891
FXUS63 KDLH 130915 CCA
AFDDLH

Area Forecast Discussion...CORRECTED
National Weather Service Duluth MN
415 AM CDT Sat Jul 13 2024

.KEY MESSAGES...

- Hot temperatures again today. Perhaps cooler Sunday/Monday.

- Several chances of thunderstorms this weekend and Monday. Most
  likely time for strong to severe storms is today and tonight.

- Cooler temperatures return Tuesday. Chances of scattered
  showers and storms in store for next week.

&&

.DISCUSSION...
Issued at 406 AM CDT Sat Jul 13 2024

CORRECTED TO CHANGE THUNDERSTORM WIND GUSTS FROM KNOTS TO MPH.

Several areas of thunderstorms were ongoing early this morning
over northwest Ontario, southern Manitoba, the Dakotas, and west-
central Minnesota. The most organized of these was the complex
over northeast South Dakota, southeast North Dakota, and far west-
central Minnesota as of 0830Z. Those storms will continue to
propagate southeastward along an MUCAPE gradient fed by a
southerly 925 mb low-level jet. The northern periphery of the
storms will pass over the Brainerd Lakes area and possibly into
the Hinckley and Pine City areas before 14Z. That complex kicked
off an outflow boundary which stretched from near Detroit Lakes
northward toward Roseau. That feature may be of interest later
this morning.

The storms in northwest Ontario were gradually weakening and
becoming less organized over the past few hours. A southward
moving outflow boundary was noted on the Dryden radar and seemed
to be connected to weaker convection near Roseau and Warroad. That
feature will also bear watching over the next several hours.

Several possible scenarios for today`s forecast are in play.
Thunderstorms are likely, although the timing and location will be
dependent on how the ongoing convection evolves over the next 6
to 8 hours.

One scenario keeps convection over northwest Ontario into
northwest Minnesota percolating through late this morning and
propagating southeastward with time, moving into north-central
Minnesota by 14-15Z. In this scenario, diurnal heating this
morning will provide 1500-2000 J/kg of MLCAPE. Storms would
strengthen as they encounter this favorable airmass. Deep layer
shear will be limited, so storm-scale organization will be
dependent on cold pool dynamics rather than the background
kinematic fields. Storms in this case would accelerate
southeastward early this afternoon with severe weather possible
over the Arrowhead, east-central Minnesota, and northwest
Wisconsin. Wind gusts of 40 to 70 mph would be the main threat
from the storms with a smaller risk of hail up to ping pong ball
size.

Another scenario features weakening convection which dissipates
before reaching north-central Minnesota. In this scenario mostly
sunny skies would prevail across the area and would contribute to
very high MLCAPE values of 2500-3000 J/kg by mid- afternoon. The
remnant outflow boundary(ies) from the overnight convection would
likely be the source of low-level convergence and forcing for
ascent. In this scenario, 0-6 km bulk shear would increase to
30-40 knots prior to convective initiation. Favorable hodographs
would support supercells initially with a risk of large hail and
possibly tornadoes. With time, the storms would reinforce the
antecedent cold pool and merge into a forward propagating MCS.
Hazards would then transition to primarily damaging wind gusts of
40 to 70 mph as storms propagate southeastward across the
Northland.

In either scenario, there is a potential for locally heavy
rainfall and flooding. It would seem the risk of QLCS tornadoes is
low due to 0-3 km bulk shear of less than 30 knots. Storms would
move out of the Northland late this afternoon or this evening.

Temperatures today are expected to climb into the middle to upper
80s once again. There are, of course, concerns regarding storm
timing and cloud cover. If clouds and storms move into the area
late this morning, we`ll likely end up cooler than current
forecasts suggest, particularly over north-central Minnesota where
the warmest temperatures are expected.

Several high-res models feature additional redevelopment in the
wake of the first round of storms this evening or tonight. A
shortwave trough will develop aloft by this evening over the
Dakotas into the Canadian Prairies and push eastward toward the
Northland overnight. If the pattern of the past several nights
continues tonight, there should be sufficient destabilization and
forcing for ascent to support this second round of storms. A few
may be strong to severe once again with gusty winds and hail the
main threats.

By Sunday morning the upper-level shortwave trough axis will
depart the Northland. A brief period of height rises is forecast
which will help keep the risk of additional storms low through the
day. Temperatures will trend a few degrees cooler as the
convectively reinforced cold front slides to our southeast. The
front will stretch back west across North Dakota into Montana. The
western periphery of the front is forecast to become quasi-
stationary or perhaps lift northward again as a warm front late
Sunday afternoon.

