454
FXUS63 KDLH 130527
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1227 AM CDT Thu Jun 13 2024

.KEY MESSAGES...

- Strong to severe thunderstorms is ongoing this evening. Hazards
  include very large hail up to 3" in diameter, damaging winds
  to 70 mph, and a few tornadoes.

- Cooler temps on Thursday and high pressure on Friday.
  Additional shower and thunderstorm chances likely this weekend
  into early next week.

&&

.DISCUSSION...
Issued at 140 PM CDT Wed Jun 12 2024

This afternoon and evening:

Destabilization has been occurring early this afternoon as skies
have (or in the process of becoming) cleared in the wake of showers
and thunderstorms that moved through earlier this morning. High
MLCAPE values of 2000-3500 J/kg are expected this afternoon and
evening in the warm sector ahead of an approaching cold front.
Aloft, a steep elevated mixed layer around 8-8.5 degC/km will be
advecting into the CWA this afternoon. At the surface, moisture
advection provided via a strong southwesterly LLJ at 850mb of 40-45
knots has increased dewpoints across the MN portion of the CWA
to around the low to mid 60s.

Previously, there was some concern that the convection that is
currently moving through southern MN would reduce the amount of
available moisture and reduce the severe thunderstorm potential.
However, recent obs have shown that the strong LLJ has been able to
overcome this barrier. Latent heat release from the morning and
ongoing convection being advected northward is also likely
contributing to the strong instability that will be seen today.

Thunderstorms are expected to have strong and quickly-developing
organization today as very favorable wind shear occurs over the CWA.
A strong 500mb jet maxima will result in 0-6 km bulk shear today of
50-55 knots. Storm mode today is expected to initially begin as
discrete supercells over north-central MN, primarily northwest of
the Iron Range. As convection propagates eastward, storm mode is
expected to transition to becoming more quasi-linear. Recent runs of
the CAMs suggest that while storm mode will become more linear this
evening, large hail will continue to be a threat as cells remain
somewhat discrete. Timing wise, strong to severe convection will be
starting as soon as 3 PM in far north-central MN and move east-
southeast through the region this afternoon and evening. Any
strong to severe thunderstorms should be downstream of the CWA
around midnight tonight.

All severe thunderstorm hazards will be possible this afternoon and
evening, expect for flash flooding. The primary concern is very
large hail, which is forecast to be up to 3 inches in diameter
across the MN portions of the CWA and adjacent counties in northwest
WI. Damaging winds up to 70 mph are also a concern today, as model
soundings show dry air in the low-levels and DCAPE values of around
1000-1500 J/kg. While the potential is low, a tornado or two also
can`t be ruled out this afternoon and early evening as 0-1km SRH
increases to around 100-150 m2/s2. The one limiting factor to the
tornado potential today will be somewhat high LCL heights of around
2000 feet AGL in the area where discrete supercells are most likely
in far north-central MN. LCL heights will be lowering to around 350-
750 feet AGL farther east late this afternoon and evening, but with
storm mode becoming more linear, this will lessen the tornado
threat. Flash flooding is unlikely to occur today as the strong to
severe thunderstorms will be fairly progressive across the CWA.

Thursday into Friday:

Cooler temps are expected tomorrow following the cold frontal
passage tonight. Scattered showers will be possible, mainly in the
Arrowhead. Isolated thunderstorms in the afternoon hours will be
possible, but severe weather is not expected. Quiet conditions
develop on Friday as high pressure builds over the Northern Plains.

Weekend into early next week:

Low pressure developing in the lee of the Rockies Friday evening
will propagate into the Upper Midwest on Saturday. This will be
bringing widespread showers and thunderstorms through much of the
weekend. Strong WAA occurring over the weekend will result in high
temps on Sunday reaching into the low to mid 80s with uncomfortable
dewpoints in the 60s. Monday will see shower and thunderstorm
activity continue as a strong shortwave trough propagates eastward
through the central CONUS. There are early indications that Monday`s
system could bring strong to severe thunderstorms, especially in
north-central MN. However, it is still too early for specifics.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1227 AM CDT Thu Jun 13 2024

Thunderstorm activity is starting to wane this morning with the only
cell still in our area over Itasca. Storm track motion puts this
cell through HIB shortly after TAF time. This cell could produce some
pea sized hail. Fog may develop later this morning and linger a few
hours after sunrise. After the fog clears we expect VFR conditions
through the day. Some diurnally driven cumulus and showers with some
isolated storms will be possible in the afternoon. Winds will also
be gusty out of the northwest.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 140 PM CDT Wed Jun 12 2024

Strong to severe storms may produce hail and gusty winds across
western Lake Superior this late afternoon and evening ahead of a
cold front. Following the cold frontal passage, winds increase out
of the northwest on Thursday with gusts to near 20 knots - a Small
Craft Advisory may be needed. Winds weaken Thursday evening into
Friday as an area of high pressure builds across the Upper Great
Lakes. This weekend into early next week a more active weather
pattern develops with a few chances for precipitation.

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...Dense Fog Advisory until 10 AM CDT this morning for LSZ140>142.
     Small Craft Advisory from 10 AM this morning to 7 PM CDT this
     evening for LSZ143>145.

&&

$$

DISCUSSION...Unruh
AVIATION...Britt
MARINE...JJM