Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 250221
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
921 PM CDT Sun Mar 24 2024

.KEY MESSAGES...

- A winter storm will bring heavy accumulating snow and a wintry
  mix to the Northland today through Tuesday. Winter Storm
  Warnings remain in effect across the region through Tuesday. A
  Blizzard Warning remains in effect for the North Shore as
  well.

- Snow accumulations in excess of 12 inches are expected for a large
  portion of the area, mainly in northern Minnesota. Ice
  accumulations ranging from a glaze up to two tenths of an inch
  will also be possible, mainly on Monday night into Tuesday
  morning.

- The winter storm will be exiting the area on Tuesday night
  with light snow lingering for some on Wednesday. The remainder
  of the week into next weekend will be relatively quiet with
  temps gradually warming.

&&

.MESOSCALE...
Issued at 920 PM CDT Sun Mar 24 2024

Rest of this Evening - Tonight:

Current radar and observations shows a band of more moderate
snow with visibilities of 0.5 to 1.5 miles extending from the
Brainerd Lakes up into the Twin Ports and east into Ashland and
Hurley. This band has been associated with some weak
frontogenesis and led to snow rates of around 0.5"/hour; the
measurement at the DLH NWS office has been an additional one
inch from 7 PM to 9 PM. However, as this band moves into the
North Shore, orographic and lake enhancement (lake-induced CAPE
of 50-100 J/kg) should lead to moderate to localized heavier
snowfall rates. Along the North Shore, increased snowfall rates
up to 1" per hour will be possible with this snowband during the
remainder of the evening (next 3 hours).

By late this evening through tonight, a stronger synoptic
snowband over southern Minnesota into west-central Wisconsin
will push northward into northwest Wisconsin and eventually
towards the Twin Ports and North Shore towards Monday morning.
Periods of moderate to heavy snowfall (rates of 0.75-1.5"/hour)
will be possible with this band despite generally lower snow
ratios (8-12 to 1) due to strong frontogenetic forcing and
strong isentropic ascent. The highest consistent snowfall rates
will remain along the higher terrain of the North Shore tonight
into Monday morning. Look for 6-hour accumulations between 1 AM
and 7 AM (06Z-12Z) tonight on the order of 3-6 inches in
northwest Wisconsin and the higher terrain of the Twin Ports and
North Shore.

&&

.DISCUSSION...
Issued at 423 PM CDT Sun Mar 24 2024

Today through this evening:

The well-advertised wintry system will be arriving into the
Northland this afternoon/evening and linger through Tuesday. For the
rest of the afternoon, much of northeast Minnesota north of US 2
(excluding the North Shore) is expected to see mainly light snow
with modest accumulations (up to 1-2 inches, with some low-level dry
air entrainment from the north. Further south, the area of
synoptically-forced snow that was over the Twin Cities and vicinity
is expected to continue moving north, leading to an expansion of
light to moderate snowfall from east-central Minnesota into the Twin
Ports and northwest Wisconsin this afternoon and evening.

Weak embedded frontogenesis may result in some locally heavy
snowfall rates approaching 1” per hour at times, but more likely
hovering closer to 0.5” per hour per the latest HREF trends and
current observations. Along the North Shore, increased snowfall
rates up to 1" per hour will be possible this afternoon and evening
due to a combination of orographic and lake enhancement. While delta-
Ts won`t be large enough to support true lake effect snow, lake
induced CAPE around 100-200 J/kg  will still result in localized
areas of moderate to heavy snow this afternoon and evening along the
North Shore.

Tonight into early Monday morning:

The bulk of snowfall associated with the winter storm is expected to
occur tonight through Monday morning. Moisture will be plentiful
tonight into tomorrow morning as this low pressure system taps into
two sources. The first source of moisture will be from a remnant
atmospheric river from the Gulf of California, which will be
advected north as the low propagates northward. The second (and
primary) source of moisture will be coming from the Gulf of Mexico
via a strong southerly 850mb LLJ of around 50 knots.

This northward surge of moisture will also be accompanied by strong
synoptic forcing ahead of a warm, turning quasi-stationary, front
that will be lifting north before stalling over the CWA. One thing
of note is that strong FGEN tonight into tomorrow morning will be
arriving in several waves. This will result in periods of moderate
to heavy snowfall, with the heavier bands of snow being associated
with areas of stronger dynamic forcing. Snowfall rates will be
varying between 0.5-1" per hour through tonight into tomorrow
morning. The most consistent heavy snowfall rates up to 1" per hour
will be found along the North Shore, where lake and orographic
enhancement will occur in east to northeast flow.

Snow accumulations tonight into early tomorrow morning will be
highest southeast of the Iron Range and along the North Shore, with
amounts around 6-12 inches. Northwest of the Iron Range,
accumulations drop off to only 1-2" near the International Border.
This is due to a sizable dry layer near the surface, which will
delay the onset of snow until late tonight.

Winter Storm Warnings remain in effect through Tuesday afternoon.
The Blizzard Warning also remains in effect for southern Lake and
Cook Counties, as winds gusting up to 45 mph will be possible
(especially on Monday into Monday night).

Monday through Monday night:

The low pressure system is expected to become increasingly messy
when it comes to precipitation type starting on Monday morning. An
intrusion of warm air into northwest Wisconsin will begin
transitioning snow to a wintry mix and eventually all rain by late
Monday afternoon. As this transition from snow to rain occurs from
south to north, a period of freezing rain lasting an hour or two is
likely (50-70% chance) on Monday morning. Ice accumulations are
expected to range from a glaze to a tenth. However, above-freezing
temps and rain will likely melt any ice on Monday afternoon.

