Severe Thunderstorm Warning 15, NWS Duluth, MN

Area Forecast Discussion
National Weather Service Duluth MN
101 PM CDT Sun Jun 21 2020

.UPDATE...
Issued at 101 PM CDT Sun Jun 21 2020

Parts of northeast and east central MN and parts of northwest WI
have destabilized nicely this afternoon, with CAPE values around
1000j/kg, with bulk shear values in the 35-40 knot range. With the
cold front moving into the area, thunderstorms have already
developed from just south of Ely southwest through Grand Rapids,
with additional interesting elements on satellite toward Brainerd.
Expect additional development the next few hours from these areas
on east, and we may have a few strong to severe storms.

&&

.SHORT TERM...(Today through Monday)
Issued at 444 AM CDT Sun Jun 21 2020

This morning, a shortwave rotating around the upper level low
sitting over Manitoba is bringing a band of light rain showers
across northern MN. Farther east in NW WI, the rapid clearing of
cloud cover overnight combined with the saturated surface has
generated fog with locally dense areas having visibility reductions
of less than a quarter mile.

The showers that are currently moving through the Northland are
expected to slowly diminish this morning with partly sunny skies
breaking through and highs expected in the mid to upper 70s. The
dense fog over NW WI is also expected to disperse around 9am.

Another round of showers/storms are expected to populate across the
Northland again this afternoon. A split jet flow aloft will help to
support two systems propagating through the area. A cold front
entering from the west and a surface low moving northeast out of the
the central plains will fire off some additional precipitation
chances. There is potential for some strong storms producing large
hail and damaging winds primarily over NW WI and westward toward
Brainerd. The SPC has this area outlined in a marginal outlook. The
main limiting factor at this time will be the amount of instability
that the area is able to generate. If the area is able to burn off
the fog quickly and get some clearing in the cloud cover the chances
for stronger storms will improve. The NAM is currently the most
bullish in terms of instability with MLCAPES over 1000 J/Kg and bulk
shear values nearing 40kts. Weaker forcing exists across northern MN
but a few isolated thunderstorms will not be out of the question.
Look for the shower/storms to move out of MN after midnight and
filter out of WI by Monday morning.

The upper level low continues to sit over Manitoba to start Monday
with some pulses of energy breaching our borders. Drier conditions
will be in place across northern MN after the passage of the cold
front the day prior so have toned down the previous POPs across the
region. A low pressure system moving northeast across IA into WI has
some potential to clip NW WI with another batch of rain but the
strongest moisture advection and track of the low has been pushed
slightly south with newer model runs. Overall the region will be
looking at light winds and cooler air filtering in from the north
with highs in the lower 70s.

.LONG TERM...(Monday night through Saturday)
Issued at 444 AM CDT Sun Jun 21 2020

The upper level low slowly moves eastward in the extended forecast.
A few glancing blows of shortwaves will continue to move across the
Northland through Wednesday with chances of showers and a rumble of
thunder. An upper level ridge finally ushers the influence of the
cut off low east by Thursday. This upper level ridge is very short
lived as quick moving upper level trough is projected to move into
the Northland by Friday. Thursday night low level winds shift to out
of the south bringing moist air back across the region. By Friday, a
low pressure system coming out of the Dakotas will bring a cold
front crashing into the Northland with widespread chances for rain
and storms. There is heavy model divergence going into the weekend.
Some models are suggesting a vertically stacked low remains over
northern MN while others are pushing the feature through as an upper
level trough. For now, we have kept the mention of scattered rain
showers with a few storms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 101 PM CDT Sun Jun 21 2020

Thunderstorms developing this afternoon may affect the terminals,
and have included TEMPO groups for the sites most likely to be
affected for the next few hours. Bulk of thunderstorm activity
should be ended by approximately 03z, though some showers may
linger for a few hours longer. Storms that affect the terminals
may bring a period of MVFR visiblities and ceilings, though lower
is possible. KHYR should experience a period of MVFR fog after
storms move through, but do not expect it to last all night as
drier air moves in behind the cold front that is causing the
convection this afternoon. This afternoon and early evening ahead
of the front winds will be generally be south at or less than 10
knots, then turn through southwest and west to northwest as the
front moves through, with all sites northwest by 09z this evening.
Terminals to remain VFR through the remainder of the TAF period.

&&

.MARINE...
Issued at 101 PM CDT Sun Jun 21 2020

Thunderstorms developing this afternoon ahead of a cold front may
bring locally higher winds and waves, monitor for possible weather
statements and warnings for western Lake Superior. Ahead of the
front south winds will be 5 to 10 knots. The front moves through
tonight causing winds to turn northwest to north at 5 to 10 knots.
These northwest winds to continue through Monday and Monday night.
Waves will generally remain around 2 feet or less.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  75  53  71  53 /  50  50  10  10
INL  71  48  70  51 /  20  10  10  10
BRD  77  53  72  54 /  30  30  10  10
HYR  80  58  74  52 /  60  70  10  10
ASX  80  56  72  51 /  50  60  10  10

&&

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

UPDATE...LE
SHORT TERM...Britt/JTS
LONG TERM...Britt/JTS
AVIATION...LE
MARINE...Britt/JTS

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Special Weather Statement
National Weather Service Duluth MN
234 PM CDT Sun Jun 21 2020

WIZ002-003-212000-
Bayfield-Ashland-
234 PM CDT Sun Jun 21 2020

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN BAYFIELD AND
NORTHWESTERN ASHLAND COUNTIES...

At 233 PM CDT, a strong thunderstorm was near Herbster, moving east
at 40 mph.

Wind gusts up to 30 mph, dime size hail, heavy downpours, and
frequent cloud to ground lightning can be expected with this storm.

This storm will be near...
  Bayfield Peninsula Sea Caves around 245 PM CDT.
  Sand Bay and Sand Island around 255 PM CDT.
  Bayfield and Red Cliff around 300 PM CDT.

Other locations impacted by this storm include Big Bay State Park,
Red Cliff Reservation and Apostle Islands National Lake Shore.

Seek shelter inside a sturdy building and away from windows until
this storm passes. Get off area lakes and seek shelter on shore in a
sturdy shelter or a hard topped vehicle.

LAT...LON 4675 9070 4673 9072 4677 9133 4687 9133
      4687 9128 4692 9121 4692 9109 4696 9109
      4700 9102 4705 9067 4676 9064
TIME...MOT...LOC 1933Z 262DEG 35KT 4687 9119

JDS

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