Severe Thunderstorm Warning 19, NWS Duluth, MN

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
713 AM CDT Sun Jun 11 2017

.UPDATE...
Issued at 706 AM CDT Sun Jun 11 2017

Current radar trends this morning showing a complex of severe
thunderstorms moving eastward across southwest Minnesota, which
may scrape across our southern periphery of counties (Pine to
Price county). There have already been reports of penny size hail
and wind gusts between 60 to 70 mph near Granite Falls. The HRRR
model is showing thunderstorm complex, which has taken on a bowing
convective mode, to ascend east-northeast, and impact the
aforementioned counties. Thus, a Severe Thunderstorm Watch has
been issued for these counties, in effect through noon today. Main
threats will be damaging winds and large hail.

&&

.SHORT TERM...(Today through Monday)
Issued at 357 AM CDT Sun Jun 11 2017

A quiet early morning will continue for at least a few more hours
before more potential for severe weather develops later this morning
and into the afternoon. The current radar trends show some light
returns draped over northern Cass/southern Itasca counties at
4:00 AM CDT this morning. Not thinking that much of this is
hitting the ground as there is plenty of dry air near the sfc, and
cloud bases are around roughly 10,000 ft. However, some more
robust showers are showing up further upstream, which do appear to
be reaching the ground as per automated observing sites. The
bigger near-term concern will be for the development of an MCS
that may impact the southern portions of our forecast area later
this morning. The latest meso-models indicate an MCS with parallel
stratiform rainfall to the north of the strongest segment of the
system. There could be some large hail and damaging winds with the
main portion of the system as 0-6 km deep-layer shear should
range between 55 to 65 kts, and DCAPE values increase to 500-1000
J/kg. This MCS should ride along a sfc warm front boundary, which
will continue to lift northward and be the focus of convection
throughout the day. This entire system should have plenty of mid-
and upper-level support as the Northland should be underneath the
right-entrance region of the upper-level 140+ kt jet streak,
placing the region over an area of upper-level divergence. A
compact mid-level shortwave will also translate across the south
and eastern portions of the forecast area, which will bring plenty
of isentropic lift with it.

There is an enhanced risk of severe weather today south of a Pine
City to Hayward to Lac Du Flambeau line, along with a slight risk
extending about one county north from the enhanced risk. Given
the increase in MLCAPE along the warm front, continued strong deep
layer shear, and the development of a low-level jet that will
impinging on this environment, severe weather risk will increase
this afternoon after the initial MCS moves through. All modes of
severe weather are possible today, with large hail and damaging
winds as the main threat, with a lower risk of tornadoes possible,
especially over northwest Wisconsin where the baroclinic zone
appears to become more stationary later this afternoon and evening.
Another big threat will be heavy rainfall that could lead to
flash flooding. Model ensembles, including the NAEFS and ECMWF
ensembles, indicate anomalously high Pwat values approaching ~2
inches, which is well above climatological averages. These values
appear to be over the 99th percentile, so plenty of moisture will
be available to precipitate out. We considered issuing a Flash
Flood Watch for a good portion of northwest Wisconsin, but there
is still some uncertain with the storm motion. Corfidi forward
propagation vectors lead me to believe that some training
convection will be possible, which would exacerbate the flooding
concerns for this afternoon and evening.

Beyond tonight into Monday morning, things should quiet down
somewhat across much of the Northland, with some lingering chances
of showers with some thunderstorms possible over our extreme
southern areas as the baroclinic zone lingers over this area.
There could be another round of strong to severe thunderstorms
over the the southern portions of the Northland, but at this
point, the likelihood for severe storms will be on the low side,
as the deeper lift doesn't appear as robust as it will be today.

.LONG TERM...(Monday night through Saturday)
Issued at 357 AM CDT Sun Jun 11 2017

Numerous rounds of showers and thunderstorms early to mid week, then
a break in the precipitation late-week. Precipitation chances return
for the weekend with a chance for showers and a few storms Saturday.
Temperatures above normal through much of the long term period, with
the notable exception of cooler temperatures near Lake Superior
Tuesday due to strong easterly winds. Guidance diverges for weekend
scenarios with highs on Saturday at Duluth ranging from the 50s
(from guidance that depicts easterly low level winds) to upper 70s.

On the synoptic scale the driver for the weather this week will be
an upper low traversing from west to east across North America. On
Monday the upper low will be located over Nevada, lifting northeast
towards the northern High Plains by Tuesday. On Wednesday the upper
low moves north into southern Saskatchewan and Manitoba, then drifts
eastward into northwest Ontario Thursday into Friday. A resultant
surface low will develop over the central high plains Monday.
lifting north into the northern Plains Tuesday, then into Canada as
the low becomes vertically stacked mid-week. Ahead of this low,
southerly flow across the Great Plains and Mississippi River Valley
will lead to warm and moist air to advect northward, much of the
convection late Monday into Tuesday will be driven by the warm
sector of the low as this warm and moist airmass advects into the
Upper Midwest. The cold front associated with the main low will move
east across the region late Wednesday, with large-scale subsidence
building in Thursday into Friday a a mid-level shortwave ridge
builds in from the west and cooler air advects in from the northwest
at low levels.

