463
FXUS63 KDLH 151713
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1213 PM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are expected
  today into Wednesday. Rainfall amounts of 1-3" with locally
  higher amounts may lead to flash flooding concerns this
  afternoon into tonight in east-central Minnesota, the
  Arrowhead, and northwest Wisconsin.

- Strong to severe thunderstorms will be possible this afternoon
  and evening with damaging winds to 65 mph and large hail up
  to 1.5" in diameter being the primary hazards.

- Temperatures for the latter half of the week into the weekend
  will be more mild with additional chances for precipitation
  late Friday into Saturday.

&&

.UPDATE...
Issued at 1210 PM CDT Tue Jul 15 2025

Expanded the Flood Watch to include Aitkin County, as well as
most of the Arrowhead and Twin Ports in addition to the original
Flood Watch that had Pine County and most of northwest
Wisconsin. Latest high-res model guidance shows a concerning
signal for training convection along and just north of a
stationary front currently situated from the Brainerd Lakes
northeast into the Twin Ports and portions of the North Shore.
Expect thunderstorm initiation this afternoon, initially
starting as scattered discrete storms with a threat of large
hail to ping pong ball (1.5") size, 60 mph wind gusts, and heavy
rainfall that could lead to flash flooding. Latest atmospheric
parameters show PWAT values of 1.5-2" (higher side of
climatology for this time of year), MLCAPE of 1500-2500 J/kg,
and effective shear of 35-45 kt. Storms should grow upscale into
a southeastward-advancing line of storms, with the primary
threat transition to wind gusts of up to 65 mph, large hail to
quarter size, and heavy rainfall that could lead to flash
flooding as the line tracks into northwestern Wisconsin this
evening. Can`t rule out a low-end tornado threat for east-
central Minnesota into northwest Wisconsin late this afternoon
and evening as the 0-1km and 0-3km helicity appears a bit more
marginal, though there should be some low-level vorticity in the
vicinity of the front that could be stretched by strengthening
updrafts.

Particularly for the heavy rainfall potential: Storms should
repeatedly move over the same locations with efficient rates
(1-2"+ per hour), leading to concerns for Flash Flooding due to
rapid runoff. The latest HREF 12Z guidance shows 24-hour
localized probability matched mean QPF of 1-3" with localized
amounts to 4+ inches, with the best potential for the higher end
of these rainfall amounts where the Flood Watch has been issued
for. The flash flooding threat should transition into east-
central MN and northwest Wisconsin this evening as storms track
southeast with time.

&&

.DISCUSSION...
Issued at 526 AM CDT Tue Jul 15 2025

A line of thunderstorms has developed early this morning across the
northern portion of the CWA. 06z sfc analysis from WPC revealed a
warm front draped across northern MN, which has been the primary
forcing mechanism for this morning`s convection when combined with
the influence of a 30+ knot southwesterly LLJ at 850mb. This LLJ and
stalling warm front will continue showers and thunderstorms through
the early to mid morning hours today, mainly impacting northern MN.
High PWATs to around 1.7" as well as training storms this morning
has led to high rainfall rates and minor flooding concerns. In
addition, large hail to 1" will also be a concern for the next
several hours as MUCAPE values remain elevated in the 2000-2500 J/kg
range. Damaging winds are a minimal concern early this morning as
CAM model soundings show a stable layer in the low-levels and DCAPE
is only at 500 J/kg or less.

An active synoptic pattern is expected today as a series of
shortwaves propagate through the CWA within zonal flow at 500mb. At
the sfc, a quasi-stationary front over the CWA will provide
necessary forcing in additional to the larger synoptic lift. Deep
moisture advection is expected to occur today with PWAT increasing
to 1.5-2" by this afternoon, especially within the warm sector over
northwest WI and Pine County in MN. The orientation of this moisture
advection to the quasi-stationary cold front will likely result in
training thunderstorms developing this afternoon and continuing into
tonight as another LLJ around 30 knots in magnitude develops. CAMs
reflect this potential for training thunderstorms with decent
agreement on an overall pattern of training convection.

