Flash Flood Warning 7, NWS Duluth, MN

Area Forecast Discussion
National Weather Service Duluth MN
624 PM CDT Tue Jun 18 2024

.KEY MESSAGES...

- Strong to severe thunderstorms are likely to develop this
  afternoon and evening. Hazards include damaging winds to 70
  mph, large hail up to 1.75", locally heavy rainfall possible
  leading to flash flooding, and a chance for a tornado or two.

- Much of the Northland is under a Slight Risk (2 out of 5) for
  severe weather today. Storms will be beginning early this
  afternoon today and move east-southeast through the afternoon
  and evening.

- Cooler temps and high pressure on Wednesday will lead to quiet
  conditions. Additional shower and thunderstorm chances likely
  later this weekend into this upcoming weekend.

&&

.DISCUSSION...
Issued at 155 PM CDT Tue Jun 18 2024

This afternoon and evening:

Today is a fairly complex setup, which will be leading to a
conditional threat for severe weather development this afternoon and
evening. 15z surface analysis shows a stationary front located over
northwestern Minnesota, which will be the main source of lift this
afternoon and evening. A negatively-tilted shortwave trough will be
propagating through the northern Great Plains this afternoon and
evening, providing the necessary synoptic forcing to transition the
stationary front into a cold front that will through the CWA. Ahead
of this approaching cold front, a warm front draped across the CWA
from south of Brainerd, up to the Iron Range, and then south towards
the Twin Ports has been firing off scattered to widespread showers
and storms in portions of northeast and north-central Minnesota.

One of the most impressive ingredients with today's severe weather
threat is the high amounts of precipitable water. The 14z
sounding from INL recorded a PWAT of 1.41", which comfortably
places it above the 90th percentile of climatology. Dewpoints
have already been rising into the low 70s across southern
portions of the CWA early this afternoon. Strong southerly flow
provided via a LLJ of 35-40 knots will help advect this deep
moisture northward. Despite persistent cloud cover this
morning, this moisture and warm air advection provided via the
LLJ is expected to help destabilize the atmosphere by this
afternoon across the majority of the CWA. MLCAPE by mid to late
this afternoon will be building around the 1500-2500 J/kg range.
Favorable 0-6km bulk shear of 35-45 knots will help provide
organization to the expected convection later this afternoon.

All severe weather hazards will be possible this afternoon,
including damaging winds up to 70 mph, large hail up to 1.75",
locally heavy rainfall leading to flooding, and a tornado or two.
The tornado potential this afternoon will be contingent on the
amount of discrete convection that can form before storm mode
switches more linear as the storms move into northwest Wisconsin.
High amounts of 0-1km SRH of 200+ m2/s2 present around and south of
the Iron Range and low LCL heights continuing through the afternoon
supports the potential for a tornado or two late this afternoon into
early this evening. As storm mode switches to more linear this
evening, which is supported by the majority of CAMs, tornado concern
will transition towards possible QLCS tornados in the Arrowhead and
Douglas, Burnett, and Washburn early this evening. However, this is
much less of a concern compared to the discrete supercell potential
late this afternoon into the early evening.

One other primary concern with today into tonight's storms is the
flash flooding potential. Antecedent soil moistures are already
saturated across much of the NE MN portion of the CWA, where
1-3" of rain has fallen over the past 24 hours. Additional
rainfall amounts of 2-6" will be possible this afternoon into
tonight as upscale growth leading to training storms occur along
the warm front mainly along and north of U.S. 2 in MN. Since
there has been an increasing trend in QPF in the 12z runs, the
Flood Watch has been expanded to include the inland portions of
Lake and Cook County.

The severe weather potential is expected to decrease this evening as
the storms propagate farther east into northwest Wisconsin, where
instability will be decreasing and shear will be less favorable.

Wednesday through Wednesday night:

After the cold front sweeps through tonight into tomorrow morning,
quieter weather will move in on Wednesday as high pressure builds
over the region. Temperatures tomorrow will be noticeably cooler
with highs in the low to mid 70s for most.

