Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 230741
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
341 AM EDT Sat Mar 23 2024

.KEY MESSAGES...


- Late season winter storm lifting northeast from Colorado early
next week brings accumulating snow and hazardous travel late Sunday
into Monday.
- Westerly lake effect snow mainly for the Copper Country Wednesday
and Wednesday night.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 313 AM EDT Sat Mar 23 2024

Water vapor imagery and RAP analysis show mid-level troffing over
central and eastern Canada, anchored by a deep mid-level low
centered on the Hudson Bay shore of Ontario. In the wake of a weak
shortwave that passed, modest caa is underway with 850mb temps
across Lake Superior currently ranging from roughly -15C e to -17C w
per latest RAP analysis. Models have been advertising that a sfc
trof would drop across the lake during the night, and that is in
fact the case. KMQT radar shows band of mdt/hvy shsn along the wind
shift that is approaching the shoreline of n central Upper MI. It
also appears that a mesolow is trying spin up along the trof to the
n of Munising. Away from the convergence along the trof, LES is
struggling due to dry air. 00z KINL sounding showed a very hostile
environment for LES with a pronounced inverted-v profile blo 800mb
in what is also a very dry column overall. The hostile for LES
inverted-v profile becomes typical at this time of year due to
increasingly higher sun angle/solar insolation and resulting
deepening mixing during the daytime. With the dry air, there`s even
not much in the way of cloud cover off of western Lake Superior.
With mostly clear skies dominating much of the area, temps are
approaching 0F at traditional cold spots across the interior w half.

A quick burst of mdt/hvy shsn will accompany sfc trof as it pushes
onshore in the next couple of hrs, mainly affecting Alger County.
Thereafter, expect isold to sct -shsn and flurries thru the day
across the n central and eastern fcst area. Looks like kind of a
hybrid type LES scenario where daytime heating working on the
moisture fluxes advected off of the lake aid land based shsn
development. This should be most apparent over Marquette County
where developing lake breeze will also aid low-level convergence.
Out w, the very dry air mass will prevent anything more than sct
flurries and maybe a few -shsn thru early to mid aftn. Expect highs
today in the mid 20s to lwr 30s, warmest s central.

Any lingering flurries should end by sunset. Sfc high pres arriving
over the area late aftn/evening will drift e tonight, resulting in
light se to s winds developing overnight. With 850mb temps across
northern Lake MI around -12C, some flurries may develop into
portions of central Upper MI late tonight. For now, left mention out
of fcst.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 339 AM EDT Sat Mar 23 2024

The primary forecast challenge continues to be the impending wintry
mess late Sunday into Monday ahead of a Colorado low lifting
northeast across western Lake Superior on Tuesday. Wintry precip
transitions to rain on Monday that persists through Tuesday before
transitioning back to snow late on Tuesday. Lake effect potential
- mainly for west wind snow belts - develops on Wednesday before
tapering off Thursday. Above normal temperatures and synoptic
precipitation chances return late next week.

Beginning with Sunday morning, a ~1030 mb surface ridge positioned
across southern Ontario results in increasing southeasterly flow.
Upslope SE flow off Lake MI results in increasing low level
cloudiness and chances for light snow, mainly across higher
elevations of the western UP. Much of the cloud-bearing layer and
modeled lift resides in a deep DGZ with light low level winds
implying initially high SLRs. However, surface temps warming to
around freezing and relatively strong late March sun suggests minor
travel impacts until heavier precipitation arrives later on Sunday.

An impressive warm front lifts across Upper Michigan Sunday night
with a band of heavy precipitation rates developing within strong
isentropic ascent and frontogenesis along and north of the warm
front. As the heavier precip rates arrive late on Sunday, the DGZ
narrows and raises to roughly 12-16 kft AGL. Not only is this
positioned above the best forcing for ascent, but there also appears
to be considerable turbulence below the DGZ suggesting potential for
dendrite fracturing. All that is to say that even though there may
be a brief window of high SLR snowfall early in the event, I expect
SLRs closer to 10:1 for the bulk of the QPF and I edited the
forecast accordingly. Speaking of QPF, ensemble means advertise
a considerable west-to-east gradient due to a dry slot along and
south of the warm front. Ensemble means advertise up to 3/4" of
QPF across the western UP to less than 1/4" across the eastern
UP by 12z Monday when p-type issues arise. This gradient should
be even sharper in reality, but there`s uncertainty in where the
gradient sets up with the GEFS/CMCE noticeably farther east
than EPS guidance. There may also be some southeasterly lake
enhancement on the Keweenaw. In addition to instigating a QPF
gradient, the dry slot also delineates the first (all snow) and
second (wintry mix) waves of precipitation.

