102
FXUS63 KMQT 220900
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
500 AM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Wet pattern continues into early Sunday with some periods of
  patchy fog.
- The heaviest rainfall should stay south of the UP, but there
  is still a slight chance (15% chance) for locally heavy rain
  resulting in minor flooding impacts across south central and
  southeast portions of Upper Michigan.
- A few thunderstorms possible (~40%) Sunday in the west half,
  nothing severe.
- Dry during the day Monday, but ~15% chance of strong to
  severe thunderstorms overnight into Tuesday in the west.
- Warm and muggy Tuesday afternoon, highs in the low- to mid-
  80s, dew points in the 60s
- Dry Wednesday into Thursday, but pattern going forward
  remains generally warm and wet.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 444 AM EDT Sat Jun 22 2024

     More showers to move in today and tonight with the
heaviest/steadiest rainfall central and east...

Latest water vapor imagery and current RAP analysis currently show
broad mid-level ridging over the Upper Great Lakes early this
morning but this will give way to a couple of upstream shortwave
troughs of interest, one over southern/central MN and another over
western SD. The initial shortwave trough over MN is expected to move
across the Upper Great Lakes today with the second trough from the
Dakotas expected to move across the area tonight. Both these
shortwaves along with an associated sfc low pressure system will
support periods of rainfall across the U.P. today into tonight.
Based upon the tracks of the shortwaves and the associated sfc low
along with the most favorable fcst forcing from mid-level fgen and
isentropic ascent would expect the heaviest and most prolonged
rainfall to occur over south central and east half portions of the
U.P. today through tonight. Weak elevated instability could support
isolated t-storms as well, mainly south central and southeast.
Currently, only isolated to scattered light rain showers are
occurring over south central UP but expect this coverage to increase
to numerous or widespread toward sunrise as it spreads slightly
farther north and east in response to the shortwave trough moving in
from MN. It is worth noting that WPC does have the southeast half of
the U.P. (roughly along and east of a line from Iron Mountain to
Harvey) in a slight risk for excessive rainfall today into tonight
as PWATs range from 1.5 to 2 inches across much of the area or
nearly 200% of normal. Would expect the most vulnerable areas for
risk of flash flooding would be urban or poor drainage areas
southeast if training of stronger showers/storms occurs over these
areas. With the expected moist conditions will also continue to
carry a mention of patchy fog in the grids through much of the
period.

Under mostly cloudy skies, temps today will generally be in the
lower to mid 60s, although could be in the upper 50s along the Lake
Superior shore. Lows tonight will be mostly in the 50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 458 AM EDT Sat Jun 22 2024

Sunday into next week, persistent 500mb ridging over the southwest
to south-central US with longwave troughing over the eastern coasts
of North America leaves the Upper Great Lakes in the main path of
shortwaves riding above the ridge and into the larger trough. The
resulting surface features will result in at least three distinct
rounds of rainfall in this period with brief dry periods between
them. The best chances (~15%) for strong thunderstorms will be with
the precipitation Monday night into Tuesday. Without long-duration
southerly flow, temperatures generally remain near-seasonal, with
the exception of Tuesday when temperatures look to climb to around
80 with dew points in the 60s.

Beginning Sunday, the prior round of precipitation from earlier in
the weekend will be exiting to the east. However, a backdoor
shortwave following behind the main feature may kick off a second
round of showers tracking from northwest to southeast during the day
on Sunday, primarily for the west. CAMs differ somewhat on the
coverage of these showers, with the WRFs generally showing scattered
coverage, the NAM Nest with isolated to no showers, and the 00Z HRRR
showing a much wider band of thunderstorms. Blending those solutions
arrives mainly around the WRF solutions, with a band of ~40% PoPs
over the western to central UP during the daytime Sunday. While the
HREF maximum suggests up to 1k J/kg of SBCAPE is possible, the
ensemble mean is a lot closer to 500 J/kg, which puts these showers
within the "a few thunderstorms, but nothing severe" regime. While a
brief heavy downpour is possible within these showers, the
probability of flooding rainfall is on the order of less than 10%.

