382
FXUS63 KDLH 200319
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1019 PM CDT Thu Sep 19 2024

.UPDATE...
Issued at 1018 PM CDT Thu Sep 19 2024

Thunderstorm intensity and coverage has dropped off considerably
late this evening as the atmosphere has been stabilizing with
surface-based CIN beginning to increase with the loss of daytime
heating. Severe weather no longer expected for the remainder of
the evening to early overnight hours, though we may need to
watch for far southern Price County being on the northern
periphery of the path of some scattered storms currently near
Eau Claire in the next 1-3 hours as the low-level jet increases
to around 40 kts late this evening/early overnight, with a low-
end chance for sub-severe gusty winds and small hail out of
those storms. Otherwise, widely scattered showers and a few
storms over the MN Arrowhead and parts of NW WI will continue
tracking northeast over the next few hours ahead of a eastward
moving cold front, with precipitation exiting east of the area
early tonight.

&&

.KEY MESSAGES...

- Strong to severe thunderstorms are ongoing across parts of
  northeast Minnesota and northwest Wisconsin, with storms
  gradually weakening and tracking east through the evening.

- Another chance for showers and thunderstorms on Saturday. Depending
  on timing and placement, a few strong storms could occur.

- Seasonable temperatures return Sunday and into next week.

&&

.DISCUSSION...
Issued at 145 PM CDT Thu Sep 19 2024

As expected, a stacked upper level low continues to steadily march
along the International Border this afternoon, pushing a north-south
cold front into and across Minnesota. As instability builds and our
cap erodes, quick upscale growth is expected as storms ignite along
the cold front, taking advantage of 2000-3000 J/kg SBCAPE and 25-
40knots bulk shear. Storms are expected to ignite first in southern
Minnesota and unzip to the north through the Twin Ports. A secondary
area of storms closer the upper level low should also pop off across
the Iron Range and into the MN Arrowhead. CAMs are still in decent
agreement for ignition in the Northland in the 4-6pm timeframe, then
pushing east through 10-11 PM across the Arrowhead and NW WI.

Across the board, large hail, damaging winds, and a couple tornadoes
are possible hazards. An initially discrete mode is expected to
become kind of messy as it evolves into clusters. Bulk shear is
expected to wane into the evening hours, reducing the chance for a
true QLCS type system to be realized. The one exception might be in
the MN Arrowhead where locally high shear close to the low could
help more of a linear system come to fruition. Slightly more backed
winds in the northern portion of the CWA could lead to enhanced SRH
and better low level curvature in hodographs, which will need to be
monitored for an isolated tornado threat. Otherwise marginal SRH and
already fairly southerly winds further south may lead to a reduced
tornado threat. Large hail up to ping pong size in diameter remains
possible, especially in the first couple hours of convection
initiation. Damaging winds up to 60 mph are possible, especially
with any more linear clusters or decaying storms. In addition to the
severe threat, some quick downpours and locally heavy rain is
possible, thanks to our very moist environment. PWATs at
International Falls were 1.46 inches this morning, which is a new
daily max for the 12z sounding. Some high rainfall rates are likely
with storms, and were already observed in some of our morning
convection. However, with antecedent dry conditions, 1 hour flash
flood guidance is 2-3 inches across much of the area expected to see
heavy rain this afternoon and evening, so we would need very
impressive rates in order to get any minor flooding.

Beyond today, the Northland finds itself stuck between a high
pressure over the southern Plains and an upper level trough bearing
down from Canada. Global models have come into better agreement on
an oblong trough brushing over northern Minnesota Saturday, bringing
our next chance of precipitation, most likely in the afternoon and
evening. Some instability is present and if the cap can be eroded a
cold front would have access to over 1000 J/kg of MUCAPE (mostly in
NW WI) which could produce some stronger afternoon thunderstorms.
Much to the approbation of summer lovers, above normal temperatures
are expected to continue through Saturday with highs rising into the
70s and low 80s. We are still on track to see more normal
temperatures return Sunday behind Saturday`s front with highs in the
60s and overnight lows in the 40s and 50s. These relatively cooler
temperatures should continue into next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 641 PM CDT Thu Sep 19 2024

Thunderstorms will impact several TAF sites this evening, with
patchy fog developing overnight as storms diminish. A period of
gusty west winds and scattered clouds Friday afternoon.

In the next few hours, strong to severe thunderstorms will
impact DLH and HYR causing reductions to IFR or worse conditions
as heavy rain, strong winds, and possible hail impact at DLH
00z to 02z or so and HYR around 01z to 04z. Elsewhere VFR
conditions will prevail this evening, with patch fog developing
at HIB and HYR causing reductions to MVFR visibility. Fog will
quickly lift on Friday morning, but low level moisture will
cause initially MVFR stratocumulus clouds to develop at INL and
possibly HIB on Friday morning into the afternoon, lifting to
VFR ceilings before eventually clearing out. Otherwise
conditions at other sites remaining VFR through the day Friday.

South to southwest winds around 5 knots overnight becoming
westerly around 10 knots gusting to 15-20 knots on Friday.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 1018 PM CDT Thu Sep 19 2024

Thunderstorms should be past Western Lake Superior by around
midnight and winds begin to turn southwesterly. Friday,
expected southwesterly winds with some breezy afternoon gusts
behind today`s cold front. Some gusts of 15 to around 20 knots
are possible, but Small Craft Advisory criteria are not expected
to be met at this time. South to southwest winds continue
Saturday, mostly less than 10-15 knots, and there is a chance
for some showers and thunderstorms in the afternoon and evening.
Winds become northwesterly Sunday, fairly light around to less
than 10 knots.

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...None.

&&

$$

UPDATE...JJM
DISCUSSION...Levens
AVIATION...JJM
MARINE...Rothstein