187
FXUS63 KDLH 152106
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
406 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Showers and thunderstorms this afternoon into tonight. Severe weather
  is not expected, but heavy rainfall could cause localized
  minor flooding in northwest Wisconsin tonight (~25% chance).

- Isolated strong to severe thunderstorms are possible late
  Sunday afternoon and evening (~5% chance), with large to very
  large hail and strong winds as the main threats.

- The threat for very heavy rain and flash flooding is
  increasing Monday through Tuesday (40-60% chance). Strong to
  severe storms capable of producing large hail and locally
  damaging wind gusts are also possible (15% chance) Monday
  afternoon into Monday night, with a 15% chance for severe
  weather again on Tuesday.

&&

.DISCUSSION...
Issued at 405 PM CDT Sat Jun 15 2024

Rest of today - Tonight:

Warm air and moisture will continue surging in from our south
the rest of this afternoon into tonight, bringing an area of an
area of PWATs up to 1.6-1.8" (95th+ percentile of climatology)
into east-central Minnesota into northeast Wisconsin. This
anomalous moisture combined with energy from a shortwave trough
passing through the Northland, will support a broad area of
showers and embedded thunderstorms. The focus of highest
rainfall with this band of precipitation will be in the
aforementioned area where PWATs will be highest, particularly in
NW WI. The HREF 24-hour localized PMM rainfall forecast paints
some pockets of 1-1.5" of rainfall in Sawyer and Price counties
through Sunday morning, while amounts drop off to ~0.75-1" for
the remainder of NW WI, and generally 0.5" or less for areas in
northeast Minnesota. This first round of rainfall will be
relatively quick moving, so the chance for localized minor
flooding is lower (25%) chance where the heaviest rain falls in
NW WI due to already saturated soils and elevated streamflows
from previous rainfall. A few short-lived, strong storms with
small hail cannot be ruled out with the overnight into early
Sunday morning convection in NW WI either given MUCAPE around
200-700 J/kg and about 20-25 knots of 0-6km bulk shear.

Sunday:

Precipitation diminishes/shifts east by early to mid Sunday
morning, leading to a break in rainfall for a good part of the
day as a very subtle shortwave ridge moves overhead.
Substantial low-level warm air advection continues into Sunday
leading to the potential development of 2000-3500 J/kg of
MUCAPE by the afternoon hours, but will also result in the
development of a strong capping inversion. Short-range guidance
still varies a bit on how strong the capping inversion will be
during the day, and depending on the rate of surface heating,
could potentially be eroded in north-central Minnesota by mid-
afternoon along a weak cold front where at least some weak
forcing for upward ascent would be present. If the capping
inversion were to erode, the large amount of instability
combined with 0-6km bulk shear magnitudes of 40-50 knots would
be supportive of conditional severe weather potential (5%
chance). Large to very large hail (2"+) would be the initial
threat with these storms if they do develop due to the
shear/CAPE combination support supercell storm structures, with
a transition to some clusters during the evening into the
Brainerd Lakes to NE MN where the severe threat would be more in
the form of large hail and locally damaging wind gusts. These
storms would then push east of the Northland/diminish by the
early overnight hours. Can`t rule out some locally heavy
rainfall with these storms, as well.

The other concern for Sunday will be abnormally hot temperatures.
Highs in the upper 80s are expected in east-central Minnesota
and northwest Wisconsin, which, when combined with low to
mid-70s dewpoints, will produce heat index values in the low to
mid-90s. While not quite to Heat Advisory thresholds, those who
are sensitive to heat, especially without effective cooling or
adequate hydration, will be most at risk for being affected by
these very muggy conditions. Elsewhere in the Northland, expect
low to mid-80s for highs with heat index values in the 80s.

