324
FXUS63 KDLH 182224 AAA
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
524 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- Showers and thunderstorms expected tonight into Thursday. An
  isolated severe thunderstorm is possible over central and
  north- central Minnesota overnight.

- Thursday afternoon into the evening, a second round of
  thunderstorms are expected to initiate along a cold front,
  with scattered severe storms possible. Large hail, damaging
  winds, a couple tornadoes, and locally heavy rain may occur.

- Seasonable temperatures may return through the weekend and
  into next week.

&&

.MESOSCALE UPDATE...
Issued at 525 PM CDT Wed Sep 18 2024

A band of showers and a few embedded thunderstorms stretched
from near Red Lake to near Grand Rapids to the Twin Cities as of
515 PM CDT and were moving north-northeast at 35 mph. This band
of precipitation developed along the ascending branch of an 850
mb frontogenetic circulation on the northern periphery of a
zone of stronger southerly 850 mb flow over western Minnesota
and eastern North Dakota. Instability is quite limited in this
area per the 22Z SPC RAP Mesoanalysis. MUCAPE is less than 1000
J/kg and MLCAPE is less than 500 J/kg. Nevertheless, the
vigorous upward vertical motion supported some low-centroid
storms over central Minnesota, embedded near the middle of the
overall precipitation band.

The 21Z RAP forecast has this feature continuing to lift north-
northeastward across Koochiching, Itasca, and northern St.
Louis county through early evening. There has been a recent
weakening trend with the showers and particularly the storms.
Think that trend will persist through 8 PM.

Thereafter, there is still a potential for storms to redevelop
later this evening and overnight as a southerly low-level jet
strengthens and expands over western Minnesota and the eastern
Dakotas.

&&

.DISCUSSION...
Issued at 211 PM CDT Wed Sep 18 2024

Another hot and muggy day has developed across the Northland with
southerly flow bringing temperatures in the 80s and dewpoints in the
60s for much of the region. An approaching warm sector from a low
pressure system coming out of the Northern Rockies is throwing an
area of clouds and some showers over the Dakotas and western
Minnesota early this afternoon. Those showers are expected to
continue into north-central Minnesota later this afternoon and
evening, with a boost by the LLJ overnight. This could lead to some
elevated convection for the Brainerd Lakes to the International
Border around midnight. With 1000-1500 J/kg of MLCAPE and around 30
knots of bulk shear, there may be an isolated severe storm of two in
this convection, capable of briefly producing some large hail and
damaging winds. As this area of showers and thunderstorms pushes
northeast and outruns the best forcing as the LLJ is waning,
precipitation coverage should decline through mid morning.

As the stacked upper level low continues to progress along the
International Border, a cold front should continue to march from west
to east through the day, eventually leading to a secondary round of
thunderstorms igniting in the afternoon. Morning precipitation could
lead to some widespread mid to high clouds which should delay the
time of ignition until late afternoon. Most CAMs have come into semi
decent agreement for storm ignition in the 3-5pm timeframe along a
north-south line. There is still some disagreement about the
position of this line, but based on latest trends it`s likely to be
past Brainerd-International Falls. These afternoon storms should be
surface based, with a seasonably strong, moist airmass to support
them. A narrow zone of 1500-3000 J/kg of MLCAPE, 30-40 knots of bulk
shear perpendicular to the front, 6-8 C/km low level lapse rates,
and well curved low level hodographs should support a discrete mode
initiation with quick upscale growth and supercell potential. Large
hail up to 2" in diameter may be one of the favored hazards early
on, benefiting from late afternoon instability and that quick
upscale growth. All hazards are on the table however, with a
damaging wind threat increasing through the event as the line may
begin to tend towards clustering. A tornado or two is possible as
long as storms remain surface based, with models showing a potential
plume of 100-125 m2/sec2 of 0-0.5km helicity. In addition to the
severe threat, some quick downpours and locally heavy rain is
possible, thanks to our very moist environment. However, no
widespread heavy rainfall coverage is expected.

Beyond Thursday, the Northland finds itself stuck between a high
pressure over the southern Plains and an upper level trough bearing
down from Canada. Embedded within that all could come some cut off
lows and shortwave troughs. This should generally bring some cooler
temperatures to the region, but our current above normal temperature
situation may dally on it`s way out, with high temperatures not
expected to reach their climatological normal of high 60s until
Sunday. All the action in the upper levels may also keep chances for
rainfall around. However, by and large global ensembles have backed
off from a  widespread washout precipitation solution, so there
could be some sunshine scattered in there as well.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 630 AM CDT Wed Sep 18 2024

A few isolated showers across MN this morning as the LLJ weakens.
Through the day we are expecting VFR conditions with some gusts out
of the south upwards of 20 kts. The latest models runs have been
backing off the storm chances for this afternoon and making it more
of an overnight feature. We will also have the LLJ to contend with
once again bringing low level shear across the region once again
overnight.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 211 PM CDT Wed Sep 18 2024

Southerly winds along the South Shore turn and become onshore for
the Twin Ports and North Shore again today, with some gusts of 10-15
knots possible in the afternoon. Thursday, slightly stronger south
to southeast winds are possible, sustained around 10-15 knots and
some gusts near 20 knots in the Twin Ports and Chequamegon Bay. Rain
showers and thunderstorms are likely Thursday, which may contain
strong winds and large hail in the afternoon and evening. Friday,
expected southwesterly winds with some breezy afternoon gusts behind
Thursday`s cold front.

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.

&&

$$

MESOSCALE...Huyck
DISCUSSION...Levens
AVIATION...Levens
MARINE...Levens