280
FXUS63 KDLH 181734
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1234 PM CDT Tue Jun 18 2024

.KEY MESSAGES...

- A few severe storms will be possible early this morning with
  damaging wind gusts to around 60 mph being the primary threat
  (20-30%) with the line approaching from the west. Elevated
  storms ahead of the line pose a threat for large hail
  (10-20%).

- Another round of severe storms will be possible this afternoon
  as a cold front moves through the region. The main threats
  will be damaging wind gusts to 60 mph and large hail (20-40%),
  but an isolated embedded tornado or two (2%) cannot be ruled
  out.

- Overall flash flood threat continues to diminish with lower
  QPF expected across the region. However, isolated pockets of
  1-3 inches are still forecast across parts of Koochiching and
  northern St. Louis counties. The Flash Flood Watch has been
  trimmed to the north where the heaviest rainfall is expected.

- After a short break, the pattern remains active with
  additional chances for rain and storms into the weekend along
  with a heavy rainfall threat.

&&

.DISCUSSION...
Issued at 459 AM CDT Tue Jun 18 2024

Low pressure was located over central South Dakota early this
morning with a warm front stretching into southern Minnesota and
central Wisconsin. Another area of low pressure was analyzed
over eastern North Dakota with a stationary boundary stretching
into northwestern Minnesota and northwestern Ontario. Showers
and thunderstorms were moving across northeastern Minnesota in
association with the warm front. These storms carry a risk of
large hail to the size of half dollars along with heavy
rainfall. A line of storms across northwestern Minnesota ahead
of stationary boundary has been producing severe wind gusts
across eastern South Dakota and northwestern Minnesota. As this
line continues to push east early this morning, the threat for
damaging winds will continue. A Severe Thunderstorm Watch has
been issued for much of northeastern Minnesota with the
exception of the Arrowhead through 9AM this morning.

As the day progresses, the stationary boundary is expected to
very slowly shift eastward. Additional waves of showers and
thunderstorms are expected to develop along and ahead of this
front across north-central and northeastern Minnesota. A very
warm and moist airmass will move into the region ahead of the
stationary/cold front characterized by dewpoints in the 60s and
lower 70s and highs in the 80s. This will lead to building
instability of 2000-3000 J/kg in areas east of the existing
showers and storms. Effective shear remains around 35-40 knots
with nearly unidirectional shear aloft favoring a linear storm
mode through the event. CAMs keep convection over Cass, Itasca,
Koochiching and northern St. Louis counties, which may limit the
severe potential in those areas. In any case, damaging wind
gusts to around 60 mph (30-40%) and hail to around 1" (20-30%)
look to be the primary threats in any storms, although the
linear nature of the storms may limit the hail potential. A few
embedded tornadoes cannot be ruled out with SRH approaching 300
m2/s2 and along with decent speed shear in the lower levels.
Heading into the evening hours, the front looks to be more
progressive and will shift the showers and storms into
northwestern Wisconsin with an overall diminishing trend by mid
to late evening. A few showers may linger behind the front
overnight, but any additional rainfall will be light.

Speaking of rainfall, overall QPF for today continues to trend
lower across the region. Most of the region will see around an
inch or less of rainfall today with isolated higher pockets in
stronger areas of convection. PWATs remain at the top of
climatology for the day, so we may still overachieve in the
rainfall department in spots. Heavier rainfall amounts of 1-2
inches plus is expected across parts of Koochiching and
northern St. Louis County. This is the area that CAMs keep heavy
rainfall in place through much of the day. This area will see
the highest risk for any flash flooding today. With the lower
QPF amounts elsewhere, have trimmed back the Flash Flood Watch
to Koochiching, northern and central St. Louis, Itasca and
northern Cass counties. Advisory level flooding will still be
possible elsewhere given saturated ground and already high
rivers and streams, but the overall flash flood threat has
diminished.

With highs in the 80s today across northwest Wisconsin and
dewpoints in the 70s, heat indicies will be in the 90s for most
of northwest Wisconsin. While this is not advisory level heat
indicies, it will be very warm and muggy and uncomfortable for
many.

High pressure will then move through the Upper Midwest for
Wednesday into Thursday bringing dry conditions with
temperatures in the 70s. The pattern then remains active with
southwest flow bringing another large system through the region
starting Thursday and Friday with a warm front before a stronger
low moves through for Saturday into Sunday. Ample moisture will
move into the region from the Gulf of Mexico with PWATs rising
to near the top of climatology once again. Instability continues
to look anemic during much of this time period with the heavy
rainfall threat being more of a concern. NBM probabilities have
not changed much with chances of an inch or more remaining
around 50 to 80% and chances for 2 inches or more at 30 to 50
percent. Given the rainfall currently occurring, many areas will
be primed to be mainly runoff with saturated ground and already
high rivers and streams.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1230 PM CDT Tue Jun 18 2024

A period of severe thunderstorms is expected across most of
north-central and northeast Minnesota from 20Z Tuesday to 02Z
Wednesday and produces hail to the size of a ping pong ball,
heavy rainfall producing visibility down to 1SM and erratic wind
gusts to 35 knots. The line of strong to severe thunderstorms
moves into northwest Wisconsin after 00Z into 02Z, but weakens
after 03Z as it trecks eastward. IFR ceilings are very likely
ovenright and into early Wednesday morning through 12Z.
Northwest winds and clearing skies accompany the post-cold front
environment tomorrow 12-18Z.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 459 AM CDT Tue Jun 18 2024

Periods of showers and storms are expected over western Lake
Superior today into this evening. Strong to severe storms will
be possible this afternoon and evening with wind gusts to 50
knots being possible along with hail to around 1 inch in
diameter. A cold front will work across the western part of the
lake late this afternoon and evening with storms expected to end
following the passage of the front.

Winds outside of any storms today will be southerly at 5 to 15
knots with gusts to 20 to 30 knots, highest near the Twin Ports.
These winds will also generate waves of 2 to 5 feet along the
North Shore. Small Craft Advisories remain in effect for all of
the nearshore waters for today into tonight. High pressure moves
in late tonight and remains in place for Wednesday and Wednesday
light leading to winds under 15 knots.

For the open water discussion, refer to the NWS Marquette Area
Forecast Discussion at weather.gov/mqt.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch through Wednesday morning for MNZ010>012-018-019-
     025-026.
WI...None.
MARINE...Small Craft Advisory until 1 AM CDT Wednesday for LSZ121-
     144>148-150.
     Small Craft Advisory from 9 PM this evening to 1 AM CDT
     Wednesday for LSZ140>143.

&&

$$

DISCUSSION...BJH
AVIATION...NLy
MARINE...BJH