041
FXUS63 KDLH 190553
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1253 AM CDT Thu Jun 19 2025

.KEY MESSAGES...

- Isolated to scattered thunderstorms will continue until around
  sunset today. A storm or two may be capable of producing small
  hail and locally gusty winds.

- Strong to severe thunderstorms will be possible on Thursday afternoon
  and again on Friday night. The best chance for widespread
  severe weather will be on late Friday evening into early
  Saturday morning.

- Hot and humid conditions are expected this weekend, with heat
  indices potentially reaching above 100 degrees. An Extreme
  Heat Watch is in effect.

&&

.DISCUSSION...
Issued at 339 PM CDT Wed Jun 18 2025

The latter half of this workweek into Saturday is expected to be an
active period of weather across the CWA.

TODAY:
A deep 500mb trough is currently propagating eastward across
the central CONUS today, developing widespread precipitation across
the lower Great Lakes. Locally in our neck of the woods, isolated
thunderstorms have developed around the St. Croix river valley this
afternoon roughly along a weak cold front. Upstream in the far
northwestern CWA, additional isolated to scattered thunderstorms
have developed along a secondary boundary. While far north-central
MN is highlighted under a Marginal Risk for severe thunderstorms
this afternoon, severe convection is unlikely today due to a small
CAPE profile appearing in model soundings and relatively weak 0-6km
bulk shear of 20-25 knots. While severe convection is unlikely,
gusty winds up to 50 mph may be possible around collapsing cells due
to deep mixing and steep lapse rates occurring in the sfc to 850mb
layer. This severe thunderstorm potential will diminish after sunset
as diurnal heating ends.

THURSDAY:
Additional 500mb impulses will be moving through the CWA on
Thursday as the overall flow aloft remains northwesterly. A
ridge building over the High Plains and a strengthening LLJ at
850mb will begin to provide WAA into the area and an overall
improved thermodynamic environment for severe convection. MLCAPE
will be increasing to the 800-2000 J/kg range by the late
afternoon hours, with highest values expected to occur in north-
central MN and the Brainerd Lakes area. Better 0-6km bulk shear
values to 50 knots will be favorable for the development of
convection. SPC currently has the CWA under a Marginal Risk,
with expected hazards being damaging winds to 60 mph and large
hail up to 1.5" in diameter. CAMs suggest that storm mode will
largely be discrete on Thursday afternoon/evening. Nearly
straight hodographs support splitting single cells (possible
supercells), shown in recent runs of CAMS. While hodographs are
not favorable for the development of tornados, especially
deviant right moving supercells post-split will still need to be
closely monitored for potential rotation. Expect storms to come
to an end late Thursday evening.

FRIDAY:
Friday and Friday night is the period of greatest concern in this
forecast update. The ridge that will be building over the High
Plains on Thursday will continue to strengthen on Friday. In
addition, the LLJ will begin to provide deep Gulf moisture advection
into the CWA, with PWAT potentially approaching as high as 2". For
context, max PWAT climatology for KINL is around 1.6". A shortwave
moving over top of the developing ridge, as well as a warm front
moving north into the CWA, will provide the necessary forcing for
convection. In terms of instability, MUCAPE will also be very
favorable with values in excess of 2000 J/kg possible.

While a lot of ingredients for severe convection will be in place on
Friday, there is a fair amount of uncertainty still regarding if
these ingredients will be able to come together during favorable
times. In addition, a sizable cap around 850-800mb appearing in
model soundings during the day and evening may limit the extent
of severe thunderstorm development. Finally, the current
expected timing for much of the severe convection will be late
Friday evening into early Saturday morning. This timeframe may
potentially leave these storms elevated, reducing the chance for
damaging winds or tornadoes.

Despite all of these potential failure points, Friday night`s
convection may become very impactful, especially if sfc heating
along the warm front becomes more robust than currently forecast. If
these storms on Friday and Friday night are able to become surface
based, all hazards are on the table including: tornados, damaging
winds, large hail, and flash flooding. If storms remain elevated,
primary hazards will be large hail and flash flooding. Currently,
the SPC has the CWA under a Slight Risk with a 10% hatched area
for significant severe storms. Given the favorable ingredients
that will be in place on Friday, upgrades in the Convective
Outlook are certainly possible. Friday into early Saturday
morning will be a period to keep a close eye on.

SATURDAY INTO EARLY NEXT WEEK: Following the warm frontal passage on
Saturday morning, strong WAA will occur across the CWA. This will
increase temperatures into the 80s and 90s across much of the CWA,
excluding areas immediately near Lake Superior along the North
Shore. Temperatures were increased above the NBM in the forecast
update this afternoon, as the deterministic NBM was on the
noticeably cooler end of probabilistic guidance. Since the majority
of probabilistic members had higher temps, both max and min Ts were
increased this weekend. This introduced heat indices in excess of
100 degrees for large portions of the CWA, especially on Sunday.
Given the potential for hot and humid conditions this weekend, an
Extreme Heat Watch was issued.

For those looking for relief from the heat this weekend, a cold
front will be fortunately passing through the CWA on Monday. This
will bring more seasonable temperatures back to the area for next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1253 AM CDT Thu Jun 19 2025

Clusters of showers and storms will continue to move through the
Northland overnight, although an overall decrease in intensity
and coverage should continue. Do not expect any impacts in the
first few hours of the 06Z forecast, but could need amendments
as convection continues overnight. Additional storms are
possible Thursday afternoon and evening, and some of those could
be severe. Wind direction will vary through the period, with
speeds less than 10kts, outside of stronger winds associated
with convection.

Patchy fog is possible through sunrise, with lowest vis across
northwest WI. At HYR, expect vis to drop as low of LIFR.
Elsewhere, fog development will depend on whether rainfall
occurs before sunrise.


&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 339 PM CDT Wed Jun 18 2025

Light winds expected through the period with minimal wave heights.
This evening high res guidance is hinting at some fog development
with a 50% chance of visibilities dropping below 1nm. If fog does
develop it is largely expected to disperse by mid morning with a 30%
chance of lingering through the day.

An active weather pattern begins tomorrow and persists through
Friday. There will be periodic chances for showers and storms. Some
storms may be strong to severe on Thursday and Friday in the
afternoon and evening hours.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Extreme Heat Watch from Sunday afternoon through Sunday
     evening for MNZ010>012-018-019-025-026-035-037.
     Extreme Heat Watch from Saturday afternoon through Sunday
     evening for MNZ033-034-036-038.
WI...Extreme Heat Watch from Sunday afternoon through Sunday
     evening for WIZ001>004.
     Extreme Heat Watch from Saturday afternoon through Sunday
     evening for WIZ006>009.
MARINE...None.

&&

$$

DISCUSSION...Unruh
AVIATION...HA
MARINE...Britt