962
FXUS63 KDLH 162147
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
447 PM CDT Sun Jun 16 2024

.KEY MESSAGES...

- Scattered storms this afternoon into evening. Some of these
  storms could become severe (15-20% chance) with 1-2" hail
  being the main threat during the afternoon, but transitioning
  to damaging winds during the evening. There is also a low-end
  threat for a tornado (<5%).

- Very heavy rain and potential for flash flooding (50-70%
  chance), potentially localized considerable flash flooding,
  especially from central MN into the Iron Range and south into
  portions of NW WI Monday and Tuesday where a Flash Flood Watch
  has been issued. Scattered strong to severe storms are
  possible as well (15% chance) again Monday PM into Monday
  night and again on Tuesday.

- Rain and storm chances return late this week into next
  weekend.

&&

.DISCUSSION...
Issued at 444 PM CDT Sun Jun 16 2024

Rest of today - this Evening:

A few thunderstorms have begun initiating across Koochiching and
northern St. Louis counties ahead of the cold front. So far
these storms have remained sub-severe for the most part, though
a few have been a little stronger with the potential to produce
hail to the size of pennies around quarters in one or two of
them. The environment along and ahead of the cold front remains
highly unstable, with MUCAPE now having reached 1500-3000 J/kg
across much of the Northland, highest with southward extent as a
result of steep mid-level lapse rates (7-7.5 C/km). Low-level
lapse rates have been a bit poorer, so the main threat through
the remainder of the afternoon is primarily large hail (up to
1-2" in diameter), though some localized wind gusts to 60 mph
cannot be ruled out as storms become surface based as the
capping inversion erodes. O-6km bulk shear of 40-50 knots will
continue to favor initial development being initially discrete
cells given mostly straight hodographs with initial storm motion
to the east to northeast. Short term guidance does suggest
storm development along the cold front to occur in central MN,
as well, due to the cap eroding there, too. As we push into the
evening, storms will gradually propagate east along and just
ahead of the cold front, potentially growing upscale into a
broken line or cluster of storms. This transition in storm mode
would also transition the primary severe hazard threat being
more in the form of damaging winds to 60 mph, with a large hail
threat (1") as storms track into the Arrowhead, Twin Ports, and
NW WI. Still can`t rule out a low-end tornado threat (<5%
chance) this evening given there will be some slight turning in
the low levels that could give these storms access to around 100
m2/s2 of effective SRH, with the best environment in the Twin
Ports to NW WI. Severe storm potential should wane and exit to
the east/southeast of the area by late evening, mainly around
10pm- midnight. Some locally heavy rainfall (quick 0.5-1") will
be possible with any storm, though the localized basis should
preclude minor flooding potential.

Persistent cloud cover much of the day has also limited the high
temperatures that were forecast, with most locations peaking in
the 70s, though parts of east-central MN into western Wisconsin
have touched the low 80s with dewpoints around 70 degrees. This
has led to heat index values peaking mainly less than 90
degrees.

Monday - Tuesday Heavy Rain/Flooding Threat:

There will be a brief break in rain during the first half of the
overnight hours tonight, but then another push of strong
moisture advection along with a passing weak upper-level
shortwave will favor the return of widespread rain/non-severe
storms moving in from our south early Monday morning and
persisting into mid-late Monday morning along and north of the
stationary surface front setting up across central Minnesota
into NW WI. A second round of developing showers/storms Monday
afternoon pushes northward and sets up in northern and
northeastern MN Monday evening into Monday night along and
north of a northward moving warm front (formerly the stationary
front). This later Monday round is when the heaviest rain and
flash flooding threat will be maximized as PWATs reach above
1.8-2" (near maximum of climatology), though an additional round
of showers and storms are likely to develop along and ahead of a
cold front Tuesday PM leading to lingering flash flooding
potential on Tuesday/Tuesday night if storms track over the same
locations with these several rounds. With that said, there is
still a bit of uncertainty in CAM guidance on where the
heaviest rain will fall through Tuesday evening depending on
how quickly the stationary front/warm front moves northward on
Monday. We will be looking at 1-3" of rainfall across the
Northland, with localized amounts of 3"+ (15-30% chance) from
the Brainerd Lakes to the Iron Range and areas southeast,
generally in line with locations where a Flash Flood Watch has
been issued. The Flash Flood Watch is in effect from 1 PM Monday
to 7 AM Wednesday to capture the several rounds of heaviest
rainfall and lingering flooding concerns. Shifts to the coverage
and locations of heaviest rainfall and locations are still
likely, so changes to the Flash Flood Watch coverage and
duration are likely to change.

