519
FXUS63 KMQT 121939
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
339 PM EDT Wed Jun 12 2024

.KEY MESSAGES...

- Showers and thunderstorms expected (80% chance) between 9 pm and 3
am EDT tonight from west to east.

- There is a slight risk (category 2/5) of severe weather for the
western UP, with the main threats being large hail in excess of an
inch and damaging winds in excess of 60 mph. There is a marginal
risk (category 1/5) elsewhere, except for the far east.

- Gusty winds expected Thursday along with lingering showers and
thunderstorms.

- Dry Friday and early Saturday before the return of showers and
thunderstorms later in the weekend.

- Warmer than normal temperatures frequent the forecast, with some
areas approaching 90 for highs by next week.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 244 PM EDT Wed Jun 12 2024

Early afternoon water vapor shows a couple of low-amplitude
shortwaves embedded in fast midlevel flow over the north-central
CONUS. The first is generating lift and a couple areas of showers
along the WI/MI border and western Lake Superior, while an MCS is
ongoing further south into the better instability over southern MN.
No lightning strikes have been noted directly upstream as of yet,
and with HRRR trending a bit drier/less convective for this
afternoon, convection seems to be low probability and thus potential
for thunder was capped at slight chance (<25%) for the remainder of
the afternoon.

Of greater concern is the late evening/overnight period tonight.
Convection is expected to develop rapidly over northern MN this
afternoon as steep (> 8C/km) lapse rates overspread the area. A
classic loaded gun sounding in this area should yield intense storms
assuming that forcing from the second aforementioned low-amplitude
wave and attendant low-level boundary is sufficient, which it should
be. The question for our area is to what extent these storms will
hold together as they cross Lake Superior. The steep midlevel lapse
rates should maintain MUCAPE of 1000-1500 J/kg across the western UP
as the storms arrive. Wind shear is quite impressive both in the low
levels, with a low-level jet of 30-40 kt overspreading the area, and
in terms of deep-layer bulk shear which will max out between 40-60
kt. CAMs vary in their depiction of the incoming convection, but the
HRRR has been relatively consistent in maintaining a broken line of
organized strong/severe storms across the lake. Large hail in excess
of an inch is a threat given the strong shear and steep midlevel
lapse rates, and damaging winds in excess of 60 mph are also a
threat despite the nocturnal period given the strong low-level wind
field and likely maintenance of a respectable low-level mixed layer
as well. SPC slight risk (level 2/5) in effect over the western
counties. Storms should weaken with eastward extent as they outrun
the better midlevel lapse rates and instability, but at least
isolated strong/severe storm threat exists across most of the UP as
SPC Marginal Risk (level 1/5) covers all areas except the eastern
quarter or so. Main timeframe for storms looks to be roughly 01-06Z
from west to east (9 pm-2 am EDT).

&&

.LONG TERM /THURSDAY THROUGH WEDNESDAY/...
Issued at 335 PM EDT Wed Jun 12 2024

The active weather pattern across the CONUS continues through the
long-term forecast. The main features of note at 500mb are a trough
passing over Lake Superior Thursday and a deep cutoff low off the
coast of the Baja California, which will be the cause of active
weather over the weekend. Despite high pressure keeping a day of ,
the overall weather pattern through the long term is wetter than
normal and warmer than normal, with some of the hottest temperatures
of the year thus far forecast for Monday.

Thursday, the aforementioned trough will pass over the area. 850mb
cold advection and dry air behind the trough will allow for 20-30kt
winds to mix down to the surface. EFI shift of tails has backed off
somewhat but the Euro ensemble still calls for the potential of
gusts up to 35 mph. These gusts will almost certainly (90+%) not be
consistently high enough for an advisory but it will still be a
gusty day. CAMs call for some diurnal showers supported by post-
tropa clearing allowing for some radiational heating, but only
isolated thunderstorms are expected. Highs look to be in the 70s for
the most part except for the southern reaches of the UP reaching
into the 80s and some of the near-Lake Superior communities only
seeing highs in the 60s.

