315
FXUS63 KDLH 071117
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
617 AM CDT Tue May 7 2024

.KEY MESSAGES...

- A band of moderate rain moves into the Northland early this
  morning and spreads from southwest to northeast through this
  afternoon. Rain showers persist into tonight, especially in
  northeast Minnesota.

- Scattered strong thunderstorms may (30% chance) form this
  afternoon mainly south of US Highway 2 and produce small hail
  and wind gusts to 40 mph. There remains a 5% chance of an
  isolated severe thunderstorm capable of producing around
  quarter size hail over inland northwest Wisconsin early this
  evening.

- Fog late Tuesday night may be locally dense near Lake
  Superior.

- Frost headlines for this warm season begin to be issued as of
  today. Frost is possible (40% chance) in the Arrowhead
  Wednesday night. Freezing conditions in northwest Wisconsin
  and widespread frost into the I-35 corridor and Arrowhead are
  possible (60% chance) Thursday night.

- Two weak Canadian shortwave troughs passing over the area may
  (20-40% chance) bring additional light rain both Friday PM
  and Sunday.

&&

.DISCUSSION...
Issued at 348 AM CDT Tue May 7 2024

Vertically stacked low pressure centered over West River South
Dakota is draping an occluded front over the Midwest early this
morning. A band of rain and scattered thunderstorms persists
along the occluded front in west-central Minnesota, but moving
slowly north-northeastward. The first locally heavy rain showers
have already formed in the Brainerd Lakes region over the last
half-hour, with coverage expected to expand into east-central
Minnesota and the western Iron Range. Precipitable water values
of 1.1-1.2" shortly-incoming within this front-parallel flow
pattern aid in very localized heavy rainfall and pea size hail
being the expected primary hazards with this first round of rain
showers. Short-term mesoanalysis shows increasing mid-level
lapse rates in an area of 100-150 J/kg of MUCAPE supporting the
20% chance in the forecast for an isolated thunderstorm as well
in this southwestern part of the Northland this morning.

As the low pressure retrogrades westward into the Northern High
Plains, better mid and low-level fgen forcing aids in a band of
moderate rainfall forming from 5 AM to 8 AM, while lifting
northeastward into the Iron Range, northwest Wisconsin and the
Arrowhead as well. Anywhere from a few tenths to three-quarters
of an inch of rainfall is expected this morning and into mid-day
for areas along and south of the Iron Range in Minnesota and
across all of northwest Wisconsin, except parts of northern Iron
and Ashland Counties.

After the main frontal band of rainfall exits the southern half
of the Northland towards early afternoon, the better chances of
scattered strong thunderstorms build into the region mainly
along and south of US Hwy 2. An initial round of scattered
strong thunderstorms is progged to again form in the Brainerd
Lakes region between 1-3 PM today within an environment of
minimal mid-level lapse rates (6 C/km) and CAPE (~100 J/kg).
The minimal organized shear supports more of a pulse strong
thunderstorm environment with collapsing updrafts fairly quickly
to create downburst winds around 40-45 mph and maybe small hail
around 1/2 inch in size.

High-res, short-term models are in fair agreement on showing
this storm environment quickly moving eastward into the east-
central MN and inland northwest Wisconsin by early this
evening. Slightly better mid-level lapse rates (6.5-7 C/km) and
slightly more organized shear around 25 knots within a CAPE
profile around 150 to maybe 200 J/kg is expected to help support
the best potential (30% chance) for the strongest storms later
today in inland northwest Wisconsin and maybe Pine County in MN
from about 4-9 PM this evening. At this point, wind gusts to 45
mph and hail the size of nickels or smaller is expected in
nearly all storms that may form. There is an outside (5-10%
chance) potential of an isolated severe storm though just making
it into southern parts of Washburn, Burnett, Sawyer and Price
Counties later today. The primary threat would be large hail
about an inch in diameter, but again only around 5-10% chance
for any severe storm threat for this very limited coverage area.

