854
FXUS63 KDLH 180001
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
701 PM CDT Mon Jun 17 2024

.KEY MESSAGES...

- Flash Flood Watch area remains unchanged with this update,
  though the there are still some pockets of 1.5-3" of rainfall
  possible with storms this evening into tonight and again on
  Tuesday. Highest amounts are expected along and north of the
  Iron Range.

- Main severe threat for this evening into early tonight with
  elevated storms will be hail (5-10%). Can`t rule out some
  gusty winds for storms closer to the surface warm front.

- Additional potential for a line of strong to severe storms
  (15%) on Tuesday as it works across the region. Main risk will
  be damaging wind gusts to 60, though some large hail and a
  low-end threat (2%) for an embedded tornado are also possible.

- Additional chances for rain and storms this weekend, with
  heavy rainfall potential, as well.

&&

.DISCUSSION...
Issued at 439 PM CDT Mon Jun 17 2024

Rest of Today:

The Northland is experiencing a brief period of rain-free
weather this afternoon as showers/storms across southern MN into
western WI are occurring north of the surface warm front draped
across northern Iowa into central WI. There has even been some
clearing between some high clouds for northern MN this afternoon
with high temperatures in the 70s there, but 60s form east-
central MN to the Twin Ports and NW WI where the cloud cover has
hung on.

This Evening - Tonight:

Showers and thunderstorms make a push back into the Northland
from our south starting mid-late this evening as the warm front
surges northward, and persist into the overnight hours along and
north of the front. CAMs are still in disagreement on the
the coverage and eastward extent of these storms later this
evening into tonight, but do favor the best coverage over
north-central Minnesota where the better forcing for ascent
will be present ahead of the approaching low pressure center.
Rich moisture advection (PWATs of 1.6-1.9", near maximum of
climatology for mid-June) and marginal mid-level lapse rates
(6-7 degC/km) will aid in the production of 700-1500 J/kg of
MUCAPE this evening into tonight. The CAPE/Shear combination
would support a marginal threat for severe hail (5-10%) in the
elevated storms over north-central MN. Can`t rule out some
stronger wind gusts up to 50-60 mph for storms closer to the
surface warm front, but the elevated nature of most storms
should keep the wind threat lower (5% chance). The severe threat
weakens the later we get into the overnight hours.

As for rainfall, QPF amounts have continued to trend slightly
downwards for this evening and tonight. Amounts generally range
from 0.25-0.5" in NW WI to 0.5-1.25" in the Minnesota side of
our forecast area, with the highest amounts in north-central MN
where storm coverage will be better. The Flash Flood Watch
remains in place as is due to some signal for localized pockets
to 1.5" tonight and additional rainfall with Tuesday`s storms
(more details below). These amounts aren`t too entirely high,
but will likely be coming in a relatively short timeframe onto
already saturated soils and in efficient rainfall rates in the
storms due to high PWATs and a deep warm/moist layer in the
atmosphere. Can`t rule out some ponding or minor flooding due to
the rainfall, but are no longer expecting considerable flooding
potential.

Tuesday - Tuesday Evening:

A strong Colorado low ejecting northeast into the eastern
Dakotas by Tuesday morning will keep showers/storms lingering
over north-central Minnesota through much of Tuesday morning as
the warm front lifts towards the International Border, while the
rest of the Northland could see some lingering drizzle or
spotty showers given lingering low-level moisture and cloud
cover. This sets the stage for how the rest of Tuesday will
turn out with regards to storm development along/ahead of the
cold front Tuesday afternoon and evening as it could affect
whether afternoon high temperatures can become warm enough to
overcome the weaker capping inversion, particularly for north-
central MN where morning convective will linger longest. With
that said, most of the Northland will still see a strong surge
of warm/moisture advection in the warm sector ahead of the cold
front, pushing high temperatures into the 80s for most with
dewpoints climbing into the 70s. Combined with steepening lapse
rates aloft, this could push instability values up to 2000-3000
J/kg with effective shear values around 35-40 knots.
Hodographs/model soundings show predominately unidirectional
winds with height above the lowest 1-2km, so quick growth to a
more linear storm mode would be favored. While damaging wind
gusts to 60 mph would be the main threat (15% chance) as storms
initiate in the mid-afternoon over north-central MN, the low-
level turning could be enough to produce a low-end embedded
tornado threat (2%) in the line as storms move eastwards into
northeast MN and NW WI into the evening. Large hail up to 1 inch
will also be a threat in these storms, but less so than the wind
threat. Storms should gradually weaken mid to late Tuesday
evening as they get farther into NW WI and lose a lot of the
instability with the loss of daytime heating.

