677
FXUS63 KMQT 101127
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
727 AM EDT Thu Oct 10 2024

.KEY MESSAGES...

- Dry weather until Friday as high pressure shifts east over the
  Great Lakes.

- A cold front dropping through Friday will bring our next
  chances for rain showers, as well as cooler temperatures in its
  wake for the rest of the forecast period.

- Lake effect/enhanced rain showers become likely again late weekend
  into early next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 327 AM EDT Thu Oct 10 2024

GOES-16 Nighttime Microphysics RGB imagery shows clear skies over
Upper Michigan except for patches of fog over the Keweenaw
Peninsula, Marquette/Baraga highlands, and over eastern Luce
County at 03Z. This fog has been dense at times with visibility
dropping to a quarter mile at times at the NWS Marquette office
in Negaunee Township. However, given the lack of more widespread
coverage, elected not to go with a product at this time. High
pressure of 1022 mb is shown in the RAP analysis over the
Straits of Mackinac with pressure over 21020 across virtually
the entire Great Lakes basin, allowing for efficient radiational
cooling over the UP. Freezing and sub-freezing temperatures
have already been seen at multiple different sites including
KSAW, KESC, and KERY and sub-freezing lows should continue to
expand across much of the UP away from the Great Lakes.

Ridging aloft will remain over the area through today and tonight.
Consistent warm advection will allow for highs to climb to near 60
in the east and near 70 in the west today. The warm advection will
keep Friday morning lows from cratering like in previous nights,
with MOS guidance suggesting lows around 50, much warmer than the
lows near freezing from the past couple days. Winds will begin
picking up overnight as a cold front approaches the western UP near
12Z Friday, compressing the pressure gradient. The HREF mean wind
gust potential is around 35 mph Friday morning, and while this
forecast will not reflect values quite that high, it will be a
notable change from the relatively lighter winds during the day
today. One other note will be that skies wont be completely clear
during the day today as wildfire smoke from the western US will
drift over the Great Lakes by this evening. Near-surface smoke/haze
is not forecast as the smoke should be fairly elevated, but this
will still cause some less blue skies and might dampen the high
temperatures today by a degree or two.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 436 AM EDT Thu Oct 10 2024

Beginning Friday, a series of shortwaves emerging from the Pacific
NW States and British Columbia/Alberta early this morning as noted
on water vapor imagery will continue east-northeast across
Saskatchewan and northern Manitoba today reaching Hudson Bay and
northern Ontario later this evening. As the developing shortwave
trough and associated sfc trough extending south from northern
Hudson Bay dives east-southeast across northern Ontario on Friday it
will push a cold front across the CWA during the daytime hours. This
moisture-starved system with ensembles still showing PWATs around
0.9in, or near the climatological mean value for the area, will
probably not produce anything more than isolated to maybe scattered
light showers, especially given that the best forcing/dynamics with
the system will be well north into Ontario as the front passes
through. Ensemble guidance suggests the best chance for measurable
rainfall (30-50%) over mainly the east half on Friday afternoon
where CAA from winds shifting northwest behind the front over
eastern Lake Superior combined with weak forcing along the frontal
boundary and the longer fetch across the eastern lake could account
for the higher probability of getting greater than 0.01 inch of
rainfall. Expect well above normal temps along and ahead of the
front on Friday with highs generally in the upper 60s to lower 70s.