Monday`s forecast is tricky with meaningful model differences as the
low pressure approaches being vertically stacked/occluded over
northwestern Iowa. Model guidance is in good agreement that a
shortwave ripples northeast along the warm front draped across our
area resulting in considerable p-type challenges. This waves brings
light to locally moderate QPF with the best chance for all snow
being on the Keweenaw. With the surface low displaced well to the
southwest, stable low levels, and generally easterly flow makes me
skeptical of the magnitude of warming on Monday. While the RGEM is
most aggressive with Monday`s snow potential, the prospect of
accumulating snow persisting through Monday afternoon across
the northwest 1/3 of the U.P. shouldn`t be immediately
discounted. On the other hand, NAM guidance shows a sharp
boundary layer inversion with a warm nose aloft that raises
IP/ZR concerns. Regardless of the model, a northwest to
southeast gradient in QPF and p-type seems likely to cause
forecast issues on Monday.

Warm air advection eventually overwhelms the entrenched cold air
mass on Monday leading to a period of rain that continues until the
systems cold front moves through late on Tuesday. Importantly, an
energetic shortwave rounds of the base of the trough on Monday then
accelerates northeast toward the Great Lakes region Monday night and
Tuesday. This negatively tilted shortwave results in a renewed
period of cyclogenesis and intensifying precip as the low pressure
tracks across western Lake Superior on Tuesday. This wave of precip
appears to fall exclusively as rain and ensemble means advertise
another wave of locally moderate precip with the heaviest amounts
downwind of Lake Michigan. The cold front sweeps across the area
Tuesday night changing any lingering precip back to snow. The 12z
grand ensemble also shows probabilities of 850 mb temps cooling
below -11C increasing above 50% Tuesday night through Thursday
afternoon. This is sufficiently cold for lake effect snow and models
are in seemingly good agreement about LES mainly for the west wind
snow belts.

Another trough moves over the Pacific Northwest on Thursday that
emerges on the Plains on Friday. Ridging building ahead of this
system results in temps warming above normal on Friday then
precipitation chances returning on Saturday. Ensembles suggest the
trough and associated surface low weaken while approaching the area
suggesting mainly light precip amounts. The forecast low track near
or south of the UP indicates some wintry p-type potential, but it
doesn`t seem like it`s worth getting excited about at this time.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 121 AM EDT Sat Mar 23 2024

Conditions have trended to VFR at IWD/CMX/SAW. There could be
another round of lake effect showers developing overnight into
today with a push of colder air moving across Lake Superior.
These showers could drop conditions back down to MVFR at some of
the terminals late in the night and today with the best chance
of MVFR conditions occurring at SAW under a weak northerly flow.

&&

.MARINE...
Issued at 339 AM EDT Sat Mar 23 2024

North winds around 20-25 knots are occurring across most of Lake
Superior early this morning as a colder air mass flows across the
lake. Winds diminish to mostly under 15kt on Saturday as high
pressure builds over the lake. A deep low pressure develops over
eastern CO on Sunday and tracks across the western lake on Tuesday.
Ahead of the low pressure, SE to E winds increase to 20-30kt by late
Sunday afternoon, strongest across the western lake. Winds of 20-
30kt are expected across much of Lake Superior Sun night through
Monday night with gale potential increasing to 70-90% by Mon morning
- highest across western Lake Superior. Easterly gales of 35-40kt
are expected for Mon/Mon night, with 40-60% chance for high-end 40-
45kt gales. East winds diminish as the low pressure lifts across
western Lake Superior on Tue, but west winds increase as a much
colder air mass moves across the lake. West winds up to 30 kts are
expected late Tuesday night into Wednesday night as the low pressure
lifts north of the lake.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Watch from Monday morning through late Monday night for
     LSZ162-243>245-251-263-264-266-267.

  Small Craft Advisory until 8 AM EDT /7 AM CDT/ this morning
     for LSZ240.

  Small Craft Advisory until 10 AM EDT /9 AM CDT/ this morning
     for LSZ241>243.

  Small Craft Advisory until noon EDT today for LSZ244.

  Small Craft Advisory until 2 PM EDT this afternoon for LSZ248-
     251.

  Small Craft Advisory until 4 PM EDT this afternoon for LSZ249-
     250.

Lake Michigan...
None.

&&

$$

SHORT TERM...Rolfson
LONG TERM...EK
AVIATION...Voss
MARINE...EK


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