Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 181929
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
329 PM EDT Mon Mar 18 2024

.KEY MESSAGES...

- Lake effect snow winds down this afternoon.
- A quick burst of snow showers goes through the U.P. tonight.
  We could see a dusting near the state-line and along Lake
  Michigan up to a fluffy inch in the Keweenaw and possibly the
  north central.
- Lake-effect snow starts up again over the area Tuesday,
  possibly going into Thursday.
- Blustery winds return Tuesday into Wednesday.
- Northwest high-end gales and heavy freezing spray expected
  Tuesday night and Wednesday across central and eastern Lake
  Superior.
- Another shot for snow comes Thursday night/Friday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 241 PM EDT Mon Mar 18 2024

Radar and satellite imagery show the lake-effect snowfall ending
across Upper Michigan this afternoon, with ridging building in from
the west already bringing partly cloudy skies to Ironwood as of 2 PM
EDT. As this occurs, we could see some additional clearing over the
western U.P. this afternoon, which may raise temperatures a little
bit more than what I forecasted this morning. Nevertheless, with
another shortwave quickly digging down from northern Manitoba this
afternoon to Lake Superior Tuesday morning, expect to see some light
snow showers quickly move across the U.P. tonight. There could be
some moderate snow showers at times, particularly over the west and
north central (see the 12z HREF mean hourly snowfall rates for
reference). Therefore, we could see another dusting from the
Wisconsin border to the Lake Michigan shoreline to a fluffy inch
over the Keweenaw and maybe north central before 8 AM EDT Tuesday.
With temperatures getting into the low to mid 20s tonight and with
winds being lighter than what we`ve seen the previous couple of
days, we could see roads become slick in spots again for the morning
commute Tuesday. Therefore, be a little extra cautious Tuesday
morning, and watch out for some slick spots. As the cold air
advection behind the shortwave begins to work its way into the west
late tonight/early Tuesday morning, we could see some lake-effect
snow start up again over the northwest snow belts (see the 12z
NAMNest) (20% chance).

&&

.LONG TERM /TUESDAY THROUGH MONDAY/...
Issued at 329 PM 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. Through the midweek period, 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 prove
favorable for another 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. At the same time, 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, but is increasing in
regards to a a quick hitting system Thursday night/Friday.

Light snow continues Tuesday courtesy of a passing clipper system,
gradually changing over to lake effect snow as the associated cold
front moves through during the afternoon. 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 setting up persistent NW flow
over the Great Lakes. 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 below the cloud base, 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. Ensembles show a 60-90% chance a widespread 1-2 inches of snow
across the NW wind snow belts by Wednesday afternoon, and while
higher embedded amounts would be expected where we can see some
terrain enhancement as well as throughout the eastern UP courtesy of
the longer fetch off of Superior, exact amounts remain uncertain.
This will bear monitoring, as we could be flirting with advisory
amounts out there. 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 later Wednesday night, 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. This could touch off some light
snow across the area, though our best chances will be across the
southern UP.

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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 132 PM EDT Mon Mar 18 2024

As the lake-effect snowfall ends across the area this afternoon, we
will see improvements to VFR conditions this afternoon into early
this evening, beginning with KIWD in an hour or so. KCMX and KSAW
lift up to VFR near sunset due to the lake-effect clouds stubbornly
holding on over these spots. However, with another shortwave low
moving through Lake Superior Tuesday, a quick burst of snow showers
is possible tonight, mainly over KCMX and KSAW (KIWD may only get a
glancing blow); this burst of snow could drop conditions down to
MVFR/IFR over these two terminals tonight. As we head into Tuesday,
some lake-effect cloud cover and snow showers could bring MVFR
conditions back across the TAF sites.

While LLWS is not expected tonight, there is a very small chance
(<10%) that it could occur at KCMX and KSAW and a slightly better
chance over KIWD (20 to 30%). However, I`m thinking the some of the
gustier winds will mix down to the sfc by KIWD tonight, alleviating
LLWS concerns over there.

&&

.MARINE...
Issued at 329 PM EDT Mon Mar 18 2024

Winds gradually backing more to the W and eventually SW fall back
largely to around 20 knots across the lake this evening, but will
increase to around 20 to 30 knots across the western half of Lake
Superior into the early hours of Tuesday. Another system moving
through the region Tuesday through Wednesday 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 a 30-50%
chance for gales beginning by Tuesday evening, then a 50-80% chance
for high end gales beginning Tuesday night. There is a low chance
(<25%) for storm force winds as well. Given this level of
confidence, a Gale Warning is in effect for much of Lake Superior
Tuesday evening through Wednesday evening. 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 before increasing to around 20 to 25 knots Saturday.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 8 PM EDT /7 PM CDT/ Tuesday to 2 PM EDT /1
    PM CDT/ Wednesday for LSZ240>248-263>265.

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

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

  Gale Warning from 8 PM Tuesday to 11 PM EDT Wednesday for
     LSZ249>251-266-267.

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

Lake Michigan...
None.

&&

$$

SHORT TERM...TAP
LONG TERM...LC
AVIATION...TAP
MARINE...LC


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