519
FXUS63 KMQT 221733
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
133 PM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Today`s rain will continue for central and eastern Upper
  Michigan, before a lull moves in this evening. Another wave
  of rain expected to move into the west this evening, then
  progress into the eastern U.P. tonight.

- Additional rainfall amounts of half to one inch possible this afternoon
  in the east. Tonight up to half inch of additional rain
  possible west and a quarter inch east.

- A few thunderstorms possible (~40%) Sunday in the west half,
  no severe weather is expected.

- Patchy fog possible (~30%) Monday morning, especially if
  preceded by rain showers.

- Dry during the day Monday, but ~15% chance of strong to
  severe thunderstorms overnight in the west.

- Warm and muggy Tuesday, 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 131 PM EDT Sat Jun 22 2024

Current GOES 16 Water Vapor and IR imagery, coupled with current
radar data, show this morning`s precip shield spread across the
central and eastern Upper Michigan. Across western Upper Michigan,
radar returns are becoming spotty with some breakage in the cloud
cover noted in northern WI south of the Apostles. In the east, rain
showers, with some embedded moderate to heavy rain showers are
currently being observed. MRMS estimates for rainfall, so far, in
this event are estimated ~0.25 inches or less far west and Keweenaw,
widespread 0.5 to 2 inches central, and up to ~0.5 inches in the
east. As we progress through the remainder of the afternoon, expect
another 0.5 to 1 inch of rain in the east while the western lull
spreads into the interior west/central. A canopy of overcast skies
have blanketed the region today, which has limited daytime heating.
So far, highs have only climbed into the mid-upper 50s to low 60s
across the region.

Current mesoanalysis places a warm front over southern Wisconsin
eastward into lower Michigan, with a surface low over central
Wisconsin and a second low trailing over Iowa. Over western
Minnesota, a shortwave pressing eastward will force both eastward,
enabling the central Wisconsin low to deepen and press east across
Lake Michigan and to near the Straits/Lake Huron by Sunday 12z while
the Iowa low drags across southern WI along the frontal boundary.
Additional forcing between these 3 features will support another
wave of rain into the west this evening, which spreads east along
the low`s northern flank as the low transits the Great Lakes. CAMS
are a little mixed on shower coverage in this wave, but appear to
consistently suggest lighter rain then we received through the day
today so far. Recent HREF and NBM runs validates this with
probabilities of >0.5 inches at 60% or less. General consensus among
the packages suggest an additional 0.5 inches would be most likely
across the west while the east half sees up to another 0.25 inches
tonight. Expect patchy fog to develop overnight as we cool into the
low 50s to upper 40s west and mid-upper 50s east.

&&

.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 /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 132 PM EDT Sat Jun 22 2024

Rain and low ceilings will continue this afternoon across Upper
Michigan, impacting primarily KIWD and KSAW with IFR and LIFR
ceilings. KCMX is north of the main precip shield and should remain
VFR into this evening.

After rain ends west to east this afternoon, another wave of
showers, potentially mixed with thunderstorms will move into western
Upper Michigan. This will impact KIWD/KSAW and maybe KCMX with
continued low ceilings. KCMX may dip into MVFR at this point. Expect
KSAW/KIWD to remain LIFR or IFR for a majority of the night due to
low ceilings and fog/mist.

&&

.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...JTP
LONG TERM...GS
AVIATION...JTP
MARINE...GS