512
FXUS63 KDLH 272024
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
324 PM CDT Sat Apr 27 2024

.KEY MESSAGES...

- Another low pressure system will bring widespread rain Sunday
  through Monday. Very minor and localized accumulations of
  freezing rain may be possible along the higher terrain of the
  North Shore (20-40% chance).

- Strong northeast winds gusting up to 40-45 mph are expected
  Sunday afternoon through Monday morning along the North
  Shore. There is a low chance (20-30%) for lakeshore flooding
  along Lake Superior`s shorelines due to strong winds and high
  waves.

- Another rainy system is likely (60-70%) Tuesday into Tuesday
  night. There may be more rain later in the week.

&&

.DISCUSSION...
Issued at 324 PM CDT Sat Apr 27 2024

Rain continues this afternoon, mainly along and east of the
US-53 corridor. As low pressure continues moving northeast this
afternoon, the rain is expected to end along with it with
perhaps some lingering sprinkles into the evening.

An extended break between low pressure systems is expected tonight
and into Sunday morning. Models continue to slow down the arrival of
the next low pressure system on Sunday, bringing the next round of
rainfall in sometime around mid-day into the afternoon. As such, we
can expect lingering clouds tonight with mainly dry weather. Despite
there being plenty of low-level moisture, fog is not generally
expected as winds should remain strong enough to keep the lower-
atmosphere well mixed. The air aloft is expected to be dry enough
such that any breaks in the low-level clouds could bring some
brief patches of clearing.

As low pressure eventually moves northward on Sunday, a broad swath
of warm air advection-driven rain will overspread the region. The
previous system brought rainfall amounts anywhere from around a
quarter of an inch to an inch, and this was well within the forecast
amounts. For this second round, model ensembles continue to be in
pretty good agreement on rainfall amounts that will be similar,
albeit perhaps a touch higher than the first round. By and large,
amounts hovering around 1" are expected. Flooding threats will be
very minimal due to the long duration of the rain. Also, convection
potential will be minimal, similar to the last system. Model
soundings all suggest a deep inversion near the surface, so if there
are any bubbles of a few hundred J/kg of elevated CAPE that develop,
there could possibly be a few embedded rumbles of thunder, but this
is expected to be the exception rather than the rule. The rain
should persist into Monday, then gradually start to let up through
Monday afternoon and evening.

Now, for the folks who thought winter was over, we have some new
news for you! That`s right, a chance (albeit somewhat small;
~30-40%) for freezing rain for parts of the higher terrain along
the North Shore. The HREF and other ensembles have hinted at
just enough orographic cooling to result in temperatures falling
a degree or two below freezing Sunday night into early Monday
morning while rain falls to result in this freezing rain threat.
Now, a degree or two of temperature will make all the difference
in whether or not this happens at all. Models favor only the
higher terrain of the North Shore to see below or around
freezing temperatures, not directly along the shoreline.
Therefore, if any freezing rain does occur, it should be pretty
isolated. Areas from Two Harbors to Silver Bay and northeast
along the high terrain will be the target areas. NBM
probabilities for a glaze of ice approach 30-50% mainly around
the tip of the Arrowhead with probabilities diminishing further
southeast. Even where any freezing rain falls, accumulations are
likely to be quite minimal with temperatures starting out warm
and only falling to a degree or two below freezing for a ~6-8
hour period late Sunday night into early Monday morning. We will
continue to monitor this freezing rain potential, but right now
the risk for hazardous weather overall appears small.

Strong northeast winds are expected to accompany the rain Sunday
afternoon through Monday morning. There`s still a bit of spread in
ensembles for maximum wind gusts, but in general, the highest winds
and gusts can be expected along the North Shore of Lake Superior and
extending into the Twin Ports. Wind gusts around 40 mph are expected
frequently for areas within about 20 miles of the North Shore
shoreline, and NBM probabilities of gusts of 45 mph or higher vary
from 70-90%. As such, confidence is high enough with this forecast
update to issue a wind advisory along the North Shore. It`ll be
blustery out there, so hold on to your umbrellas tightly!