Rainfall may be locally heavy on Tuesday under the stronger
storms, but the transient east-west movement of the cold front
and storms should limit the amount of time this heavy rainfall
falls in any one location. However, given rainfall from previous
rounds of rainfall, the total additional rainfall from this
evening through Tuesday will be a general 1-2 inches, with some
localized pockets to 3 inches. Where exactly the heaviest
rainfall with next two rounds of rainfall overlap still varies a
bit from model to model, hence the Flash Flood Watch not being
adjusted in coverage, but the best potential has shifted into
northern MN. Minor flooding/ponding will be the main concern as
a result of any heavy rainfall and runoff due to the decreasing
potential for 3+" of rainfall (<10%) limiting the risk for more
significant flash flooding to occur.

The warm temperatures and humidity will likely push Heat Index
values in NW WI to around 90 degrees on Tuesday afternoon. Not
quite to Heat Advisory levels, but still very muggy.

Wednesday - Early Thursday:

The Northland gets a break from the wet weather for a brief time
Wednesday through early Thursday as high pressure moves through
the region. Temperatures will be more pleasant both days, with
most locations seeing highs in the 70s.

Late Thursday - Next Weekend:

We see another shift to more active weather late Thursday into
this weekend as we get into another southwest flow pattern with
a warm front settling somewhere across the Upper Midwest late
week and then the main upper/surface low moving through the
region Saturday into early Sunday. Gulf of Mexico moisture will
also be surging north (PWATs 1.6-1.9" again) with this system.
Instability looks more weak to moderate, but enough to support
potential low-end strong to severe storm threats for our neck of
the woods on Saturday and Sunday. The main concern during this
period would be additional prolonged heavy rainfall potential
late week into the weekend. Still to early to pin down rainfall
amounts, but NBM probabilities of >1" Thursday-Sunday are
50-80%, with >2" sitting at 30-50% for much of the Northland,
though there are a non-trivial amount of GEFS and Euro ensemble
members with accumulations over 3". We will need to watch trends
with this late week/weekend system closely with future forecast
updates.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 642 PM CDT Mon Jun 17 2024

Generally VFR conditions across the area with high level clouds
aloft will track with us for next couple of hours before storms
and precipitation moves in from Southern MN. Through this
evening and into tonight, a warm front will move northward. This
will cause MVFR/IFR conditions to form from reduced ceilings
and visibility from the storms and increased moisture. Tied with
this frontal passage will be strong southerly winds with gusts
nearing 25-30kts. Lastly, there will be a notable amount of LLWS
for our entire area as a result of a prominent low level jet
moving into the area.

As morning arrives, most of the area
should see precipitation wind down except for INL where lower
ceilings and rain/drizzle will persist for an extended period of
time. Late tomorrow afternoon a cold front will move through
the area which will do two things. The first being -TSRA
conditions will be seen with rapid drops in visibility into the
MVFR and IFR range. Secondly following the front, winds late
tomorrow afternoon/evening will rapidly switch to come out of
the west.


&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 439 PM CDT Mon Jun 17 2024

Scattered shower and storm potential over western Lake Superior
very late this evening and tonight, though the threat for any
severe weather looks to remain west of the Lake. Better
potential for strong to severe thunderstorms late Tuesday
afternoon into evening as a line of storms develops along a
cold front in Minnesota and moves east over the Lake. Main
concerns would be wind gusts up to 50 knots with these storms,
though can`t rule out some hail up to 1 inch in diameter with
those storms, either.

Outside of storms, northeast winds on the Lake this evening and
tonight will increase to around 15 knots. Winds veer out of the
south ahead of the cold front tomorrow, with gusts approaching
25 to 30 knots in the Twin Ports and South Shore from late
Tuesday morning through evening, along with some brief winds to
25 knots along the North Shore in the evening with some 2-4 ft
waves. Therefore, have issued a Small Craft Advisory to account
for the period of hazardous conditions to small craft Tuesday
into Tuesday evening. Winds remain more tame Wednesday as drier
weather briefly returns under high pressure.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch through Wednesday morning for MNZ010-011-018-019-
     025-026-033>038.
WI...Flood Watch through Wednesday morning for WIZ001-006-007.
MARINE...Small Craft Advisory from 11 AM Tuesday to 1 AM CDT Wednesday
     for LSZ121-144>148-150.
     Small Craft Advisory from 9 PM Tuesday to 1 AM CDT Wednesday
     for LSZ140>143.

&&

$$

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