Following the passage of these showers will be some shortwave
ridging that will support a weak ~1015mb high pressure over the UP
overnight Sunday into Monday. Depending on how much moisture was
deposited in the near-surface layer with prior showers, some patchy
fog is possible Monday morning, with ENS meteograms showing around
30% of members with reduced visibility for the interior west. It is
worth noting that nearly every ENS ensemble member that shows fog,
the fog is dense, so it will be worth watching the hi-res guidance
in the next 12-24 hrs to see if further model support for dense fog
grows. Otherwise, Monday looks to be a mainly quiet day, with a
possible lake breeze shown in the NAM wind grids but otherwise not
much notable weather during the daytime.

Meanwhile upstream, a low pressure will deepen to near 990mb over
central Saskatchewan and Manitoba. This will allow for moisture-rich
southerly flow to set up late Monday, with both GEFS and Euro
ensemble CAPE probabilities of over 1k J/kg over 50% for much of the
interior western and central UP by Monday night and 20-30% chance of
2k J/kg. The mainly southerly surface flow contrasted with the
mainly westerly flow aloft will create a supportive shear profile
for the maintenance of storms, but as the low pressure will be well
to the north of the Great Lakes, uncertainty in forcing is high at
this time. Timing-wise, the most likely chance for strong
thunderstorms will be during the overnight period, so attention will
need to be paid towards whatever storms fire in the evening further
upstream to determine what happens overnight in the UP. Despite the
uncertainty in forcing and inopportune timing, the ingredients
present are enough for a SPC Slight Risk for late Monday night over
the west.

Southerly winds at the surface persist into the daytime hours
Tuesday, which the warm advection combined with radiational heating
will allow Tuesday to be the warmest day of the week, with the most
likely high temperatures for Tuesday being in the low to mid 80s,
though the 75th percentile shows some isolated spots of 90s. It
could also be a muggy day as forecast dew points approach 70.
Eventually, winds will veer westerly behind the front draped from
the long-away low pressure and temperatures will moderate somewhat.
A few diurnal thunderstorms are possible, especially if the lifting
from the front is on the stronger end of guidance, but PoPs are
generally expected to be around 30% Tuesday afternoon to evening.

While uncertainty does begin to grow around the Wednesday timeframe,
the majority of model guidance shows the most prolonged period of
dry weather setting up as a high pressure transits the Great Lakes
basin Wednesday and Thursday. This sets up another northern Rockies
low pressure forming by Thursday, which will most likely eject
towards and north of the Great Lakes by Friday and the weekend,
though the range of possibilities grows significantly regarding
timing, location, and intensity of showers, so the details will have
to wait. Overall, nothing in the ensembles shows any major shift in
the pattern, which lines up with the CPC continuing to outlook the
UP with best chances for above average temperature and precipitation
even into the first portions of July.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 140 AM EDT Sat Jun 22 2024

Next round of showers will move in overnight and will bring
deteriorating conditions with them. IWD will be VFR overnight
and then IFR Saturday with LLWS coming in late Sat afternoon
into the evening. CMX will be VFR and then by late Saturday
afternoon, rain moves in there with LLWS and MVFR conditions
setting in by evening. SAW will be VFR until around 12Z Saturday
morning when rain moves in and then drops to MVFR. By late Sat
afternoon, heavier rain and IFR/LIFR conditions move in. LLWS
sets up at SAW by Sat evening.

&&

.MARINE...
Issued at 458 AM EDT Sat Jun 22 2024

A deepening low pressure system will gradually lift into the region
today before exiting into Ontario Sunday morning. As this transit
occurs, expect northeasterly/easterly winds across Lake Superior
before becoming northerly tonight and northwesterly by Sunday
morning. Light winds of 20kts or lower are mostly expected in this
event, although northeast winds going down into the Duluth Harbor
Saturday may climb to near 25 kts at times. Additionally, as winds
shift to the north Saturday night, expecting an increasing to near
20 knots across central and eastern Lake Superior as the peak
pressure gradient force shifts through. Winds lighten to 20kts or
less Sunday and predominately remain there until at least Tuesday.
At this point, expecting southwesterly winds to increase to near 25
kts ahead of a transiting cold front.

Thunderstorms will be possible, mainly Sunday afternoon/evening and
then again Monday night into Tuesday. Waves will be strongest in the
vicinity of Duluth Harbor this afternoon (around 4 feet) and between
Isle Royale and the Keweenaw Peninsula Tuesday night (4-6 feet).

&&

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

&&

$$

SHORT TERM...Voss
LONG TERM...GS
AVIATION...07
MARINE...GS