Special Marine Warning 21, NWS Duluth, MN

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

.UPDATE...
Issued at 633 PM CDT Thu Sep 14 2017

Strong to severe thunderstorms continued across portions of
northeast Minnesota with additional showers and storms continuing
to form west to the North Dakota border. Strong low level FGEN is
present and will be through much of tonight and a low level jet
will be strengthening this evening but should then shift east more
into northern Wisconsin later tonight. We think showers and
storms will continue through much of tonight, especially over
northern Minnesota. There will be a threat for very heavy rain. A
report just west of Crane Lake was around 2.5 inches of rain as of
530 pm. We will be issuing a Flash Flood Watch for much of far
north to northeast Minnesota through 11Z to account for the
possible heavy rainfall.

&&

.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 00Z TAFS through 00Z Friday evening)
Issued at 633 PM CDT Thu Sep 14 2017

A stalled frontal boundary and low level FGEN has led to showers
and strong to severe thunderstorms over northern Minnesota this
afternoon and early evening. The showers/storms will continue
overnight as the strong FGEN forcing is forecast through the
night. Ceilings will lower for most areas overnight along with fog
developing. IFR/MVFR conditions will expand, especially over
northern Minnesota and they will continue into Friday. An area of
low pressure will then move toward the region on Friday producing
more showers/storms and IFR/MVFR conditions.

&&

.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.
&&

UPDATE...Melde
SHORT TERM...JTS
LONG TERM...Grochocinski
AVIATION...Melde

Hazardous Weather Outlook
National Weather Service Duluth MN
728 PM CDT Thu Sep 14 2017

MNZ010>012-018>021-025-026-033>038-WIZ001>004-006>009-151030-
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-
728 PM CDT Thu Sep 14 2017

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

.DAY ONE...Tonight

Thunderstorms will continue overnight. A few storms may be strong
to severe over portions of northern Minnesota. Hail and gusty
winds are possible with these stronger storms. Heavy rain will
also be possible as showers and storms continue to form and move
across the same areas, possibly leading to flash flooding. A Flash
Flood Watch is in effect through 6 am.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Strong northeast flow over western Lake Superior, down to the
Twin Ports area, on Friday will likely cause a high risk of
dangerous rip currents along Duluth's Park Point Beach and
Superior's Wisconsin Point Beach through the day.

Thunderstorms are possible across northeast Minnesota and
northwest Wisconsin Friday night through Saturday night. Some
storms Saturday afternoon and evening could be strong.

Periods of thunderstorms are possible across northeast Minnesota
and northwest Wisconsin Tuesday night through Wednesday.

.SPOTTER INFORMATION STATEMENT...

Skywarn Spotters may be needed tonight.

LSZ121-140>148-151030-
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-
728 PM CDT Thu Sep 14 2017

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

.DAY ONE...Tonight

Thunderstorms are possible tonight. Some storms may contain hail
and gusty winds.

Northeast winds will create hazardous conditions for small craft
over far western Lake Superior tonight.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

Northeast winds will continue to increase over western Lake
Superior late tonight and Friday. The wind and resulting waves
will likely result in widespread hazardous conditions for small
craft across western Lake Superior, especially along the South
Shore and Twin Ports area, until the winds and waves sufficiently
subside later Friday night.

Periods of thunderstorms are possible over western Lake Superior
Friday afternoon through Saturday night. Additional periods of
storms are possible Tuesday night and Wednesday.

Melde

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

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