Based on recent model runs, WAA is likely to bring the warm sector
as far north as the Iron Range and as far west as the Brainerd Lakes
area by Monday evening. This will bring a band of sleet and freezing
rain/drizzle into northeast and north-central Minnesota on Monday
afternoon through Monday night. Model soundings show that a period
of several hours of freezing rain will be possible (60% chance) as
the warm nose works it`s way north. A weak dry slot is also likely
to enter the CWA on Monday, which could also enhance ice
accumulations via freezing drizzle. Highest ice accumulations are
expected around a line from Isle, MN to Duluth/Cloquet and north
into the Arrowhead towards Grand Portage, MN. Ice amounts along this
line will be around 0.1-0.2". Locally higher amounts up to 0.25" may
be possible, but confidence in anything beyond 0.2" of ice is low.

In addition to the ice potential on Monday and Monday night,
additional snow accumulations of 3-8" are expected in northeast
Minnesota. Most of the snow on Monday and Monday night will occur
northwest of a line from Brainerd to the Iron Range, where sub-zero
temps are expected to linger the longest.

Tuesday into Wednesday:

Precipitation type will be transitioning back to snow on Tuesday as
the cold sector shifts eastward. By the time the cold sector engulfs
the CWA, the majority of QPF associated with this system will have
fallen. Therefore, additional accumulations on Tuesday into
Wednesday are expected to be around 2 inches or less. Expect the
winter storm to exit the CWA on Tuesday night. Lingering light snow
in the Arrowhead and far north-central MN will be possible through
Wednesday.

Wednesday into Next Weekend:

Lake-effect snow will be possible on Wednesday night along the South
Shore in north-central WI as northwest to west flow occurs along
with cool 850mb temps. Thursday will likely be quiet as a ridge
builds over the CWA. The next chance for a wintry mix arrives on
Friday and lingers into Saturday as a clipper enters the upper
Midwest. High temps on Friday into next weekend will be warming into
the upper 30s to mid 40s.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 623 PM CDT Sun Mar 24 2024

Mainly seeing MVFR to IFR ceilings with IFR to LIFR visibilities
in light to moderate snow across much of the Northland as of
2315Z. Conditions become LIFR to VLIFR for a period tonight
through Monday morning, particularly at HYR as a strongly forced
frontogenetic band of snow with rates up to 1-1.5 in/hr advects
north into NW WI between about 04Z-07Z. Overnight, heavy
snowfall rates will lead to half mile or less visibility at
times in the Northland. East to northeast winds increase tonight
into Monday, leading to periods of blowing snow, particularly at
DLH.

Precipitation at HYR and much of NW WI changes over to a
rain/snow mix Monday morning and then all rain Monday afternoon
and night. This mix isn`t expected to arrive at DLH until the
very end or shortly after the end of the current TAF period.
Ceilings remain low through Monday, through areas that switch to
a mix or all rain could see some improvement in visibilities.

&&

.MARINE...
Issued at 423 PM CDT Sun Mar 24 2024

A spring storm will bring gale-force winds to western Lake Superior
just as the commercial shipping season begins. The Gale Warning for
most of the nearshore zones of western Lake Superior has now been
extended to 1pm Tuesday.

East-northeasterly winds gradually increase today and tonight as an
area of low pressure develops in eastern Colorado then track east-
northeastward toward the Mid Mississippi RIver Valley on Monday. At
the same time, an increase area of high pressure in northern
Manitoba into far northern Ontario will result in an increasing
pressure gradient across Lake Superior and thus increasing easterly
winds. The strongest winds are expected Monday afternoon into Monday
night, turning from easterly to northeasterly through this
timeframe. Winds will be steady in the 25-30 knot range with gusts
of 35-40 knots, and while a few gusts as strong as 45 knots are
possible (10-20% chance in western Lake Superior), Storm-Force winds
are not likely (less than 5% chance). Waves may build to 10 to 15
feet across western Lake Superior on Monday, with the largest waves
on Monday evening. Winds turn more northerly on Tuesday as the low
pressure center approaches Lake Superior, moving across the lake
Tuesday night into Wednesday causing winds to turn northwesterly.

This storm will bring heavy snow and rain to Lake Superior, with
visibilities less than a half mile at times late tonight into
Monday, then around 3 to 5 mile visibility in an off and on wintry
mix Monday night through Tuesday.

West winds of 15 to 20 knots on Wednesday and Thursday as the area
of low pressure exits.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Winter Storm Warning until 7 PM CDT Tuesday for MNZ010>012-018-
     019-025-026-033>038.
     Blizzard Warning until 7 PM CDT Tuesday for MNZ020-021.
WI...Winter Storm Warning until 7 PM CDT Tuesday for WIZ001.
     Winter Storm Warning until 1 PM CDT Monday for WIZ002>004-
     006>009.
MARINE...Small Craft Advisory until 4 PM CDT Tuesday for LSZ121-148.
     Small Craft Advisory until 4 AM CDT Monday for LSZ140>145.
     Gale Warning from 4 AM Monday to 1 PM CDT Tuesday for
     LSZ140>145.
     Small Craft Advisory until 10 AM CDT Monday for LSZ146-147-150.
     Gale Warning from 10 AM Monday to 1 PM CDT Tuesday for LSZ146-
     147-150.

&&

$$

MESOSCALE...Rothstein
DISCUSSION...Unruh
AVIATION...Rothstein
MARINE...JJM


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