Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180719
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
319 AM EDT Mon Mar 18 2024

.KEY MESSAGES...

- Lake effect snow winds down today along with the wind
  diminishing.
- Clipper brings a wave of light snow Monday night and Tuesday
  morning, followed by lake effect snow event through early
  Thursday.
- Blustery winds return Tuesday night and Wednesday.
- Northwest high end gale force winds and heavy freezing spray possible
  Tuesday night and Wednesday across eastern Lake Superior.
- Another shot for snow comes Thursday night/Friday.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 301 AM EDT Mon Mar 18 2024

Upper air pattern consists of a 500 mb trough and closed low over
the desert sw and a ridge over the Pacific NW with a deep trough
over the eastern U.S. The deep trough moves east and narrows over
the eastern U.S. today with upper ridging starting to move into the
upper Great Lakes by 00z Tue. DGZ continues to be in the cloud layer
below the inversion which is at 5000 feet, but inversion falls today
below 3000 feet, so until the wind backs to the west and southwest
which is late this afternoon, the light snow showers will continue,
but pops will decrease. This is covered well in the forecast, but
did hang on to pops longer in the west and the Keweenaw as models
tend to end it quicker than what actually happens.

&&

.LONG TERM /TONIGHT THROUGH SUNDAY/...
Issued at 318 AM EDT Mon Mar 18 2024

Not much has changed in the past 24 hours with respect how guidance
is projecting the eventual evolution of the pattern across North
America. Early this week, the main setup will involve a broad
ridge/trough pattern from west to east across the continent,
positioning the forecast area in northwest flow. This will favor us
for any clipper system diving out of Canada, opening the door for
snow chances, more winter like temperatures, and gusty winds. Toward
the end of the week and weekend, the broad trough over the eastern
third of North American will lift and longitudinally stretch across
Canada. Coincidentally, an eastward progressing deep trough will push
into the west coast. There appears to be a slowing trend in the west
coast troughing, which appears to be a factor into a potential storm
early next week. Overall though, confidence in the latter half of
this forecast period is low (25%), but is increasing in regards to a
a quick hitting system Thursday night/Friday.

Tonight, a clipper will ride the northwest flow road down into the
Upper Great Lakes with preceding weak warm air advection spreading
over the region. As the low inches closer, 850mb temps warm to -10
to -8C while a swath of isentropic ascent enables light snow to
spread southeast across Upper Michigan. Across the west, snow
potential appears to begin this evening but ends overnight. A little
later start to the snow is expected in the east, mainly after
midnight. Expecting light snow to be possible through the day
Tuesday before the clipper`s cold front swings through. The bulk of
the cold air isn`t expected to surge in until Tuesday evening as a
secondary shortwave presses in. This will enable 850mb temps to
plummet to near -20C by Wednesday morning. As the surface low pulls
away into southern Ontario/eastern Quebec, stout high pressure will
press southeast out of the Canadian Prairies. Together, all of this
will kick off another lake effect snow episode and blustery winds
Tuesday night and Wednesday. Model soundings show lift co-located
with the DGZ and inversion heights upwards of 7k feet. But they also
include an inverted V signature, indicative of a dry near surface
layer that will need to be overcome for significant snow
accumulations. Models vary on the impact this could have on the
snow, so confidence in the forecasted accumulations is low (25%).
Guidance does suggests the longer fetch going into eastern Upper
Michigan will provide the more favorable environment for
accumulation. Expect snow showers to linger across the east into
early Thursday, but end Wednesday afternoon or evening in the west.
The resulting strong pressure gradient between the low and high and
cold air advection will provide an ideal environment for blustery
winds. Daytime heating during the day Wednesday will enable more
widespread blustery conditions. Right now, 30-40 mph northwest winds
are expected near the lakeshores, with 25-35 mph possible elsewhere.
The strong winds may also support some beach erosion/lakeshore
flooding concerns for Alger and Luce counties during the day
Wednesday.

As this system pulls away, a closed low will drop into Hudson Bay
while a weak middle stream shortwave presses due east across the
north-central Plains and a southern stream into the Deep South. On
Friday, a slug of isentropic ascent tied to a weak warm front
associated with the middle shortwave will stretch eastward into the
Upper Midwest. Between last night and tonight`s guidance, a more
northern solution appears favored for any over running snow Thursday
night and Friday. While confidence is still low (25%) at this point,
a round of light snow is looking more possible.

This weekend, guidance suggests a deep and potent shortwave will
begin organizing and lift out of the Rockies. As expected this far
out, there`s considerable spread among the ensemble systems on its
track and where the warm/cold air will be; but given the spread in
possibilities, its recommended that anyone with travel plans Sunday
into early next week keep tabs on the forecast.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 116 AM EDT Mon Mar 18 2024

Ongoing lake enhanced snow off of Lake Superior is diminishing and
will continue to do so overnight as a drier air mass begins to
overspread the area. That said, lake effect shsn/flurries won`t
completely end until passage of sfc high pres ridge today. At IWD,
expect MVFR to prevail thru this morning with -shsn diminishing to
flurries by sunrise. Lingering flurries will end, and MVFR cigs will
clear out to VFR early to mid aftn. At CMX, expect MVFR to prevail
thru today with -shsn diminishing to flurries this morning.
Lingering flurries will end, and MVFR cigs will scatter out to VFR
this evening at CMX. However, next approaching disturbance will
likely bring a period of -sn and MVFR conditions to CMX late
evening. At SAW, MVFR will prevail thru today, though a period of
IFR cigs is possible overnight. Ongoing -shsn will diminish to
flurries this morning, then end in the aftn. The MVFR cigs will
clear out to VFR at SAW this evening.

&&

.MARINE...
Issued at 318 AM EDT Mon Mar 18 2024

Winds will gradually lighten today, but some stray gales this
morning can`t be ruled out. Light winds below 25 knots are expected
by this afternoon that`ll persist through Tuesday morning. Another
system moving through the region then will bring another punch of
colder air and tighter pressure gradient, with the threat for gales
across the east half increasing Tuesday night into Wednesday.
Internal probabilistic guidance shows around 50-80% chance for high
end gales beginning Tuesday night, with a low chance (<25%) for
storm force winds. At this point, opted to expand and move up the
inherited Gale Watch west and up a few hours. Additionally, the
combination of cold air and strong winds, an environment favorable
for heavy freezing spray development is likely (>75%). Winds
decrease Wednesday night, coming in at or below 20 knots the rest of
the week.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Small Craft Advisory until 11 AM EDT this morning for LSZ246-
     247.

  Small Craft Advisory until 2 PM EDT /1 PM CDT/ this afternoon
     for LSZ240>242.

  Gale Watch from Tuesday evening through Wednesday evening for
     LSZ240>251-263>267.

  Small Craft Advisory until 5 PM EDT this afternoon for
     LSZ243>245.

  Small Craft Advisory until 11 PM EDT this evening for LSZ248-
     249.

  Small Craft Advisory until 2 AM EDT Tuesday for LSZ250-251.

Lake Michigan...
  Small Craft Advisory until 11 AM EDT this morning for LMZ221-
     248-250.

&&

$$

SHORT TERM...07
LONG TERM...JTP
AVIATION...Rolfson
MARINE...JTP


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