Expect mostly dry conditions Fri night into Saturday as CAA (850 mb
temps drop 0-2C) behind the front probably will be not cold enough
to support pure lake effect showers during this period due a sharp
transition to sfc ridging from the nw and a much drier anticyclonic
nw flow as noted off fcst soundings. However, conditions quickly
become more favorable for lake effect/lake enhanced pcpn by late
weekend (especially late Sat night into Sunday) as model consensus
suggests a cyclonic ~130 kt upper jet max digging through the
Northern Plains into the Upper Midwest along with a series of
clipper shortwaves. This jet max and associated shortwave energy
will help carve out a fairly broad mid-level trough late Saturday
into Sunday which will envelop the Upper Great Lakes region into
early next week. Models also indicate double-barrel mid-level low
circulations forming within the broad trough with one forming over
southern Hudson Bay/northern Ontario Sat night into Sunday and a
second one developing near eastern Ontario/southwest Quebec late
Sunday. How these circulations evolve within the broad trough will
likely have an impact on our weather late weekend into early next
week, although exact model details with these features is still a
bit hazy at this point. At any rate by late weekend, models indicate
a tightening gradient and north winds setting up on the backside of
the low developing to the east. These north winds will pull colder
air across the Upper Great Lakes sending 850 mb temps down to as
cold as -5C to -7C late Sun night into Tuesday. The CAA combined
with mid-level forcing from the lows or shortwaves moving across the
region will provide a very favorable setup for more sustained north
wind lake effect rain showers beginning probably late Sat night and
continuing into Tuesday. With models also indicating a 500 mb cold
pool with temps of -30C or colder moving overhead at mid-levels late
weekend into into Monday, the supported corresponding deep
instability is reflected in the fcst model soundings with soundings
indicating lake-induced CAPEs approaching 1000 j/kg and lake-induced
ELs of nearly 25kft! This deep overwater instability could support
waterspout formation over the Great Lakes late weekend into early
week while also supporting moderate to heavy lake effect rain
showers and possibly graupel showers at times downwind of Lake
Superior. Models are in good agreement showing sharp ridging and
subsidence from west leading to lake effect showers ending and drier
conditions Tue night into Wednesday.

Regarding temps behind Friday`s cold frontal passage...expect
Saturday`s highs dropping closer to normal with mid 50s to lower 60s
expected. Temps will then trend below normal for the late weekend
into early next week with highs Sunday generally ranging from the
upper 40s north to mid 50s south and highs Monday and Tuesday
ranging from the mid to upper 40s north to lower 50s south under a
rainy, moist, cool upslope/onshore flow. With the ending of lake
effect showers and possible clearing and lighter winds from the sfc
ridge axis approaching could lead to an especially chilly night Tue
night, especially over the western interior where the lower end of
model guidance suggests the potential of lower 20s to possible upper
teens readings. Wednesday`s high temps should moderate closer to
normal and perhaps a bit above with mid to upper 50s readings under
abundant sunshine.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 726 AM EDT Thu Oct 10 2024

VFR conditions are expected throughout the entire period for IWD and
CMX, and SAW will be VFR once the morning FG ends. Model guidance
has not handled the occasional FG at CMX and SAW well overnight and
thus, predicting cessation of FG at SAW is a bit tough, but have
decided to go with a TEMPO through 14Z to reflect the increasingly
patchy/shallow nature of the FG. As a cold front approaches from the
west by Friday morning, winds will increase out of the southwest
throughout the day today and tonight. A LLWS threat exists at all
sites around 06Z as relatively lighter winds at the surface are
contrasted with a 40-45 kt low level jet at 1,500-2,000 ft which is
also at the top of the inversion, with LLWS decreasing between 12Z
and 15Z Friday.

&&

.MARINE...
Issued at 436 AM EDT Thu Oct 10 2024

Southeast winds coming in below 20kts early this morning become
southerly up to 20-25 knots this afternoon, highest east half. As a
cold front approaches from the west, southwest winds increase to 25
knots over the west half late Thu night and then with the frontal
passage on Friday shift northwest. A few of the models suggest a
better chance for gales to 35 kts over the eastern 2/3rds of the
lake Fri afternoon into Fri evening which is supported by fairly
strong cold advection and a rapid rise in pressure behind the front.
As a result, decided to issue a Gale Watch Fri afternoon into
evening for LSZ264-267 and adjacent NSH zones. Expect winds to
quickly diminish blo gales by late Fri evening and should diminish
blo 20 kts late Friday night into Saturday as high pressure briefly
builds over the region. A stronger deeper system, likely with higher
winds potentially reaching gales, is expected later in the weekend
into early next week, most likely beginning late Saturday night and
continuing into Monday. The cold air associated with this system and
associated deep overwater instability could also lead to the
potential for waterspout formation of Lake Superior Sunday into
Monday given the relatively warm lake temps still in place. ECMWF
ensembles indicate a 50-60% potential for northerly gale gusts to 35
kts at times late Sunday into Sunday evening. Expect the northerly
gradient winds to weaken to 20-25 kts heading into early next week as
a high pressure ridge again slowly builds in from the west by
midweek.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Watch from Friday afternoon through Friday evening for
     LSZ243>251-264>267.

Lake Michigan...
None.

&&

$$

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