The primary concern for this afternoon into tonight is flash
flooding due to the high amount of PWAT, in the 90-97th percentile
per NAEFS and ECMWF climatology, and the potential for training
thunderstorms. Model soundings from the CAMs in KHYR show that a
deep warm cloud layer in excess of 10,000ft will be likely combined
with a long and skinny CAPE profile around 900-1200 J/kg. These two
factors are very favorable for heavy rainfall rates, which is
reflected in global ensembles showing signals for 1-3" inches of
rainfall by 12z Wednesday. In addition, probability matched mean QPF
from the 00z HREF suggest that locally higher amounts to 4" will be
possible over northwest WI, which could lead to flash flooding
concerns. With the ingredients in place for flash flooding, a Flash
Flood Watch was issued for most of northwest WI and Pine County in
MN due to the potential this afternoon through tonight. At this
time, the greatest uncertainty lies in exactly where these
training storms will develop due to spatial discrepancies in
the CAMs.

While flooding is the primary concern, severe thunderstorms will
also be possible this afternoon as instability increases in excess
of 1000 J/kg with 0-6km bulk shear of 20-30 knots. Primary severe
hazards this afternoon and evening will be large hail up to 1" and
sporadic wind gusts to 60 mph. A Slight Risk remains in effect for
portions of the CWA today due to this potential for strong to severe
thunderstorms. Overall, today into tonight will be a period to keep
an eye on the weather.

Precipitation will be slow to exit the CWA on Wednesday into
Wednesday night, with CAMs continuing to show additional rounds of
showers and thunderstorms on Wednesday. Wednesday`s precip will be
synoptically forced by a 500mb shortwave, which will move through
the CWA on Wednesday night. In the wake of this shortwave, a brief
period of high pressure will be possible on Thursday. This will
bring a brief break in the rain on Thursday before additional
chances for showers and thunderstorms arrive late Friday into
Saturday. Expect more mild high temps for the latter half of the
week into the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1210 PM CDT Tue Jul 15 2025

A stationary front will bring showers and storms this afternoon
and evening, with lingering showers and some embedded storms at
times overnight into Wednesday. Most of northeast Minnesota has
seen MVFR to IFR ceilings develop along and north of the surface
front, with some reduced visibilities due to smoke at INL, as
well, though VFR conditions are present elsewhere. Strong to
severe thunderstorms capable of producing large hail, damaging
winds, and heavy rainfall will be possible this afternoon and
evening, with intensity weakening tonight. Expect erratic and
gusty winds near any storms as well as quick reductions to
MVFR/IFR conditions with the storms and heavy rain. Expect IFR
to potentially LIFR ceilings to develop tonight behind the
front, lingering through the end of the TAF period at DLH,
east-central Minnesota, and northwest Wisconsin, while ceilings
improve a bit quicker at INL/BRD farther behind the front on
Wednesday morning.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 526 AM CDT Tue Jul 15 2025

Winds today will be around 10 knots or less before shifting
northeast and increasing on Tuesday night to 10 to 20 knots with
gusts to 25 knots, highest in the western arm and the Apostle
Islands. These winds will also generate waves in these areas of 2 to
5 feet. A Small Craft Advisory has been issued for these nearshore
waters starting late this evening. Winds then diminish to 5 to 15
knots on Wednesday night. Multiple rounds of thunderstorms are
expected today into Wednesday. A few stronger storms will be
possible this afternoon and evening across western Lake Superior.
Large hail and wind gusts to 50 knots are the primary concerns in
stronger storms along with cloud to water lightning and heavy
rainfall.

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 MNZ012-019>021-
     035>038.
WI...Flood Watch through Wednesday morning for WIZ001>004-006>008.
MARINE...Small Craft Advisory from 10 PM this evening to 7 PM CDT
     Wednesday for LSZ121-143>148-150.

&&

$$

UPDATE...Rothstein
DISCUSSION...Unruh
AVIATION...Rothstein
MARINE...Unruh