After the storm potential in inland parts of the Northland later
this evening, rain showers and drizzle remain likely (60%
chance) for the Arrowhead and Twin Ports through the overnight
hours. Model forecast soundings show signals for overnight fog,
most dense near Lake Superior, so areas of fog is mentioned in
the forecast into early Wednesday morning.

Easterly flow continues to create overcast skies for much of the
region into Wednesday, but clearing in the Borderlands and near
and south of US Hwy 8 is expected into the afternoon hours
tomorrow while the isolated rain showers persist elsewhere.

Due to vegetation becoming more susceptible to freezing
temperatures and frost formation (per guidance from the Midwest
Regional Climate Center) and the climatological trends for
freezing temperatures ending from south to north this time of
year in the Northland, NWS Duluth will begin the routine
seasonal issuance of frost/freeze headlines again beginning
today. With that said, the first potential for a frost headline
may be Wednesday night in the Arrowhead as temperatures are
forecast to get down to the 33-34 F (40% chance) at the surface
to support frost formation. Although, even better and more
widespread potential (60% chance) exists Thursday night for
freezing temperatures in northwest Wisconsin and frost in the
I-35 corridor and across the Arrowhead. Any headline potential
will be further assessed on Wednesday, but this is an early
heads up for those that have outside plants already or early
starts to the garden! One item to watch for Wednesday night will
be just how tight the remaining pressure gradient allows the
near-surface winds to decrease to allow for optimal frost
formation.

An incoming shortwave trough from Canada Friday morning is
expected to create at least some light rain showers, potentially
localized moderate rainfall of another couple of tenths) that
afternoon and evening. A similar setup on Sunday then looks to
be another shot at widely scattered rain showers as well to end
the weekend. Negating the easterly winds keeping stout lake
breezes in play for within 50 miles of Lake Superior today
through Thursday and temperatures in the 50s, inland locations
will see high temperatures in the 60s for this forecast period.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 612 AM CDT Tue May 7 2024

An approaching front will increase rainfall at area terminals
from 16Z this morning through the afternoon, bringing MVFR
skies and visibility, locally down to IFR. The heaviest band of
moderate rain is expected to have a residual period of 3-4 hours
today at each terminal before more localized rain showers
setup, especially for northeast Minnesota. Incoming instability
this afternoon produces a 20-30% chance of isolated strong
thunderstorms from BRD (18-21Z) to RZN (20-02Z to HYR (22-03Z).
Vicinity thunderstorms was kept at HYR for uncertainty by a
couple of hours on best thunderstorm chances, but there has been
an increase in confidence for BRD so a TEMPO is in place. Fog
is expected tonight, mainly after 03Z and lasting into early
Wednesday morning, and likely (50-60% chance) to produce at
least IFR visibility for terminals near Lake Superior.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 612 AM CDT Tue May 7 2024

A constricted pressure gradient keeps elevated and gusty east to
northeast winds late tonight, but further strengthening towards
sunrise and mid-morning. The gustiest winds, near-gale force,
are possible (40% chance) from Two Harbors to Grand Marais for a
few hour period. Kept with only Small Craft Advisories for the
short-duration and more stable regime keeping the strongest
winds likely (60% chance) from reaching the surface waters
today. Expect already elevated wave heights by early morning to
further build into the mid-day period today and remain with
elevated swell through tonight. There is a 20% chance of
isolated thunderstorms from the Twin Ports to the South Shore
this evening. Areas of marine fog are expected into early
Wednesday morning (with a 30% chance of visibility less than 1
nautical mile). Gusty northeast winds persist, although slower
in speed compared to today, on Wednesday with Small Crafts
remaining in effect.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
MARINE...Small Craft Advisory until 4 AM CDT Wednesday for LSZ140-147-
     150.
     Small Craft Advisory until 4 AM CDT Wednesday for LSZ141>146.
     Small Craft Advisory from 10 AM this morning to 4 PM CDT this
     afternoon for LSZ148.

&&

$$

DISCUSSION...NLy
AVIATION...NLy
MARINE...NLy