867
FXUS63 KDLH 170607
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
107 AM CDT Mon Jun 17 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 /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 107 AM CDT Mon Jun 17 2024

VFR conditions are expected to prevail early this morning ahead
of showers lifting in from the southwest closer to daybreak.
Showers are expected to increase in coverage through the day
along with intensity leading to MVFR visibilities. Some
thunderstorms will be possible during the afternoon and early
evening hours before showers take back over with MVFR
visibilities and ceilings. Light winds tonight will become
easterly Monday as a boundary stalls out across the region.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 938 PM CDT Sun Jun 16 2024

Dense fog will persist from the Twin Ports to the North Shore
through late evening or early morning. We`ve extended the Dense
Fog Advisory through 5 AM CDT from Taconite Harbor to Grand
Portage. Fog will also be possible along the South Shore but
it`s not expected to be as widespread. A few thunderstorms will
be possible tonight, mainly along the South Shore. An isolated
severe storm is possible capable of producing hail and gusty and
erratic winds in excess of 40 knots. Winds will switch to west
to southwest overnight, then back to onshore flow out of the
east to northeast on Monday. Winds will gust to around 15 knots
again on Monday and increase a bit into Monday night. More
thunderstorms are expected Monday into Tuesday.

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 this afternoon through Wednesday morning for
     MNZ019-025-026-033>038.
WI...Flood Watch from this afternoon through Wednesday morning for
     WIZ001-006-007.
MARINE...Dense Fog Advisory until 5 AM CDT early this morning for
     LSZ140-141.

&&

$$

DISCUSSION...Rothstein
AVIATION...BJH
MARINE...Melde