Late Sunday Night - early Monday:

Another round of rainfall makes its way into the Northland late
Sunday night into Monday morning as a strong low-level jet
develops in association with another shortwave trough passing
through the Northland. This initial overnight/morning convection
would be elevated in nature just to the north of a west-east
oriented stationary front across central MN into western/NW WI,
but be capable of producing at least some large hail, with
perhaps a few localized gustier winds making it to the ground
level. Heavy rainfall and flash flooding also becomes a concern
with this round of convection as storm motion looks to be
generally west-east along the front, with the potential for
storms repeatedly moving over the same locations with
anomalously high PWATs to 1.6-1.9" once again. Depending on
where exactly the stationary front and associated convection set
up will dictate where this heaviest rain will fall as short-
range guidance still varies a bit on how far north the
convection sets up, some in southern parts of the Northland, and
others even farther south across southern MN and western WI. It
is

Late Monday - Tuesday:

Additional elevated instability develops north of the surface
front that will now be migrating slowly northward again for
later Monday into Monday night ahead of an ejecting surface low
coming off the lee of the Rockies. This would lead to another
threat for scattered severe storms, with large hail as the
primary threat, but also some damaging wind potential for storms
closest to the front.

Into Tuesday, a cold front is likely to pass through on the back
side of this system as the surface low ejects northeast, with
the combination of CAPE/shear/moisture along the front conducive
for severe storms, with damaging winds more so as the main
severe threat as these storms form more of a line when passing
through from west to east.

Perhaps the biggest concern for Monday through Tuesday will be
the heavy rain and flash flooding given repeated rounds of
thunderstorms falling on already wet soils. A deep, saturated
layer below the freezing level combined with PWATs likely around
2" or slightly more (near maximum of climatology) would produce
very efficient rain processes and higher rainfall rates.
Ensemble guidance even points to 24-hour accumulations of 2-3"
from Monday evening through Tuesday evening, with even up to 4"+
in the Brainerd Lakes region (15-30% chance). This all said, it
is becoming increasingly likely (40-60% chance) that flash
flooding could occur Monday into Tuesday, so a Flood Watch
issuance may be necessary as we get closer to that timeframe.
This agrees well with the issuance of a Moderate WPC Excessive
Rainfall Outlook (ERO) for Monday-Tuesday. For context, the
last time we have had this high of an ERO risk was back on
August 14th, 2020 when Brainerd to Grand Rapids had some
flooding and several inches of heavy rainfall.

There looks to be a brief break in precipitation by mid-week
(Wednesday) as surface high pressure moves through, but another
active and wet pattern could rear its head again heading into
later this coming week into next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1245 PM CDT Sat Jun 15 2024

A few isolated showers are moving out of far northern Minnesota
early this afternoon, with conditions remaining VFR for at
least a few hours. However, another round of rain will move into
the region from the south by mid-afternoon, primarily affecting
KBRD/KDLH through this evening/early overnight and lingering at
KHYR from this afternoon into early Sunday morning.

Ceilings gradually fall into MVFR for most sites this evening,
then IFR to LIFR overnight into Sunday morning, with a 20%
chance for DLH to even hit VLIFR ceilings. Sites with rain will
also see MVFR to locally IFR visibilities develop with and
immediately behind the rain. Some embedded thunderstorms are
possible near KBRD and particularly KHYR this evening and
overnight.

Southerly winds increase today with gusts to around 20 knots
into this evening, though weaken slightly overnight for all but
KHYR.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 405 PM CDT Sat Jun 15 2024

Easterly winds will be less than 20 knots tonight into Sunday
morning, but the longer fetch will briefly produce 2-4 ft wave
heights from Taconite Harbor to Grand Portage early to mid
Sunday morning. There will be a chance for thunderstorms
tonight into Sunday, with the highest potential (30%) from the
Twin Ports along the South Shore.

Easterly winds on Sunday of around 10 to 15 knots turn light and
southerly Sunday night and then northeasterly at 10 to 15 knots
on Monday. Look for stronger south to southwest winds on
Tuesday, with daytime gusts up to 25 knots to possibly produce
hazardous conditions for small craft. Scattered strong to severe storms
capable of producing large hail or strong winds are possible
Sunday late afternoon and evening (~5% chance). Daily
thunderstorm chances continue on Monday and Tuesday, with large
hail and gusty winds as the main threats.

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 from 6 AM to 10 AM CDT Sunday for LSZ140-
     141.

&&

$$

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