Monday - Tuesday Severe Potential:

For later Monday into Monday night, there is an additional
threat for scattered severe storms along and north of the
northward pushing warm front. These storms will be predominately
elevated in nature, so the main risk will be large hail, but
there will also be a lower end threat for damaging wind (5%
chance) and perhaps a tornado (2% chance) for storms nearest to
the warm front.

Tuesday will also see a potential for severe storms (15% chance),
primarily along an eastward pushing cold front on Tuesday
afternoon and evening as the surface low pushes northeast of the
Northland. The CAPE/shear combination--with shear being parallel
to the cold front--would support more of quick upscale growth
into a line of storms, so the main threat would be in the form
of damaging wind gusts, with a lesser threat of hail up to the
size of quarters. The severe threat diminishes with eastward
extent into north-central WI later Tuesday evening with the loss
of daytime heating.

Mid-Week Lull:

There will be a brief break in precipitation by mid-week
(Wednesday-Wednesday night) as surface high pressure moves
through the region.

Additional Late Week/Weekend Active Weather:

Looking ahead into late this week into next weekend, models
point to another active pattern of showers and storms with some
heavy rain and severe potential yet again, though confidence at
this timeframe is lower due to varying model solutions regarding
the timing of shortwave troughs and surface lows.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 116 PM CDT Sun Jun 16 2024

Stubborn onshore flow off of Lake Superior has led to periodic
intrusions of dense fog into KDLH and North Shore terminals along
with LIFR to VLIFR ceilings. Expect these low ceilings and fog
to hang around into mid afternoon until winds can take on a more
southerly direction. IFR ceilings at KHIB should also rise to
MVFR by mid-afternoon. Otherwise, the remainder of the area is
sitting under MVFR ceilings. Confidence has increased in the
development of scattered showers and thunderstorms along a cold
front in north-central Minnesota later this afternoon initially
as individual storms, and then potentially growing into a line
of storms this evening as storms and the front push southeast.
Still need to pinpoint the exact timing of storms to terminals
downstream, so amendments are likely later this afternoon and
evening. There is a 15% chance that some of these storms could
be strong to severe, containing very large hail (2"+ in
diameter initially during the afternoon in NE MN). Damaging
winds are also possible, but would become the primary threat this
evening as storms transition into a line. Ceilings are expected
to lift to VFR this evening. Some MVFR to locally IFR visibilities
likely with the storms. There will be a brief break in
precipitation tonight before another round of showers and storms
move in from the southwest later tonight into Monday morning.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 444 PM CDT Sun Jun 16 2024

Dense fog continues to persist along the Twin Ports and North
Shore, so have extended the Marine Dense Fog Advisory through
this evening due to the weather pattern not really changing
until storms move over the Lake this evening. Scattered storms,
with a 15% chance of becoming strong to severe may push east
into western Lake Superior this evening. Still expect the strong
to severe storm threat to end around mid-evening as storms push
southeast and weaken, so the window of time for severe potential
is short (roughly 3-4 hours). Large hail and gusty, erratic
winds will be the main threats with the storms. Expect onshore
flow for most places the rest of today, with a shift to
southwesterly overnight, then back to onshore flow out of the
east to northeast on Monday. Winds may gust to around 15 kt
today, decreasing tonight, and then gust to around 15 knots
again on Monday.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch from Monday afternoon through Wednesday morning
     for MNZ019-025-026-033>038.
WI...Flood Watch from Monday afternoon through Wednesday morning
     for WIZ001-006-007.
MARINE...Dense Fog Advisory until 1 AM CDT Monday for LSZ140>145.

&&

$$

DISCUSSION...Rothstein
AVIATION...Rothstein
MARINE...Rothstein