A belt of stronger westerly flow aloft will develop Sunday night
over the Dakotas into central Minnesota which will support the
development of another shortwave trough. Thunderstorms are
forecast to develop along the front over North Dakota and Montana
during the late afternoon or early evening Sunday. That complex of
storms will generally push eastward overnight and may move into
northwest and north-central Minnesota between 10Z and 16Z Monday.
The earlier cold front may surge northward once again as a warm
front ahead of that storm complex. That round of storms could
strengthen late Monday morning into Monday afternoon with a few
strong to severe storms possible over the Northland. The front
will sag southward again Monday after another round of convective
reinforcement. The final passage of the cold front and the arrival
of northwest flow aloft in response to a broader upper-level
trough will bring an end to the severe thunderstorm risk.

Cold air advection will persist Tuesday with temperatures
dropping a few degrees below normal, though still in the seasonal
normal range. Isolated to scattered showers and perhaps a few
storms are possible despite the cooler temperatures.

Cyclonic flow and cold air advection aloft persists Wednesday.
Temperatures begin to trend warmer on Thursday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1258 AM CDT Sat Jul 13 2024

Thunderstorms over northwest Ontario, southeast Manitoba, and
the Dakotas have demonstrated a weakening trend over the past
few hours. Anvil clouds, in particular, have been dissipating.
Therefore clear skies are expected early this morning and I have
added MVFR visibilities at HYR and HIB. Winds will be light
overnight, between 2 and 5 knots, and we would need about an
hour of actual calm for fog to develop. High-res forecast models
have storms moving southeast and eventually strengthening again
late this morning into the afternoon. Have further refined the
precipitation chances with this forecast and opted for a window
of VCSH with PROB30 for the most likely time of thunderstorms.
As the line(s) of storms move past the terminals, expect strong
and gusty winds. Visibility may dip as low as LIFR for a time.
Opted for IFR visibility for now in the forecast. Another round
of storms is possible after 14.03Z. Due to very low confidence
in timing and location, I chose not to add second mention of
storms with this forecast.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 406 AM CDT Sat Jul 13 2024

Light offshore flow early this morning turns southwesterly away
from the shoreline. Surface high pressure Expect generally
light southwest winds of 10 knots or less to persist today.
Winds strengthen a little Sunday afternoon and remain from the
southwest. A cold front will pass southeastward over the waters
Monday afternoon. Winds are expected to strengthen to 10 to 15
knots and veer northwesterly in the wake of the front.

There is a chance of thunderstorms this afternoon, which may be
strong to severe. Wind gusts over 40 knots and frequent cloud-
to-water lightning are the main concerns. Another round of
storms is possible tonight and again ahead of the cold front
Sunday night or Monday morning.

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

&&

.HYDROLOGY...
Issued at 648 AM CDT Fri Jul 12 2024

A Flood Advisory continues across portions of the Rainy River
Basin, extending as far east as Lac La Croix and as far west as
the Rainy Lake outlet. This advisory has now been extended
through Monday afternoon. Lingering high water from rains in
June continue across the Rainy River Basin. The Vermilion River
continues to fall. Lake levels on Lac La Croix and Crane Lake
have crested, but are still elevated and slow to fall. Lake
Namakan looks like it is now cresting as of Friday morning.

All this high water continues to lead to slowing rises on
downstream lakes, notably Kabetogama (Kab) lake where minor
flooding continues, and on Rainy Lake where levels are still
exceeding the rule curve. Kab and Rainy Lake crests should
occur this weekend. This could bring Nam/Kab just under 1120
feet with a peak level somewhat similar to the high water during
the summer of 2014. This is still 2 feet or more below the high
water levels of Spring 2022 - we are nowhere close to that
level of flooding and extreme rises to that point are currently
not expected. As is usual for this basin, water will move slowly
and recessions will happen at glacial speeds with some flavor
of high water possibly continuing through the month. However,
peak should happen soon, based on latest observations.
Additional rainfall may cause brief rises in tributaries and
extend the period of high water in core lakes depending on where
and how much rain falls with several rounds of showers and
thunderstorms late tonight through Monday. Boaters should expect
high water, potentially hidden underwater hazards (including
submerged docks), and strong currents in constricted areas. Some
of the storms this weekend could be strong to severe, which
could lead to erratic gusts out of thunderstorms and impact wave
heights, as well.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
MARINE...None.

&&

$$

DISCUSSION...Huyck
AVIATION...Huyck
MARINE...Huyck
HYDROLOGY...Rothstein