Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 241715
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1215 PM CDT Sun Mar 24 2024

.KEY MESSAGES...

- Messy winter storm moves into the area through the day Sunday.
  Heavy wet snow, high winds, mixed precipitation, and ice all
  expected. Blizzard conditions likely along the North Shore.

- Snow amounts have trended lower by an inch or two with this
  forecast. Ice accumulations of up to a tenth of an inch are
  possible over portions of northwest Wisconsin tonight and
  early Monday morning. Ice accumulations of up to two tenths of
  an inch are possible Monday night and early Tuesday morning
  over portions of the North Shore into the Twin Ports.

- Heavier precipitation wraps up through Tuesday with some light
  scattered snow showers possibly lingering into Thursday.

- Temperatures warm slightly into the weekend along with our
  next chance for precipitation.

&&

.MESOSCALE...
Issued at 1206 PM CDT Sun Mar 24 2024

An area of deep saturation around -15C aloft has resulted in
some efficient dendritic snow growth this morning associated
with warm air and moisture advection and some weak and
disorganized mid-level frontogenesis. With that, we’ve observed
some fluffy snowfall accumulations around half an inch to an
inch and a half around the Twin Ports and locally higher amounts
to 3” around Brainerd. This deeper area of dendritic saturation
is moving north, and is expected to continue doing so going
through the early afternoon. To the south of that, roughly from
Ashland to the Twin Ports to Aitkin, a much smaller dendritic
growth layer has allowed for snowfall rates to remain very
light. Better synoptic forcing to the south is resulting in more
light to moderate snowfall rates as indicated by visibilities
down to around 1-2 miles from Brainerd to Hinckley to Spooner.

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 currently 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. 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. Thus, additional
accumulations around 2-3” with locally higher totals are
expected through around sunset for most locations roughly south
of US 2. With southeast winds expected to become more
northeasterly through the afternoon, orographically-enhanced
snow along the North Shore is expected to continue, so despite
the broader synoptically-forced snow remaining more in northwest
Wisconsin, snowfall rates and accumulations around the higher
terrain of the Twin Ports and up the North Shore are expected to
be around the 2-3” mark (locally higher), similar to areas
further south.

&&

.DISCUSSION...
Issued at 502 AM CDT Sun Mar 24 2024

Forecast remains generally on track with a messy long-duration
wintry storm system impacting the region for the next several
days. Main updates with this forecast include slightly lower
snow totals and slightly higher ice accumulation for some
locations. Maximum wind gusts have also trended lower along the
North Shore as warm air advection aloft will limit mixing into
the stronger winds in the low-level jet.

Split upper-level flow over North America was indicated by
GOES-East water vapor imagery and RAP analysis as of 09Z. A
northern stream jet max was located over southern Manitoba and
northern Ontario while a stronger and larger southern stream jet
max was positioned over the Baja nosing into southern New
Mexico and western Texas. There may be limited phasing between
these features while cyclogenesis is favored in the exit region
of the southern stream jet. A weak area of surface low pressure
was beginning to take shape over eastern Colorado and northern
New Mexico. A modest zone of 850-700 mb frontogenesis stretched
from western North Dakota east-southeastward into northern
Wisconsin which was supporting a band of light snow from central
North Dakota into northwest Wisconsin. Warm air advection and
isentropic ascent supported a larger area of light snow over
southeast Minnesota and southwest Wisconsin.

This initial band of snow will weaken over the next several
hours while the warm advection snow propagates eastward out of
the region. This lull in snowfall will persist for several hours
before the next surge of moisture and forcing for ascent
develops later this morning. By 18Z the surface low will
coalesce over southeastern Colorado and large scale forcing for
ascent will increase over the Upper Midwest. Light snow will
spread northward from South Dakota and Nebraska into southern
and central Minnesota by about 18Z.

There will be several surges of moisture working northward over
the next 36 hours. Look for snow to intensify and spread north,
then weaken and shunt eastward, then redevelop as repeated
waves of moisture and forcing ripple through the region. Overall
we have slowed the northward progression of precipitation today
with this forecast. Convection over the southern Plains and
lower Mississippi River Valley will push the poleward moisture
transport farther to the east than earlier forecasts. Forecast
thermal profiles suggest a thin -12 to -18 C dendritic growth
layer which is well aloft (650-500 mb). The strongest layer
forcing will be found below that level in the warmer portion of
the profile. Therefore we have lowered snow ratios with this
forecast. Look for rimed dendrites and graupel to be common
snow crystal habits. Precipitation amounts trended slightly
higher, however, which resulted in only a slight decrease in
forecast snow amounts of an inch or two.