Monday night into Tuesday the warm front lifts north across northern
Minnesota and northwest Wisconsin with scattered to widespread
showers and storms possible along the front. Elevated instability
will be in excess of 2000 j/kg behind the front, driven by very
steep mid-level lapse rates. Combined with deep layer shear on the
order of 30 to 45 knots, there will be at least a conditional risk
for organized severe thunderstorms. The limiting factor Tuesday will
be strong easterly winds ahead of and along the front which will
result in Lake Superior influencing the lower levels of the
atmosphere in northern Minnesota on Tuesday. Still, even if surface-
based convection is limited to areas of north-central Minnesota due
to the cooler surface temperatures near Lake Superior, the north-
northeast storm motion would likely advect strong to severe storms
into northeast Minnesota come Tuesday afternoon/evening. The Storm
Prediction Center has a marginal to slight risk for severe storms
in north-central to northeast Minnesota. The main threats with
storms Tuesday into Tuesday night will be large hail and damaging
winds, with low-level shear favorable for tornadoes where surface-
based storms can develop - mainly in north-central Minnesota such as
the Brainerd Lakes area.

On Wednesday widespread showers and thunderstorms will develop ahead
of the approaching cold front, with a few strong to severe storms
possible.

Skies clear out behind the cold front Wednesday night into Thursday,
but with the upper low slow to exit southern Manitoba on Thursday,
some mid to high level clouds will impact far northern Minnesota
Thursday into Friday. In addition, while widespread precipitation is
not anticipated, the cooler temperatures aloft may lead to some
stratocu and a few showers both Thursday and Friday in the wake of
the front.

There remains a significant amount of uncertainty as to the large-
scale pattern for the weekend, but the general model consensus is a
pattern that would favor chances for showers and storms Saturday
with temperatures near normal for the weekend. Despite the
uncertainty, severe storms appear unlikely in most of the
deterministic and ensemble member solutions.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 645 AM CDT Sun Jun 11 2017

VFR conditions will prevail at all TAF sites for most of today
with the exception of thunderstorms lowering ceilings to MVFR at
HYR mid morning. This afternoon into this evening MVFR ceilings
and fog is expected to develop at all sites with the exception of
INL where ceilings at expected to remain VFR. East to southeast
winds today remaining light at around 10 knots or less outside of
thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  73  53  80  54 /  60  30   0  30
INL  78  54  77  52 /  50  10   0   0
BRD  73  55  82  60 /  80  10  10  30
HYR  81  59  84  61 /  80  80  10  40
ASX  78  57  81  53 /  70  60   0  30

&&

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

UPDATE...JTS
SHORT TERM...JTS
LONG TERM...JJM
AVIATION...JJM

Hazardous Weather Outlook
National Weather Service Duluth MN
656 AM CDT Sun Jun 11 2017

MNZ010>012-018>021-025-026-033>038-WIZ001>004-006>009-120815-
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-
656 AM CDT Sun Jun 11 2017

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

.DAY ONE...Today and Tonight

A few rounds of showers and thunderstorms, with some strong to
severe, are expected today through the evening hours. A Severe
Thunderstorm Watch has been issued for Pine county in northeast
Minnesota, and Burnett, Washburn, Sawyer, and Price counties in
northwest Wisconsin. The watch will continue through noon today.

There is an enhanced risk of severe weather south of a Pine City
to Hayward to Lac Du Flambeau line, and a slight risk for adjacent
areas north of the enhanced risk, with the main threats being
large hail and damaging winds, along with a smaller risk of
tornadoes, and frequent lightning. Heavy rainfall will be possible
over northwest Wisconsin later this afternoon and evening, which
may lead to flash flooding.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Another round of showers and thunderstorms will be possible for
Monday, especially for southern portions of the Northland. Some
storms could be strong to severe, with large hail and damaging
winds the main threats.

Thunderstorms are expected Tuesday through Wednesday across much
of the Northland. Strong to severe storms will be possible in
north- central Minnesota Tuesday afternoon and evening, with large
hail and damaging winds expected from the strongest storms.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters may be needed today to call in reports of hail of
any size, damaging winds, tornadoes, and flash flooding.

LSZ121-140>148-120815-
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-
656 AM CDT Sun Jun 11 2017

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

.DAY ONE...Today and Tonight

A few rounds of thunderstorms are expected today and tonight
across western Lake Superior, especially along the south shore. A
few storms could be strong to severe this afternoon and evening.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Thunderstorms are possible across western Lake Superior Tuesday
night into Wednesday. These storms are not expected to be severe.

Increasing easterly winds Monday night through Wednesday will
lead to building waves across western Lake Superior, which will
result in hazardous conditions for small craft. A Small Craft
Advisory will be needed.

JTS/JJM

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

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