Thursday through the weekend:

The pattern resumes its active behavior with southwest flow bringing
another large system through the region starting Thursday and Friday
with a warm front before a stronger low moves through for Saturday
into Sunday. Ample moisture will move into the region from the Gulf
of Mexico with PWATs rising to near the top of climatology once
again. Instability continues to look anemic during much of this time
period with the heavy rainfall threat being more of a concern. NBM
probabilities have not changed much with chances of an inch or more
slightly increasing to around 60 to 80% and chances for 2 inches or
more at 30 to 50%. Given the rainfall currently occurring, many
areas will be primed to be mainly runoff with saturated ground and
already high rivers and streams.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 624 PM CDT Tue Jun 18 2024

An area of thunderstorms, some of them severe, is moving across
the area this evening, and is expected to continue through no
later than 06z tonight. The strongest storms may produce LIFR
visibilities and IFR ceilings, along with large hail and strong
gusty winds. Storms will weaken beginning around 03z before
moving out of the area. IFR ceilings are expected overnight with
lingering light rain showers until 12z. Northwest winds and
clearing skies are expected behind the front, with all sites
returning to VFR in the 12z-18z time frame.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 356 PM CDT Tue Jun 18 2024

Periods of showers and storms are expected over western Lake
Superior this afternoon and evening. Strong to severe storms
will be possible this afternoon and evening with wind gusts over
40 knots along with hail over 1 inch in diameter possible. A
cold front will work across the western part of the lake this
evening with storms expected to end following the passage of the
front.

Winds outside of any storms this evening ahead of the cold
front will be southerly at 5 to 15 knots with gusts to 20 to 25
knots, highest near the Twin Ports. These winds will also
generate waves of 2 to 5 feet along the North Shore. Small Craft
Advisories remain in effect for all of the nearshore waters for
today into tonight. Behind the cold front, winds will become
westerly tonight into Wednesday, gradually diminishing to 15
knots or less by mid morning Wednesday. High pressure moves in
Wednesday.

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 MNZ010>012-018-019-
     025-026.
WI...None.
MARINE...Small Craft Advisory until 1 AM CDT Wednesday for LSZ121-
     144>148-150.
     Small Craft Advisory until 1 AM CDT Wednesday for LSZ140>143.

&&

DISCUSSION...Unruh
AVIATION...LE
MARINE...LE

Hazardous Weather Outlook
National Weather Service Duluth MN
803 PM CDT Tue Jun 18 2024

MNZ010>012-018>021-025-026-033>038-WIZ001>004-006>009-200115-
Koochiching-North St. Louis-Northern Cook/Northern Lake-
North Itasca-Central St. Louis-Southern Lake/North Shore-
Southern Cook/North Shore-North Cass-South Itasca-South Cass-
Crow Wing-Northern Aitkin-South Aitkin-Carlton/South St. Louis-
Pine-Douglas-Bayfield-Ashland-Iron-Burnett-Washburn-Sawyer-Price-
803 PM CDT Tue Jun 18 2024

This Hazardous Weather Outlook is for portions of northeast
Minnesota and northwest Wisconsin.

.DAY ONE...Tonight

Periods of moderate to heavy rain are ongoing across most of
northeast Minnesota with impacts from flooding being observed.

Isolated strong to severe thunderstorms continue through late this
evening. Primary hazard is a lone tornado or wind gust to 60 mph in
east-central Minnesota.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Additional rain and thunderstorms are expected late-week into
this weekend. Heavy rain and some flooding issues are possible.

.SPOTTER INFORMATION STATEMENT...

Reports of rainfall and flooding from spotters and the public are
requested.

LSZ121-140>148-150-200115-
Bayfield to Oak Point WI-Grand Portage to Grand Marais MN-
Grand Marais to Taconite Harbor MN-
Taconite Harbor to Silver Bay Harbor MN-
Silver Bay Harbor to Two Harbors MN-Two Harbors to Duluth MN-
Duluth MN to Port Wing WI-Port Wing to Sand Island WI-
Sand Island to Bayfield WI-Oak Point to Saxon Harbor WI-
Outer Apostle Islands Beyond 5 NM from Mainland-
803 PM CDT Tue Jun 18 2024

This Hazardous Weather Outlook is for portions of Lake Superior
and the Nearshore waters of western Lake Superior.

.DAY ONE...Tonight

Strong south winds with gusts up to 25 knots and waves up to 3
feet are expected this evening. A Small Craft Advisory is in
effect. Dense fog has been observed this evening and is expected
to continue into early Wednesday morning.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

The probability for widespread hazardous weather is low.

NLy

More information may be obtained at the following web address:
http://www.weather.gov/duluth

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