207
FXUS63 KDLH 181553
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1053 AM CDT Sat May 18 2024

.UPDATE...
Issued at 1053 AM CDT Sat May 18 2024

We are continuing to monitor the potential for a few strong to
severe thunderstorms this afternoon. The cold front is easily
visible on satellite with some stratocumulus moving east through
northern Minnesota. The wind shift and temperature drop behind
the front suggests it is currently located around or just west
of Brainerd and stretching north towards Lake of the Woods.

A narrow corridor of SBCAPE between 500 and 1000 J/kg is
developing over central Minnesota, stretching across the entire
state. Skies are clear out ahead of this, so we expect the air
to become more unstable ahead of the front. The latest CAMs
suggest that storm initiation could start as early as ~2 PM, but
more likely around 3 PM in the Arrowhead first, then perhaps
delayed by an hour in northwest Wisconsin. The best instability
and steepest mid-level lapse rates will be displaced from the
highest 0-6 km shear around 50-60 kt to the west (~30-40 kt
around storm initiation), so widespread severe weather isn`t
expected, but certainly isolated to scattered strong to severe
storms.

Initial storm development is likely to be discrete, and thus
hail will be the main threat initially. It wouldn`t be
surprising to have a storm or two capable of producing hail up
to 1.5" in diameter. There is a notable amount of DCAPE up to
1000 J/kg, so strong winds to around 60 mph (can`t completely
rule out 70 mph, though that`s less likely) remain a possibility
as well. Storms are expected to move east/northeast pretty
swiftly, giving a 4-5 hour maximum window for these strong to
severe storms from about 2-7 PM. After the storms move east,
stable air behind the front is expected to end the threat for
storms for the rest of tonight.

&&

.KEY MESSAGES...

- Marginal Risk for severe storms this afternoon and evening
  with large hail up to quarter size and gusty winds being the
  biggest concern

- Short dry spell Saturday night and Sunday morning before our
  active weather pattern returns next week with multiple periods
  of rain through the week.

&&

.DISCUSSION...
Issued at 521 AM CDT Sat May 18 2024

A round of scattered showers and isolated thunderstorms is
moving through the area this morning as a low pressure system
and cold front advance through the area. An upper level
shortwave will also move across the area this afternoon, and as
it interacts with the front, we should have a decent trigger for
thunderstorms. How strong the storms get depends on just how
much instability we can build ahead of the front. Deep layer
shear will be sufficient for some isolated strong to severe
storms, though I do not expect this to be a widespread threat.
This will also be confined to along and east of the cold front,
depending on where it is located by early afternoon. It will be
warm and humid ahead of the front, with highs getting into the
low 80s for northwest Wisconsin and 70s for northern Minnesota.
These temperatures will be well above normal, but nowhere close
to record highs, which are around 90.

Behind the cold front tonight and Sunday morning I expect a
period of quieter weather with cooler temperatures, with highs
in the 70s. A ridge of high pressure will slide across the area,
producing lighter winds as well.

Our next chance of precipitation moves in Sunday afternoon and
night as yet another shortwave and surface low system moves
towards the area, and then across the area on Monday, bringing a
higher potential (60% or more) for more than a quarter inch of
rainfall, especially over northwest Wisconsin, closer to the
surface low track. Much of the area will get a break in
precipitation Monday night.

Another round of precipitation as a fairly potent shortwave and
a strong surface low moves from the KS/NE high plains north-
northeast across IA and then across WI Tuesday through
Wednesday. For now there is fairly decent ensemble agreement on
this general pattern, and it appears most members bring the
surface low to the southeast of the forecast area. This should
bring mainly rain/rain showers and less thunder, but the farther
north the track, the more potential we will have for
thunderstorms and perhaps even severe weather. The more
southerly track for now favors cooler temperatures for Tuesday
and Wednesday as well. Lingering smaller precipitation chances
linger Thursday through Saturday along with cooler temperatures
in the wake of the stronger mid week system.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 623 AM CDT Sat May 18 2024

Scattered showers and a few storms are moving across the
terminals this morning. They should weaken through the morning,
but until then could bring a brief period of MVFR ceilings and
visibilities. Am not confident enough in timing to include in
each terminal, but have put VFR VCTS groups for now. Strong
southerly winds aloft will produce LLWS this morning,
dissipating by 15z. New showers and storm development is
expected for the Arrowhead and northwest Wisconsin after 16z,
then quickly moving off to the east by 21z. After 21z, all
terminals should be VFR, with winds decreasing to less than
10kts by 03z.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 521 AM CDT Sat May 18 2024

Northeast winds today will switch around th the west-southwest
and increase in the wake of a cold front. These stronger winds
are expected to cause hazardous conditions for small craft from
late this morning through the afternoon and evening before
diminishing again overnight tonight. The strongest winds are
expected along the South Shore and around the Twin Ports. The
southwest winds continue on Sunday, and we may get a period of
hazardous conditions once again Sunday afternoon, but this time
along the North Shore north of Grand Marais. Winds begin to
switch around to the southeast and then east Sunday night, and
then northeast by Monday morning. For now it does not appear
winds will be strong enough for hazardous conditions on Monday.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
MARINE...Small Craft Advisory until 10 PM CDT this evening for LSZ121-
     148.
     Small Craft Advisory from 4 PM this afternoon to 10 PM CDT
     this evening for LSZ144>147-150.

&&

$$

UPDATE...JDS
DISCUSSION...LE
AVIATION...LE
MARINE...LE