With these strong winds, we must also assess the possibility for
lakeshore flooding. From previous research, lakeshore flooding has
occurred in the Duluth area when the water level is at around 603`
(hovering between around 601.5` to 602.0` the past couple days).
Previous cases also featured sustained winds 22-30 kt, gusts 30-39
kt, and northeast flow duration around 24 hours or more. Wave
heights around 12-16 feet are usually a minimum for lakeshore
flooding. With this guidance in mind, the current forecast features
winds/gusts in that low-end threshold for a duration about 20-24
hours and wave heights in the 8-13 ft range (higher towards Silver
Bay, and closer to the lower end around the Twin Ports). With all
this in mind, confidence isn`t quite high enough to issue a
Lakeshore Flood Watch at this time. While some lakeshore flooding
can`t be ruled out, mainly around the Twin Ports, confidence is only
20-30% at this time. We will continue to monitor the potential for
lakeshore flooding in upcoming updates, and if confidence increases
to 50% or greater, we may toss out a watch so stay tuned for updates.

Another rain-making system is likely (60-70% chance) Tuesday into
Tuesday night. The originating track of this one will be from
Montana/Dakotas, and as such, it`ll have a bit less moisture to work
with. So, we`ll be looking at a 6-12 hour period of rain with
amounts more likely to hover around a quarter to half an inch.
Convective potential may be a smidge higher with this system,
however, with several models hinting at some instability stretching
up towards northwest Wisconsin Tuesday evening. It`s too early to
determine any potential hazards, but we`ll continue to monitor the
possibility for some thunderstorms with this Tuesday system.

Models become more divergent for the later part of the week, but
rain chances (20-40%) may continue in the later part of the
week with an amplified pattern aloft likely to persist.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1233 PM CDT Sat Apr 27 2024

MVFR ceilings are expected to be common through the period as
one low pressure system departs this afternoon and another one
arrives on Sunday. There is a slight possibility (20-30% chance)
that some VFR conditions could happen briefly tonight as there
may be some patches of clearing amongst the low clouds. In the
next 2-4 hours, visibility will be mostly VFR but occasionally
MVFR as showers continue to pass through. The general trend will
be for showers to end and visibility to improve as low pressure
departs. Visibility is expected to remain VFR tonight through
Sunday morning after rain moves away. Breezy conditions this
afternoon, but winds briefly become light tonight, switching
direction from northwesterly to northeasterly ahead of the next
low pressure system. Direction will be more variable this
afternoon at HYR closer to the low pressure center. Breezy
conditions redevelop Sunday morning along with rain chances
returning (30-50% chance) late Sunday morning from south to
north.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 324 PM CDT Sat Apr 27 2024

Winds will continue to weaken this evening as low pressure
departs. Waves up to 2-3 ft may still linger a bit into the
early evening before they weaken as well.

Attention then turns to another low pressure system that will
arrive mid-day to afternoon on Sunday, bringing rain and very
strong northeasterly winds. Winds will start to strengthen with
gusts to 25 kt late tonight, then gales are expected starting
Sunday morning around the Twin Ports, then extending elsewhere
Sunday afternoon. Winds will be strongest Sunday night into
Monday morning, then decreasing as the low pressure system
passes through Monday afternoon. This is expected to be a high-
end gale event with gusts to 40 to 45 knots, highest along the
North Shore Monday morning. In addition, wave heights around 8
to 14 ft are expected, especially along the North Shore and
Outer Apostle Islands. Breezy conditions and high wave heights
will persist into Monday night.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Wind Advisory from 4 PM Sunday to 4 PM CDT Monday for MNZ020-
     021.
     Wind Advisory from 4 PM Sunday to 10 AM CDT Monday for MNZ037.
WI...None.
MARINE...Small Craft Advisory from 4 AM Sunday to 4 PM CDT Monday for
     LSZ121-148.
     Small Craft Advisory until 4 PM CDT this afternoon for
     LSZ140>147-150.
     Small Craft Advisory from 4 AM to 4 PM CDT Sunday for
     LSZ140>143-146-147-150.
     Gale Warning from 4 PM Sunday to 4 PM CDT Monday for
     LSZ140>143-146-147-150.
     Small Craft Advisory from 4 AM to 10 AM CDT Sunday for LSZ144-
     145.
     Gale Warning from 10 AM Sunday to 10 AM CDT Monday for LSZ144-
     145.

&&

$$

DISCUSSION...JDS
AVIATION...JDS
MARINE...JDS