Once showers move out of the UP entirely Thursday evening, dry
weather will be over the UP through at least Saturday morning as
ridging aloft builds in and supports a near-1020mb high pressure
over the Upper Great Lakes. Friday will be a slightly cooler day
with highs only in the 60s to low 70s, but highs recover to the mid
70s for Saturday. RHs look to fall into the 40s and 30s, but with
very light winds, weather should be benign to end the work week and
begin the weekend.

Meanwhile, the deep cutoff low over the Pacific will deamplify and
shift northeast through the Rockies. The GEFS shows a low pressure
will develop in the Canadian Prairie, with the GEFS suggesting a
central pressure potentially below 990mb and perhaps into the 970s
mb over Manitoba by Sunday afternoon. With high pressure shifting to
the east, predominantly southerly low level flow will allow Gulf
moisture to surge north, as shown in the NAEFS vapor transport being
at the 90th percentile of climatology along with PWATs of near 1.5
inches. As the weakening trough approaches the Upper Great Lakes and
the cold front of the Canadian Low approaches, multiple lifting
mechanisms for showers and thunderstorms will be present, with PoPs
spreading west to east beginning Saturday PM. As the pattern is
complex, details on the strength and timing of storms is tough to
narrow down, so look for future forecast packages to gain clarity
there, but with the available moisture to work with, ensembles do
show about a 15% chance of daily precip totals to exceed an inch by
Sunday. This is a little lower than the last 24 hours of guidance,
but still enough to maintain some concern about weekend outdoor
plans that would be ruined by a downpour.

The gradual warmup continues into next week, with high 80s in the
forecast for Monday, with widespread low to mid 90s in the 75th
percentile of the NBM. PoPs remain in the rest of the long term
forecast as ensembles show a continued chaotic pattern through mid-
June. The general pattern looks to support ridging over the eastern
CONUS with a persistent surface high off the East Coast, which
should help create southerly to southwesterly flow to advect further
Gulf moisture north. As a result, the CPC outlooks the 8-14 day
period as being more likely to be warmer than normal and wetter than
normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 144 PM EDT Wed Jun 12 2024

Main aviation concerns include timing and strength of potential
thunderstorms, potential for low clouds following the storms at CMX,
and low-level wind shear potential. There are two potential windows
for thunderstorms. The first is roughly 18-22Z at CMX and 20-24Z at
SAW. So far, no upstream convection is noted, and although modest
destabilization is occurring, potential for the first round is too
low to warrant inclusion in the TAFs. The second and more likely
round is roughly 01-04Z at CMX/IWD and 03-05Z at SAW. Storms in this
timeframe could produce strong wind gusts in excess of 40 kt as well
as large hail to around an inch at CMX/IWD. Storms will be weakening
with eastward extent but brief gusty winds and small hail still
could occur at SAW. Vsby could fall to IFR/MVFR in any storms. After
the storms, cloud bases will likely lower to MVFR/IFR late tonight
at CMX before rising/scattering by around 12Z Thu. Low-level wind
shear will be a concern at all sites tonight as a strong
southwesterly low level jet moves overhead. Outside of storms and
the period of possible low clouds at CMX, VFR conditions are
expected.

&&

.MARINE...
Issued at 335 PM EDT Wed Jun 12 2024

This evening, strong to severe storms are expected to be over the
western half of the lake as storms come off of the MN Arrowhead and
reach the western UP. Otherwise, southerly winds will broadly remain
below 20 kt. Behind a cold front driving through Thursday, cold
advection will drive gusty winds aloft to the surface, with westerly
to northwesterly wind gusts of around 25 knots expected on Thursday.
High pressure building over the Upper Great Lakes into the weekend
will keep wind gusts below 20 kt Friday through Sunday morning, when
a cold front will bring a return of thunderstorm chances. Waves will
largely be below 4 ft until Sunday when waves along the US/Canada
border on Lake Superior will grow to 4-5 ft.

&&

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

&&

$$

SHORT TERM...Thompson
LONG TERM...GS
AVIATION...Thompson
MARINE...GS