Severe Thunderstorm Warning 86, NWS Duluth, MN

Area Forecast Discussion
National Weather Service Duluth MN
1155 PM CDT Thu Jul 25 2019

.SHORT TERM...(This evening through Friday night)
Issued at 352 PM CDT Thu Jul 25 2019

A cold front was located over southeast Manitoba, northwest
Minnesota, and portions of the eastern Dakotas late this
afternoon. A cutoff low was trailing the cold front over
Saskatchewan and Manitoba. Along and ahead of the boundary a
moderately unstable airmass has developed with a ribbon of 2-3
kJ/kg MLCAPE oriented along the front. Storms have developed ahead
of the front on the gradient of this instability gradient. Deep
layer shear is modest, generally between 25 to 30 knots in the 0-6
km layer. Even so, storms pulse storms are possible with large
hail and damaging wind gusts as the main severe weather threat.
The storms will likely progress eastward and will affect the
northern half of our forecast area this evening. The risk of
severe weather will continue through this evening before storms
weaken with the loss of daytime heating. Should storms remain
intact through 06Z, a strengthening low-level jet over northwest
Wisconsin and portions of the Minnesota Arrowhead may reinvigorate
the storms during the early morning hours of Friday. The cold
front will advance slowly across the Northland Friday afternoon
and evening. Depending on the evolution of the storms tonight, and
whether they linger through late Friday morning, there is a
potential for another round of strong to severe storms Friday
afternoon and evening. GFS and ECMWF guidance points to 1500-2000
J/kg of MLCAPE by afternoon with stronger bulk shear of 35 to 40
knots in the 0-6 km layer and 45 to 50 knots in the 0-8 km layer.
Destabilization will be dependent on clouds and precip clearing
out of the area by late morning. Large hail and gusty winds are
possible once again, should sufficient instability develop. We
agree with the SWODY2 Marginal Risk for severe storms, pending the
evolution of tonight’s weather. Storms will clear out of the
Northland Friday evening with clearing skies expected.

.LONG TERM...(Saturday through Thursday)
Issued at 352 PM CDT Thu Jul 25 2019

Mild this weekend with a chance for showers and storms late
Sunday into early Monday, then dry and seasonable to below normal
temperatures early to mid next week. It will be absolutely
gorgeous early next week with dew points falling into the 40s and
lows possibly touching the upper 30s on Tuesday morning in a few
spots across northeast Minnesota! The rest of the week looks
fairly dry - a weakening warm front may bring a low chance for
precip mid-week, then a stronger cold front approaches late-week
into next weekend with the next good chance for widespread
precipitation.

On the synoptic scale a weak mid/upper level ridge will build
across the Upper Midwest and Great Lakes Saturday resulting in
mainly sunny skies with near to above normal temperatures. A
deepening mid-level shortwave trough will approach from the west
across southern Canada, with a surface cold front extending down
into the eastern Dakotas late Saturday into Minnesota on Sunday.
Given the low level moisture advecting from the south ahead of the
front and the slowing trend in the fronts arrival in run-to-run
model trends, there may be sufficient large-scale lift and surface
heating to break the cap and cause scattered to widespread
showers and storms Sunday afternoon into Sunday night across the
Northland. Very weak winds through the low and mid levels of the
atmosphere and fairly limited instability will lead to weak storms
with a slow storm motion, and at this point severe storms appear
unlikely. Highs in the low 80s Saturday and Sunday.

Some showers and storms may linger into Monday morning, then a
strong area of high pressure builds in across the Great Plains and
Upper Midwest associated with a mid/upper level shortwave ridge
behind the trough. A broad upper high then builds across the Four
Corners region mid-week, with the mid/upper level ridge building
over the High Plains by late week. With a much cooler airmass in
place across the Upper Midwest, temperatures will be near to below
normal with dry conditions anticipated for much of the work week.
Highs in the low to mid 70s Monday, then a gradual warming trend
with highs in the mid 70s to low 80s through the rest of the work
week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1151 PM CDT Thu Jul 25 2019

All kinds of cloud debris out there will make for a tough forecast
particularly for flight conditions. Entire forecast depends on if
more convection lights up in the next few hours as some models
suggest along a rich convective boundary. So far, not enough
organization to spark this off, so kept a mention in southern TAF
sites. LLWS a bit of an issue in NW WI. Winds will be gusty again
on Friday.

&&

.MARINE...
Issued at 1010 PM CDT Thu Jul 25 2019

A persistent southwest wind will lead to building waves along the
North Shore. Waves may build as large as 3 to 5 feet north of
Grand Marais, a Small Craft Advisory may be needed late tonight
through Friday evening. Winds and waves gradually diminish into
Saturday as an area of high pressure builds in.

A chance for thunderstorms across western Lake Superior late
today into tonight, then again Friday afternoon into Friday
evening. A few strong to severe storms are possible.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  62  84  60  84 /  60  40  30   0
INL  62  80  56  82 /  60  50  20   0
BRD  64  87  62  86 /  50  10   0   0
HYR  62  82  61  85 /  50  50  40   0
ASX  64  84  63  86 /  50  50  40   0

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

SHORT TERM...Huyck
LONG TERM...JJM
AVIATION...Wolfe
MARINE...Wolfe

Hazardous Weather Outlook
National Weather Service Duluth MN
1156 PM CDT Thu Jul 25 2019

MNZ010>012-018>021-025-026-033>038-WIZ001>004-006>009-270500-
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-
1156 PM CDT Thu Jul 25 2019

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

.DAY ONE...Tonight

Scattered thunderstorms will move through northern and central
Minnesota into the Minnesota Arrowhead and northwest Wisconsin by
late tonight. Some storms in northern and central Minnesota may be
severe with large hail, damaging wind gusts, heavy rain, and
frequent cloud-to-ground lightning.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Scattered thunderstorms are possible Friday and Friday evening.
Strong to severe storms are not out of the question, but will
depend on skies clearing during the morning through early
afternoon hours.

There is a chance for thunderstorms Sunday into Sunday night
across the Northland. Storms are not expected to be severe.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotter activation is not anticipated tonight.

LSZ121-140>148-270500-
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-
1156 PM CDT Thu Jul 25 2019

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

.DAY ONE...Tonight

There is a chance for thunderstorms across much of western Lake
Superior late this afternoon into tonight. A few storms could be
strong to severe. These winds will lead to building waves along
parts of the North Shore, especially north of Grand Marais.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Persistent southwest winds at 10 to 15 knots on Friday may lead
to increasing wave heights on the north shore, especially north of
Grand Marais. A Small Craft Advisory may be needed.

Another chance for thunderstorms across western Lake Superior on
Sunday afternoon into Sunday night. Severe storms are not
anticipated.

Wolfe

More information may be obtained at the following web address:
http://www.weather.gov/duluth (all lower case)

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