703
FXUS63 KMQT 181113
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
713 AM EDT Sat May 18 2024

.KEY MESSAGES...

-Breezy south winds and very warm temps in the 70s and 80s today
 ahead of a cold front that will bring scattered
 afternoon/evening thunderstorms. The strongest storms may
 contain small hail.

-Borderline elevated fire weather expected this weekend with breezy
 conditions today then very dry with light winds on Sunday.

-More rain chances early to middle of next week as a series of
 disturbances moves across the area in a developing warm and
 moist southerly flow.

&&

.UPDATE...
Issued at 713 AM EDT Sat May 18 2024

The forecast remains on track this morning, with a few showers and
rumbles of thunder re-developing across far western Lake Superior.
These may graze our western shores through the morning. Otherwise,
temperatures this morning hover in the 40s and 50s across most of
the morning, though some spots in the western UP managed to stay
above the 60 degree mark this morning.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 335 AM EDT Sat May 18 2024

Morning RAP analysis shows midlevel troughing digging into the
Northern Plains, extending out from deep low pressure centered over
Lake Winnipeg. An embedded vort max and co-located surface low are
apparent over the Dakotas. Water vapor imagery reveals drier
midlevel air immediately behind this. Warm, more moist air continues
to be pumped into the Upper Midwest as we remain comfortably in the
warm sector, with with robust SSW flow courtesy of a 40-50kt LLJ
directed into the region. A few rain showers linger across the
western UP and over Lake Superior with an initial weak shortwave
moving through. However, another round of convection is expected to
move over western Lake Superior and possibly scrape the western UP
as the exit region of the jet slides eastward. A few rumbles of
thunder will be possible. Otherwise, skies remain mostly clear
across the eastern half of the UP, but cloud cover is apparent to
the west and across Superior with this spotty convection.
Temperatures across the eastern UP are falling into the 40s and
lower 50s, but to the west, with more cloud cover and southerly
downsloping winds, temperatures are coming in much warmer with lows
expected to range in the mid and even upper 50s.

As we head into the daytime hours, morning convection largely stays
offshore with a sunny start expected for most of the UP. 850mb
temperatures climbing up to 14-16C will yield highs well into the
70s to lower 80s across much of the area. The Lake Michigan
shoreline will be cooler with southerly onshore flow; temperatures
there may struggle to get out of the 60s. The tightening pressure
gradient ahead of the Plains system, along with deepening mixing
during the daytime hours, will produce gusty southerly winds with
most of the area gusting up to 20-25mph during the afternoon. Where
southerly flow is downsloping, particularly across Gogebic and
Ontonagon counties, higher gusts around and in excess of 30mph are
possible (hi-res ensemble guidance up to 70% chance for such gusts).
Windy conditions in combination with hot temperatures will lead to
borderline elevated wildfire potential. The area of uncertainty
remains the depth of mixing, with the hi-res guidance favoring
deeper mixing compared to the global models. As of right now,
continued to favor pockets of RH dropping to near 30%, but if the
deeper mixing can play out, even lower values will be possible.

Meanwhile, the shortwave over the Dakotas will swing into MN by the
afternoon and eventually into northern Ontario this evening. An
associated cold front quickly moves through the UP this evening,
touching off another round of convection. Simulated reflectivity
continues to favor a narrow line of showers/storms reaching our
western shores around 21Z, reaching M-95 by 02-03Z and quickly
moving eastward out of the UP between 06-08Z. MLCAPE will be up to
500-1500j/kg just ahead of the front, with around 30-40kts of bulk
shear indicating the potential for some strong to marginally severe
storms. The main threats with this setup would be hail and gusty
winds. The area of greatest concern would be the western half of the
UP; by the time the front reaches even the central UP, we`ll have
run out of daylight and will be stabilizing. As far as rain totals
ensemble guidance favors a quick 0.10-0.20in of rain for the most
part, but there is a chance (30-40%) for heavier amounts up to a
half inch in any heavier downpours.

