Severe Thunderstorm Warning 113, NWS Duluth, MN

Area Forecast Discussion
National Weather Service Duluth MN
628 AM CDT Mon Aug 5 2019

.UPDATE...
Issued at 628 AM CDT Mon Aug 5 2019

Please see the 12Z Aviation discussion below.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 407 AM CDT Mon Aug 5 2019

Thunderstorm complex over North Dakota and northwest Minnesota is
expected to progress east-southeastward through this morning. The
eastern periphery of the thunderstorm complex will likely move
into Cass, Crow Wing, Aitkin, and Pine counties between 6 and 9
AM. A cold front will push southeastward along with the storms
which will continue to provide low-level convergence to sustain
storms. The airmass over our Minnesota zones remains unstable, but
capped as of 4 AM. The cap is expected to erode ahead of the
complex by mid-morning allowing storms to root in the boundary
layer as they move out of the forecast area by early afternoon.
Additional storm development is expected along the cold front as
it moves through northwest Wisconsin this afternoon. Some of the
storms may be strong to severe with large hail and damaging winds
possible. MLCAPE values on the order of 1000-1500 J/kg is forecast
along with 0-6 km bulk shear of 35 to 40 knots. The storms will
move out of the area by early this evening as high pressure moves
into the Northland. Drier air will filter into the region for
Tuesday. Temperatures won’t be much cooler, but the drier air
will make conditions more comfortable.

.LONG TERM...(Tuesday night through Sunday)
Issued at 407 AM CDT Mon Aug 5 2019

Showers and thunderstorms expected Tuesday night through
Wednesday as a cold front slides through. After the front slides
through expect dry and quiet weather with near normal temperatures
as high pressure takes control.

A cutoff low will slowly rotate southeastward from northern
Manitoba Tuesday night into Hudson Bay and northern Ontario by
Wednesday night. At the surface a cold front will slide
southeastward through northern Minnesota and northern Wisconsin.
This will bring showers and thunderstorms to most of the region.
There is an opportunity late in the morning and during the
afternoon for some stronger thunderstorms across much of northwest
Wisconsin. Along and just behind the cold front 0-6 km bulk shear
values will be around 40 to 45 knots. Just ahead of the front
instability values vary depending on model output. The GFS seems
more reasonable at this point in time with values ranging from a
few hundred to around 2000 J/kg of CAPE, while the latest NAM is
much more bullish with values up to 4000 J/kg. The 12Z NAM is more
in line with the latest GFS, which seems more reasonable. The big
question at this point in time is if the shear couples with the
instability, which seem a bit offset at this point. If it is able
to do so then some severe storms are possible. Main threats for
storms would be damaging wind gusts and large hail. This matches
up well with the latest SPC Day 3 Outlook. Behind the front winds
aloft will shift to the northwest and advect cooler air into the
region. High temperatures will be in the 70s.

High pressure will build into Northern Plains and central Canada
late on Wednesday into early Thursday. The cutoff low will remain
generally in the same location as the previous day. Flow will
remain northwesterly advecting cooler air into the region. With
the high nudging in skies will be partly cloudy to mostly clear.
Lows range from the mid 40s to the mid 50s. The high will build
into the Upper Midwest on Thursday which will keep the weather dry
and quiet. Cool northwesterly flow will continue. High pressure
will remain in control on Friday as it builds into the Mid
Mississippi River Valley. Flow aloft will gradually switch from a
cool northwesterly direction to a westerly direction. This will
begin advecting warmer air into the region. Temperatures will be
slightly warmer on Friday with highs in the mid to upper 70s.

Confidence in the forecast after Friday decreases as the latest
guidance is split on the intensity of the next wave moving in from
the northwest. The latest ECMWF/GEM depict a much stronger
shortwave when compared to the previous runs of the ECWMF/GEM and
the latest and previous GFS. If things trend toward the latest
ECWMF/GEM then Saturday will be much wetter than Sunday, whereas
previous runs of these models and current and past GFS show a
relatively dry forecast. Have leaned on majority of runs showing a
drier forecast and is reflected in the forecast. Sunday at this
point in time has a better opportunity for showers and storms, but
again being a week out the confidence in the evolution of things
is low. Will need to monitor things as the week progresses.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 628 AM CDT Mon Aug 5 2019

Anticipating MVFR/IFR conditions this morning as fog lifts. Expect
MVFR/IFR to continue mainly across HIB, BRD, DLH this morning as
a mesoscale convective system moves through bringing showers and
thunderstorms. Uncertain how low visiblities will get at this
time, but have honed in on thunderstorm timing based on current
radar trends and the HRRR guidance. Thunderstorms will develop to
the north of the MCS this afternoon over northwest Wisconsin per
HREF guidance. This will bring MVFR and potential IFR conditions
at HYR this afternoon. Behind the thunderstorms expect conditions
to improve to VFR with winds shifting to a northwesterly direction
as the cold front slides through.

Winds will become light and variable as skies clear and high
pressure builds in tonight. Expect some fog development with
recent precipitation and light winds. Only mention at HYR at this
point in time, but will likely need at other terminals in later
TAF updates.

&&

.MARINE...
Issued at 407 AM CDT Mon Aug 5 2019

Generally quiet in the marine with strengthening southwesterly
flow on Monday. Winds will be 10-15 knots with gusts around 15
knots during the afternoon. The main concern will be thunderstorm
activity during the morning and through much of the afternoon as a
cold front slides through. A few strong to severe storms are
possible. The main threats with any storms would be strong winds,
hail and cloud to water lightning.

Winds will gradually shift to the northwest behind the front
tonight into early Tuesday. On Tuesday a weak high will build in
and shift winds again to a southerly direction. Wind speeds will
be at 10 knots or less with dry weather.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  80  57  82  59 /  50  10  10  20
INL  81  54  82  53 /  20   0  30  30
BRD  81  59  84  61 /  90  10  10  30
HYR  80  56  82  60 /  60  20  10  20
ASX  82  58  83  61 /  40  10   0  20

&&

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

UPDATE...WL
SHORT TERM...Huyck
LONG TERM...WL
AVIATION...WL
MARINE...WL

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