
shower activity is expected to die out Thursday morning as weak
ridging begins to build back into the area. With warm air advection
returning to the area Thursday, expect highs in the 60s near the
Great Lakes to the 70s in the interior areas. With mostly sunny
skies being over the area Thursday, we could see some strong
dewpoint depressions develop, possibly getting min RHs down into the
low 30 percents in the interior west. There is a chance that some
convection will pop up during the afternoon hours Thursday as a
localized sfc low moves through the U.P.. Whether this occurs or not
will depend if this sfc low materializes, and if so where it tracks.
As it stands right now, I think the NBM`s 30% handles these rain
chances fairly well.

Our second big low of the period looks to impact us around the
Friday through Friday night time period. While we are looking to be
initially dry Friday, especially over the east where min RHs could
dip into the lower 30 percents, rain showers and thunderstorms from
the approaching low look to move into the west by no later than the
afternoon. I lowered thunderstorm chances from likely to chance
wording over the interior west late Friday afternoon into early
Friday evening as guidance could change rapidly over the next 3 days
in regards to the track of the low (and thus thunder chances). That
being said, should everything come into place and the low track just
right, we could see some severe weather return to the western half
as MUCAPEs could get over 1000 J/kg and 0-6 km bulk shear be around
40 to 50 knots. As the cold front of the low moves over the U.P.
Friday night and Saturday morning, expect the rain chances to cease
behind it.

Dry weather returns for this weekend as ridging builds across our
area. For the beginning of next week, model guidance begins to
significantly diverge; we could see dry conditions and ridging
continue, or we could see a Colorado low lift through the Plains
into the Great Lakes and bring more rainfall to the area.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 132 AM EDT Wed May 22 2024

With TS now beyond all three TAF sites, -SHRA continues into the
early morning hours, ending around 12Z. Throughout the late morning,
ceiling heights will gradually improve, with all sites expecting VFR
conditions by 18Z. Gusty SW winds are expected today, with the
highest gusts up to 45 kt at CMX around 20Z, with gusts around 30 kt
this afternoon at IWD and around 25 kt at SAW. A second round of -
SHRA is possible at all 3 TAF sites in the late afternoon/early
evening, but chances of precip are only around 30 percent, so SHRA
is left out of the TAF at this time, but VCSH may be added in for
later issuances. Precip and wind gusts fall off in the late portions
of the TAF, though some LLWS may be present at SAW and CMX, but
confidence is too low to include in the TAFs at this time.

&&

.MARINE...
Issued at 412 PM EDT Tue May 21 2024

East-northeasterly winds are increasing to gales of 35 to 40 knots
this afternoon into this evening over the far western lake as an
impressively strong low pressure lifts from Iowa into northern
Ontario tonight. As this occurs, expect winds to pick up over the
central and eastern portions of the lake to east to southeasterly
gales of 35 to 40 knots as winds in the far west slacken. However
the winds pick up over the western half of the lake again Wednesday
as a low-level jet moves over. Southwest to westerly gales of around
40 knots are expected over the west half Wednesday, with a few high-
end gales to 45 knots possible near Isle Royale and a few storm-
force gusts up to 50 knots possible near the Keweenaw. As we move
into Wednesday night, more stable conditions develop in the
atmosphere, dropping the winds over Lake Superior to below gales by
midnight. The winds continue to diminish into Thursday afternoon,
when light winds of 20 knots or less return to the area. The light
winds continue until Friday, when another low pressure lifting from
the Northern Plains towards Lake Winnipeg brings northeasterly winds
of 20 to 30 knots back across the western half of the lake. West to
southwesterly winds of 20 to 25 knots could be seen over the western
half from late Friday night through Saturday behind the passage of
the low and its cold front. Behind this, expect light winds of 20
knots or less across Lake Superior for the rest of this weekend as
high pressure ridging moves over the area.

As for thunder chances over Lake Superior for the next several days,
thunder chances continue to develop from the far western lake this
afternoon throughout the rest of the lake tonight before ending
Wednesday. While it`s not expected, we could see some severe hail
and winds with these thunderstorms. Therefore, mariners should watch
the radar and keep up with the latest forecasts in order to avoid
the possibility of hitting those conditions. We could see
thunderstorms return near the southern lakeshore Thursday afternoon
as a weak sfc low moves looks to move through Upper MI. The
thunderstorm chances again return Friday as the second low pressure
system moves north with time. The thunder chances with this low
continue until Saturday morning, when the cold front finally pushes
through the eastern lake.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  High Wind Watch from 6 AM EDT this morning through this
     evening for MIZ001-003.

  Wind Advisory from 9 AM EDT /8 AM CDT/ this morning to 10 PM
     EDT /9 PM CDT/ this evening for MIZ002-009.

Lake Superior...
  Gale Warning until 8 PM EDT /7 PM CDT/ this evening for LSZ162.

  Gale Warning from 7 AM EDT /6 AM CDT/ this morning to 8 PM EDT
     /7 PM CDT/ this evening for LSZ240-241.

  Gale Warning until 11 PM EDT this evening for LSZ242>244-263-
     264.

  Gale Warning until 11 AM EDT this morning for LSZ245>251-
     265>267.

Lake Michigan...
None.

&&

$$

SHORT TERM...Jablonski
LONG TERM...TAP
AVIATION...GS
MARINE...TAP