Lake Vermilion Area Weather – March 12-14

KEY MESSAGES

– Warm temperatures are expected, approaching or breaking warm low/high records.
– Light wintry mix will be possible on Thursday morning along and north of the Iron Range.
– A strong low pressure system arriving Friday will bring a messy variety of weather conditions, including thunderstorms, accumulating snow, freezing rain, nuisance flooding, and strong winds.

DISCUSSION

Issued at 300 PM CDT Wed Mar 12 2025

Near Term (Today through Thursday Night): Fairly quiet conditions
are expected today through tomorrow night as the 500mb pattern
shifts to ridging. A weak shortwave trough will propagate through
Thursday morning into the early afternoon bringing increased clouds
and a chance for light rain/snow along and north of the Iron Range.
Total snow amounts are expected to be a dusting up to a tenth or
two. Temps will be warm tomorrow, especially for the southern half
of the CWA, where highs will reach the upper 50s to low 60s.

Messy Late Week into Weekend Spring Storm: A deep 500mb trough
currently over the Pacific Ocean is expected to arrive onshore along
the West Coast late tonight into Thursday morning. As this trough
propagates east, a Colorado Low/Panhandle Hook type system will
undergo cyclogenesis Thursday night into Friday morning. This low
pressure will quickly move into the Upper Midwest with an
anticipated arrival of the low pressure center into the CWA being
around midday Saturday. By the time this low pressure enters the
CWA, this will be a messy vertically-stacked Spring system, with
nearly all precip-types on the table. Given the complexities of this
late week/weekend system, hazards and weather types are broken down
below.

Thunderstorm Potential (Friday into Friday evening): One of the
first concerns with this upcoming low pressure system will be the
potential for isolated strong to severe thunderstorms. A warm front
will be lifting north across the CWA Friday morning, with southerly
flow bringing ample WAA and moisture advection to the area. High
temps on Friday will be near or even record breaking across the CWA
with temps in the mid 50s to upper 60s. These unseasonably warm
temps are expected to be combined with favorable dewpoint temps near
50 degF as Gulf moisture is advected north.

This moisture combined with moderately steep mid-level lapse rates
around 7-8 DegC/km will bring a chance for MLCAPE to increase into
the 600-1000 J/kg range, mostly in northwest WI and adjacent
counties in MN where the warm sector will be most pronounced.
With 0-6km bulk shear of 30-35 knots, isolated strong to severe
thunderstorms cannot be ruled out for Friday afternoon and
evening with all severe weather hazards possible. There are
still a lot of potential failure modes for convection that
increase uncertainty at this time, most notably a warm nose
around 750-800mb creating 50-100 J/kg of CIN. If this cap
remains in place, it could limit the potential for damaging
winds or a tornado as storms remain elevated. Given the
uncertainties at this time, the CWA is still under a General
Thunder outlook from SPC. However, this will be something to
closely monitor as we head closer to Friday.

Rain and Minor Flooding Potential (Friday Through Saturday): In
addition to the potential for thunderstorms on Friday, there will
also be a fair amount of widespread precipitation across the CWA.
Southerly flow will bring plentiful moisture advection with PWAT in
the 0.75-0.9″ range, which is up to the 99th percentile of NAEFS
climatology. As the Colorado Low propagates through, expect multiple
rounds of rain on Friday through Friday night. This will be
transitioning to snow and/or a wintry mix from west to east on
Saturday as the cold sector advects into the CWA. 48 hour QPF ending
12z Sunday from the NBM 50th percentile is around 0.5-1.0″, which
could lead to minor nuisance flooding impacts such as ponding in low-
lying areas. Since frost depth remains deep across the CWA, little
infiltration is expected and most of the rain this weekend will be
runoff.

Snow and Freezing Rain Potential (Saturday into Sunday Morning):
Starting on Saturday, the cold sector associated with this weekend`s
system will begin to advect into the CWA. As this sub-freezing
airmass moves from west to east across the area, this will introduce
the potential for messy precip-types through the day Saturday. One
concern at this time is the potential for an hour or two of freezing
rain on Saturday as temps at the surface drop below freezing and a
warm nose around 825-850mb persists. Ice accumulation probability is
fairly low at this time from the NBM at a 20% chance in the far
western CWA. Current expectation is that the transition from rain to
snow on Saturday will be fairly quick and any ice accumulation will
be around a glaze to a hundredth or two of an inch.

As for snow potential, amounts are likely to be on the lighter side
in our CWA with 3 inches or less of accumulation forecast. Highest
amounts with this weekend`s system are expected to be underneath the
trowal where moderate to heavy banded snow may develop. Current
guidance from the 12z GFS shows the enhanced area of FGEN, negative
omega, and deep moisture will be west of the CWA near the Red River
Valley. Therefore, this will keep highest snowfall totals west of
the area, with only the far western CWA getting up to 3-4″. Expect
lesser amounts of an inch or less farther east. Ensemble MSLP
centers have been fairly consistent in recent runs, which increases
confidence that this band of heavier snow will remain just outside
of the CWA. However, this will be another feature to keep a close
eye on. Expect snow to exit the area by Sunday afternoon.

Strong Winds and Fire Weather Concerns (Saturday night into Sunday):
Much colder and drier air advects into the CWA Saturday night
following the cold frontal passage and the propagation of this
weekend`s system downstream. Breezy northwest winds combined
with strong CAA may result in strong katabatic winds in the lee
of the higher terrain along the North Shore. Current forecast
expectations are gusts up to 40-45 mph along the North Shore. If
trends hold and/or winds increase slightly, a Wind Advisory may
be needed Saturday night in southern Lake and Cook Counties.
Fire weather concerns may also enter the picture on Sunday as RH
drops near 30% and winds remain breezy. Fortunately, moisture
from this weekend`s system may help mitigate fire concerns as
fuels receive plentiful moisture.

AVIATION

Issued at 1234 PM CDT Wed Mar 12 2025

VFR conditions expected for most of the period. A weak low pressure
system moves through tomorrow morning, bringing an increase in cloud
cover and the potential for snow showers and/or a wintry mix to
far north-central MN and the Arrowhead. A MVFR visibility
reduction will be possible for INL tomorrow morning due to light
snow. HIB may also be impacted by light snow, but confidence is
lower. Winds will be light and variable for much of the TAF
period.

MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR

Issued at 300 PM CDT Wed Mar 12 2025

Light and variable winds will continue over western Lake
Superior tonight through Thursday morning. Northeast gusts up to
20 kts and waves to 3 ft near the head of the lake is expected
on Thursday afternoon into Thursday night from tightening
pressure gradients ahead of the late week into the weekend
system. Looking ahead, strong northwest winds are expected
across western Lake Superior on Saturday night into Sunday with
a low 20% chance for gales along the North Shore on Saturday
night due to downslope winds in the lee of the higher terrain.
Small Craft Advisories and a possible Gale Watch/Warning may be
needed.

For the open water discussion, refer to the NWS Marquette Area
Forecast Discussion at weather.gov/mqt.

WATCHES/WARNINGS/ADVISORIES

MN…None.
WI…None.
MARINE…None.