Severe Thunderstorm Warning 36, NWS Duluth, MN

Area Forecast Discussion
National Weather Service Duluth MN
656 AM CDT Fri Jun 15 2018

.SHORT TERM...(Today through Saturday)
Issued at 454 AM CDT Fri Jun 15 2018

Multiple rounds of thunderstorms through the weekend with a warm and
moist airmass across the Northland. Some storms could be strong to
severe and produce heavy rainfall, but where and when this threat is
greatest is a challenge as it will be dependent on how convection
evolves.

On the synoptic scale a mid/upper level ridge will persist across
the Upper Great Lakes region through the weekend while a longwave
trough deepens over the Pacific Northwest/Great Basin region. At
low levels southerly flow will advect a stream of warm and moist air
into a warm front boundary that will park itself in an east-east
orientation over central/northern MN into northern WI today
providing a focus for thunderstorms through today and tomorrow.
Modest instability will develop along and south of this warm front
boundary today, with anywhere from 1500 to 2500+ j/kg MLCAPE
developing by the late afternoon hours. A strong cap will likely
prevent much in the way of surface-based storm development through
the afternoon in east-central MN, but where the cap is a bit weaker
in central MN storms are expected to develop and track eastward.
There also may be a subtle mid-level shortwave trough that will
provide just enough large-scale lift to help weaken the cap combined
with surface heating. Storm activity this morning will also
influence where exactly the best environment sets up, but wherever
storms develop there will initially be a threat for large hail and
gusty winds, with storms consolidating tonight and the severe threat
diminishing.

This storm activity is expected to gradually diminish in coverage
and intensity as storms become outflow dominant and consolidate this
evening. However, as the southerly flow continues there will be
recovery of the elevated instability late tonight (after midnight),
another round of scattered to widespread strong to severe storms
will be possible. Again, this will be dependent on outflow
boundaries and resultant boundary layer conditions in place, but
confidence is high that another round of storms will develop late
tonight across northern Minnesota into northwest Wisconsin and last
into Saturday morning in some form. As the low level jet wanes
Saturday morning, activity will weaken once again resulting in a
period of lower precip chances mid-morning to early afternoon
Saturday.

Saturday will be hot and humid across the Northland as the warm
frontal boundary is expected to gradually lift northward. After
morning showers/storms, the environment will again recover thanks to
the southerly flow at low levels. A scenario similar to Friday may
occur with the cap weakening in central MN and storms firing along
the warm front from west to east. Again, primary threat early on
will be hail with a lower threat for gusty winds.

Besides the occasional hail threat, all storms will produce heavy
rainfall rates given the high precipitable water values and rich low
level moisture. Flash flood guidance is fairly high at 2-3" for a 3
hour period, and outside of very localized cases we do not
anticipate reaching that threshold with the rounds of storms today,
late tonight, or late Saturday due to their generally progressive
motions. Where the heaviest rain falls over the course of today and
tomorrow will drive where the flash flood guidance lowers and a
better risk for flash flooding arises. Most likely this will happen
with the storms expected later in the weekend as soils begin to
become saturated. But for the early part of the weekend, the primary
threat will be large hail and gusty winds.

.LONG TERM...(Saturday night through Thursday)
Issued at 454 AM CDT Fri Jun 15 2018

Upper level flow flattens Saturday night as several embedded pieces
of vorticity attempt to move over the forecast area. Several of the
models are showing convective feedback affecting these vort maxes,
which in turn affects how the thunderstorm threat evolves. This also
affects where the baroclinic zone sets up over the area, which is
the focus for the location of these storms. Model differences in the
amount and coverage of QPF are in question. Regardless, this looks
to be the best opportunity for severe storms into Sunday morning.
Plenty of instability is available, steep lapse rates, along with
PWATS approaching 2 inches for some heavy rain. The only problem
will be a capping inversion and how strong it will be. 700mb temps
will be less than 9C early in the evening, but increasing to greater
than 10C as a low level jet brings to impinge on the region. This
would lead to storms becoming elevated and introduce some question
into the severe potential. Some localized flooding may occur with
these high PWATS, by with the dry soil moisture, less than 30
percent, a lot of the rain will just be soaked into the ground. The
baroclinic zone is moving south Sunday and will still be the focus
for storms as additional vort maxes move overhead. There will be a
period of time during the day without storms, but hard to pin down
at this time. Not much change to Sunday night with additional storms
expected. A positively tilted upper trof is on the move through
Canada Monday and results in the baroclinic zone dropping out of the
area as high pressure begins to arrive with the trof. A few showers
may linger before ending in the afternoon. The surface high remains
over the area through Wednesday as the upper flow turns northwest as
the upper trof departs. The upper level ridge builds back over the
area on Thursday as more pieces of vorticity ride the ridge into the
region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 656 AM CDT Fri Jun 15 2018

First round of showers and storms were moving past the terminals
early in the forecast with VFR. This activity will diminish by mid
morning. The next round of showers and storms are forecast to
develop after 23Z. Have a VCTS or VCSH mention as when they
impact a terminal is in question. Cigs will drop into the MVFR or
IFR range nearest the stronger storms, along with gusty winds and
possibly heavy rain. This will continue through the end of the
forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  76  58  78  62 /  70  60  60  70
INL  75  57  77  58 /  40  20  50  50
BRD  84  65  79  66 /  50  60  70  80
HYR  84  64  84  68 /  70  80  50  70
ASX  81  57  81  61 /  80  70  50  80

&&

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

SHORT TERM...JJM
LONG TERM...GSF
AVIATION...GSF

Hazardous Weather Outlook
National Weather Service Duluth MN
501 AM CDT Fri Jun 15 2018

MNZ010>012-018>021-025-026-033>038-WIZ001>004-006>009-161015-
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-
501 AM CDT Fri Jun 15 2018

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

.DAY ONE...Today and Tonight

Thunderstorms will track across parts of northeast Minnesota and
northwest Wisconsin this morning, some of which could be strong to
severe producing large hail. In addition, heavy rainfall rates
will reduce visibility at times and briefly create ponding on
roads.

There will be a break in the thunderstorm activity late morning
into the afternoon today, then another round of thunderstorms is
possible late this afternoon and overnight tonight. Some storms
could be strong to severe producing large hail and gusty winds,
especially after midnight tonight. In addition, all storms will
produce heavy rainfall rates.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Several rounds of thunderstorms are anticipated Saturday and
Sunday. Strong to severe storms are possible. In addition, there
is a potential for heavy rain and some flooding, especially on
Sunday.

.SPOTTER INFORMATION STATEMENT...

Skywarn Spotters may be needed today and tonight. Reports of any
size hail, wind damage, and rainfall measurements are requested.

LSZ121-140>148-161015-
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-
501 AM CDT Fri Jun 15 2018

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

.DAY ONE...Today and Tonight

Thunderstorms are likely today and tonight. Occasional lightning,
gusty winds and heavy rain are expected.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Several rounds of thunderstorms are forecast from Saturday through
Monday. Occasional lightning, gusty winds and heavy rain are
expected through Sunday.

GSF/JJM

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

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