A strong southerly low-level jet will pump a melting layer well
northward tonight through early Tuesday morning. Precipitation
will likely change over to rain from south to north over
northwest Wisconsin, possibly as far north as the Arrowhead by
12Z Monday. There is a brief possibility of freezing rain as the
surface temperatures lag behind the warm air advection aloft.
As a result portions of Sawyer, Price, Ashland, and Iron
counties could see up to a tenth of an inch of ice accumulation
from around midnight tonight through mid-morning Monday. The
long time window is more a function of timing uncertainty rather
than actual duration. Freezing rain should be limited to an
hour or two before surface temps climb above freezing. That
trend will repeat along the North Shore down into the Lake Mille
Lacs area Monday evening into Tuesday morning. Freezing rain
amounts are a little higher during that timeframe due to
reinforcing cold air advection southeastward from Ontario in
competition with the warmer air aloft.

The strong surge of warm air aloft will limited the wind gust
potential over northeast Minnesota. The shallow inversion will
prevent mixing into the strongest core of the low-level jet. We
still think there is a period of time when blizzard conditions
will develop over the North Shore, perhaps a little later Monday
morning than previous forecasts, starting as late as 12Z Monday
and persisting into Monday evening when the snow changes over
to rain.

A few rumbles of thunder are not out of the question in the
warm sector Monday afternoon through Tuesday morning. There may
even be a period of thundersnow over portions of the North
Shore.

The system will continue to tighten up and lift north-
northeastward through Wisconsin and into northeast Ontario on
Tuesday and Tuesday night. Precipitation should stay rain over
northwest Wisconsin until late Tuesday afternoon or Tuesday
evening before changing back to snow. For details regarding snow
and ice accumulation, please see weather.gov/duluth/winter and
weather.gov/media/dlh/DssPacket.pdf.

Snow showers and flurries may linger off and on through
Thursday and temperatures will remain below normal. Another shot
of wintry weather is possible next weekend, although confidence
has decreased since yesterday.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1215 PM CDT Sun Mar 24 2024

MVFR to IFR conditions today as heavy snowfall begins to develop
across most TAF sites, becoming LIFR to VLIFR for a period late
tonight through Monday morning. Following a morning round of light
snow, there will be a break in the snowfall this afternoon before
the main round of heavy snowfall moves in from south to north.
Ceilings will quickly fall to IFR levels around 800-1000 ft AGL with
visibilities down to a mile or less this evening. Overnight heavy
snowfall rates will lead to half mile or less visibility at times.
Increasing winds on Monday will cause periods of blowing snow,
especially at DLH.

Beyond the TAF period, precipitation changes over to a mix of rain
and snow at HYR and eventually DLH on Monday, which may improve
visibility, but ceilings will remain IFR or worse through the
day.

&&

.MARINE...
Issued at 403 AM CDT Sun Mar 24 2024

A large winter storm will cross over Lake Superior through the
next 48 hours bringing gale force northeast wind gusts tonight
into Monday. Waves will build to over 10 feet Monday night
before decreasing slowly Tuesday. Waves and winds will remain
above small craft advisory criteria through much of the week.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Winter Storm Warning until 7 PM CDT Tuesday for MNZ010>012-018-
     019-026.
     Blizzard Warning until 7 PM CDT Tuesday for MNZ020-021.
     Winter Storm Warning until 7 PM CDT Tuesday for MNZ025-033>038.
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 1 AM CDT Monday for LSZ140>145.
     Gale Warning from 1 AM to 10 PM CDT Monday for LSZ140>145.
     Small Craft Advisory until 10 AM CDT Monday for LSZ146-147-150.
     Gale Warning from 10 AM to 10 PM CDT Monday for LSZ146-147-150.

&&

$$

MESOSCALE...JDS
DISCUSSION...Huyck
AVIATION...JJM
MARINE...Wolfe


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