Skies quickly clear from west to east behind the front while winds
shifting over to the west turn calm. Expect lows ranging in the
upper 40s to lower 50s across most of the area.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 325 AM EDT Sat May 18 2024

After a continued warm and very dry day on Sunday, the focus then
shifts to a couple of widespread rain events for early/mid next week
before a transition to a period of below normal temperatures by late
week.

Beginning Sunday, surface ridging and its associated much drier air
mass will take hold in the wake of tonight`s frontal passage.
Abundant sunshine and light winds will result in deep mixing into
extremely dry mid-levels during the day. For example, the 18z NAM
fcst soundings valid at 18z Sunday over several of the interior west
half sites show -30C or drier dew points at nearly 800 mb or
approximately 5 kft AGL. Fortunately, surface dew points won`t mix
that low, but by incorporating the local mixed dew point tool I did
cut back on Td values resulting in min RHs closer to 20% across the
interior portions of the cwa. The good news is light winds generally
10 mph or less should ease fire wx concerns. Lake breeze
activity should limit fire wx concerns along the shorelines due
to cooler temps in the 60s and higher RHs. Expect max temps
reaching near 80F over much of the interior west half and mid to
upper 70s over the interior east half.

Models advertise a mid-level trough amplifying over the western
CONUS early next week. Periodic shortwaves in a warm/moist sw flow
developing ahead of the western CONUS trough will bring more rounds
of showers into the area early to mid next week. The first of these
shortwaves moves through late Sun night into Monday bringing the
initial batch of showers and isolated t-storms for early next
week. Models show this system tapping into Gulf moisture with
PWATs increasing to around 1.5 inches by midday Monday. This
increase in moisture along with increasing isentropic ascent
should lead to widespread wetting rain across much of the cwa.
Ensemble probabilities show much of the area (except maybe the
tip of the Keweenaw) with a 40-60% chance of seeing 0.5 inch of
rain from this system with the greatest chances south central.
After a period of drier weather Monday night into Tuesday
morning, the next shortwave moves through Tuesday afternoon into
Wednesday spinning up a 985-990 mb sfc low which tracks over
the far western portion of the fcst area late Tue night into
Wed. With PWAT values again increasing to nearly 1.5 inches
along with increasing isentropic ascent, PVA and upper
diffluence fcst with the shortwave, expect widespread rainfall
across the area. EPS probabilities again show a 40-60% chance
for getting half an inch of rainfall from this system with the
greatest chances southeast and west.

Despite the midweek system lifting north and east of the area,
models indicate wraparound moisture behind it could support
lingering isolated to scattered showers for late week (Thu-Fri) as
temperatures trend cooler than normal.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 713 AM EDT Sat May 18 2024

VFR will prevail thru this fcst period at IWD/CMX/SAW. An
approaching cold front will lead to a 2-4hr window for rain showers
beginning at IWD and CMX by early evening at reaching SAW after 00z.
Some thunder will be possible, especially at IWD and CMX. Expect
gusty southerly winds today with gusts of 20-30kts possible.

&&

.MARINE...
Issued at 325 AM EDT Sat May 18 2024

Stable conditions will lead to light winds of generally 20 knots or
less prevailing over the lake into early next week, except for some
20-25 kt southeast gusts today over the east half ahead of an
approaching cold front. Thunderstorms are possible today into
tonight as the cold front marches across the lake. These storms may
contain small hail, gusty and erratic winds, and frequent lightning.
More thunder chances return late Sun night into Monday and then
again late Tuesday into Tuesday night as a series of disturbances
track northeast across the Upper Great Lakes region. Models and
ensembles indicate winds will ramp up Tue night into Wed as a
stronger low pressure center tracks across the western and northern
portions of the lake. Ensemble probabilities show a 40-60 pct chance
of gale force gusts to 35 knots late Tue night into Wed across
western and northern sections of the lake.

&&

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

&&

$$

UPDATE...
SHORT TERM...LC
LONG TERM...Voss
AVIATION...LC
MARINE...Voss