Severe Thunderstorm Warning 117, NWS Duluth, MN

Area Forecast Discussion
National Weather Service Duluth MN
314 PM CDT Thu Sep 14 2017

.SHORT TERM...(This evening through Friday)
Issued at 311 PM CDT Thu Sep 14 2017

Increasing chances of showers and thunderstorms will occur this
evening as a more active weather pattern sets up across the region.
A mid-level shortwave trough, along with enhanced 850-700 mb layer
frontogenetical forcing, will act as the mechanism for these showers
and storms. The environment should be capped in some locations,
given values of MLCIN in the 50 to 150 J/kg range. However,
there's plenty of elevated instability, with MUCAPE values from
the 14.12z GFS/CMC/NAM models between 1000 to 2000 J/kg, so if
storms can break through the capping inversion, there is plenty of
instability for them to tap into. The HRRR model is indicating
some stronger convective cells out ahead of the leading wave, so
that will need to be watched from 23z this afternoon onward. So
far this afternoon, we've issued a few SPSs due to a single strong
thunderstorm that developed over northwest Minnesota and
translated east-northeastward over Koochiching county. However, it
appears to be struggling to sustain its updraft despite the
amount of instability in the region. Heavy rainfall is possible
with some of these storms, given Pwat values between 1.3 and 1.6"
tonight.

Along with the chances of showers and storms tonight, areas of fog
is expected to develop due to on-shore flow tonight, along with
low condensation pressure deficits and light winds. Fog is
expected to begin along Lake Superior, and build further inland as
the night goes on. Most of the heavy rainfall is expected over the
Iron Range eastward into the Minnesota Arrowhead regions. Chances
of thunderstorms should decrease after midnight due to the loss
of favorable instability. The respite from storms will be short-
lived as another round of showers and storms are expected again
Friday as another shortwave trough moves into the region. The
convective-allowing models are struggling to resolve the activity
for Friday, as the NAMNest model is more active than the WRF
NMM/ARW models, which are going drier. While uncertainty does
exist, the synoptic models are showing decent agreement on
precipitation chances around the forecast area. Chances of
thunderstorms will increase Friday afternoon as better
destabilization builds. A strong baroclinic zone will remain over
the region given more southerly winds over northwest Wisconsin and
more northerly winds along the International Border. High
temperatures Friday will range from the upper 50s and lower 60s
north to the middle to upper 70s south, with some lower 80s also
possible.

.LONG TERM...(Friday night through Thursday)
Issued at 254 PM CDT Thu Sep 14 2017

The Northland will begin the period with cool, easterly low level
flow, and warm and humid southwest flow aloft. An area of low
pressure will be in the Central Plains Friday evening. Much cooler
wrap around air will be in western North Dakota and in Canada,
waiting to swing into the Northland once the Central Plains low
moves through the region. Passing shortwaves and the strong nocturnal
low-level jet could trigger showers and thunderstorms across the
Northland Friday night, while the Central Plains low lifts to
northern MN.

The low will continue to move through northern MN Saturday, lifting
into Ontario Saturday night. It's cold front will slowly work its
way eastward across northern MN Saturday, then rapidly swing through
the Northland Saturday night when a deep upper-level low lifts into
the Northern Plains and south-central Canada. The Northland could
get showers and thunderstorms Saturday and Saturday night. A few
storms could be strong, capable of small hail and heavy rain.

People across the Northland may wake up to what feels like fall on
Sunday. Much cooler air will move into the region amid the westerly
flow in the wake of the cold front. Expect a cool and breezy day.
Concerned models may be too warm, but stuck with model consensus for
now. We might cool the forecast with time. Cloud cover will play a
part. Most models think it will be mostly sunny, but the residual
moisture from the previous day, combined with the very cold air,
might trigger broken cumulus in the afternoon, which would limit
heating. The forecast for now is for highs in the upper 50s to lower
60s.

Southerly flow will redevelop Monday and bring back warmer air into
the region into the middle of the week. The moisture return will
also increase the chances of showers and storms. The GFS has much
more robust precipitation than the European. The best chances will
likely be when the cold front swings through during the middle of
the week, but the GFS has this occurring significantly sooner than
the European and Canadian.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1237 PM CDT Thu Sep 14 2017

A warm front will remain draped from southeast to northeast across
the northland through the TAF time range. This front will serve as
the focus for showers and a few thunderstorms through much of the
TAF period, especially in the 20z through 09z time range. Have
included shower and thunderstorm chances mainly for KINL and KHIB,
but KDLH may only see a few isolated showers, with no convection
expected near KBRD and KHYR. High levels of low level moisture to
remain southeast of the front, and expect redevelopment of fog and
stratus after 01z for KDLH and KHIB, with some MVFR fog for KBRD.
KDLH to be most affected with several hours of LIFR conditions
again in the 09z-14z time range.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  59  67  57  72 /  30  50  60  40
INL  53  59  53  63 /  60  80  80  50
BRD  61  75  62  69 /  20  60  60  50
HYR  63  80  63  79 /  10  30  40  30
ASX  59  74  60  78 /  20  30  40  40

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement until 8 PM CDT this evening for WIZ001.

MN...Beach Hazards Statement until 8 PM CDT this evening for MNZ037.

LS...None.
&&

SHORT TERM...JTS
LONG TERM...Grochocinski
AVIATION...LE

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Special Weather Statement
National Weather Service Duluth MN
202 PM CDT THU SEP 14 2017

MNZ010-141930-
Koochiching-
202 PM CDT THU SEP 14 2017

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN KOOCHICHING
COUNTY...

At 202 PM CDT, a strong thunderstorm was over southeastern Upper Red
Lake, moving east at 30 mph.

Wind gusts up to 40 mph, nickel-size hail, and frequent cloud to
ground lightning can be expected with this storm.

this storm will remain over mainly rural areas of northwestern
Koochiching County.

Seek shelter inside a sturdy building and away from windows until
this storm passes.

LAT...LON 4857 9406 4805 9403 4803 9443 4848 9443
TIME...MOT...LOC 1902Z 264DEG 24KT 4810 9469

G2

Special Weather Statement
National Weather Service Duluth MN
229 PM CDT THU SEP 14 2017

MNZ010-142000-
Koochiching-
229 PM CDT THU SEP 14 2017

...A STRONG THUNDERSTORM WILL AFFECT SOUTHWESTERN KOOCHICHING
COUNTY...

At 228 PM CDT, a strong thunderstorm was near Waskish, moving east at
35 mph.

Wind gusts up to 40 mph, nickel-size hail, heavy downpours, and
frequent cloud to ground lightning can be expected with this storm.

This storm will be near...
  Gemmell around 250 PM CDT.

Seek shelter inside a sturdy building and away from windows until
this storm passes.

LAT...LON 4827 9442 4829 9403 4794 9404 4800 9442
      4802 9442 4802 9443 4803 9443
TIME...MOT...LOC 1928Z 273DEG 30KT 4811 9440

JTS

Special Weather Statement
National Weather Service Duluth MN
305 PM CDT Thu Sep 14 2017

MNZ010-011-018-142115-
Koochiching-North St. Louis-North Itasca-
Including the cities of International Falls, Ely, and Bigfork
305 PM CDT Thu Sep 14 2017

...THUNDERSTORMS EXPANDING IN COVERAGE ACROSS NORTH CENTRAL
MINNESOTA LATE THIS AFTERNOON...

Between 3 and 4 PM CDT, thunderstorms will continue to expand in
coverage across much of north central Minnesota, affecting most of
Koochiching, northern Itasca, and northern St. Louis Counties.
Storms should begin affecting Voyageurs National Park, and the
western sections of the Boundary Waters Canoe Area Wilderness
between 330 and 4 PM.

Heavy downpours and frequent cloud to ground lightning can be
expected in these areas. In addition, a few of the storms could
reach strong or marginally severe levels, producing nickel to
quarter size hail, and wind gusts above 40 mph.

Anyone with outdoor plans in these areas for the remainder of this
afternoon and evening should have a plan to seek shelter indoors
and away from lakes and trees when thunderstorms approach.