877
FXUS63 KDLH 232143
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
443 PM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Isolated storms likely through early this evening. Severe
  weather is not expected.

- Highly conditional chance of severe thunderstorms Monday and
  Monday night (risk level 2 out of 5). All severe hazards are
  possible and will be dependent on storm mode and timing.

- Slight chance of non-severe storms Tuesday then quieter
  Wednesday. Thunderstorm chances return Thursday night and
  Friday.

&&

.DISCUSSION...
Issued at 443 PM CDT Sun Jun 23 2024

A broad upper low centered over north-central Ontario this
afternoon will propagate southeastward tonight into the western
Great Lakes and New England by 12Z Monday. Showers this morning
over much of the Northland gave way to mostly sunny to partly
cloudy skies this afternoon. The sunshine allow temps to climb
into the middle and upper 70s, except in the Arrowhead where
clouds loitered. Those temps and the low-level moisture flux
from this morning`s rain allowed MLCAPE values to push into the
750-1250 J/kg range this afternoon, more than sufficient for a
few isolated storms to develop. With the limited instability and
ample 0-6 km shear of 45-55 kts, a few storms may briefly become
strong with small hail to half-inch diameter, wind gusts up to
40 mph, occasional cloud-to-ground lightning, and brief heavy
rain. The storms should taper off through early evening with the
loss of daytime heating and use of available instability. Patchy
fog may develop tonight in response to clearing skies, light
winds, and recent precipitation.

The main focus for Monday through early Tuesday morning is the
highly conditional potential for strong to severe thunderstorms
on Monday afternoon into Monday night. A warm front will be
lifting north towards the CWA through the day Monday, bringing
WAA and moisture advection (PWAT of 1.5-1.9") into the area.
This will result in very warm temps tomorrow for the southern
half of the CWA, with highs in the low to mid 80s. Aloft, a
steep elevated mixed layer will be moving into the region, with
mid-level lapse rates increasing in excess of 8-8.5 degC/km by
the late afternoon and early evening hours on Monday. The
resulting MLCAPE values are expected to become high to possibly
extreme, with models showing highest amounts around 3000-3800+
J/kg. This high instability will be combined with a favorable
shear environment, where 0-6 km bulk shear magnitudes will be
around 45-50 knots. Given the favorable thermodynamics and
dynamics at play tomorrow, the SPC has our CWA highlighted in a
Slight Risk, with the main focus on very large hail and
damaging winds, although tornadoes cannot be ruled out if storms
can become surface based near the warm front.


There is one major caveat to mention for tomorrow`s severe
weather potential, which is that there will be an appreciable
cap present through the day. This greatly decreases confidence
for tomorrow, which is currently still low. The aforementioned
EML will be warming temps around the 700-800mb layer to 12-16
degC, increasing MLCIN above 200-300 J/kg by the late afternoon
hours tomorrow. There is some suggestion from a few CAMs that
this cap will be able to be overcome by the early evening hours
tomorrow. This is most likely a result of a combination of a
surface trough/occluded front advancing from the west and the
nocturnal LLJ strengthening and allowing elevated convection to
develop.

Provided that the cap is able to be overcome tomorrow (which is
far from certain), the two primary severe hazards will be very
large hail up to 2" in diameter and damaging winds up to 75 mph.
Large hail will be most likely in north-central Minnesota,
where convective initiation will be occurring near an
approaching cold front and MUCAPE will be abundant. Storm mode
from the CAMs has been highly variable between the different
models. However, there is some consensus that briefly discrete
cells will be transitioning more linear Monday evening. This
change in storm mode would limit the large hail potential to
fairly early in the event with damaging winds becoming the main
hazard as convection propagates eastward. Storm mode will also
determine the tornado potential tomorrow, with a tornado or two
being possible if convection is able to remain more discrete.
There is plenty of low-level curvature in hodographs, with high
0-1km SRH of 100-200 m2/s2. As storm mode becomes linear, a
QLCS tornado may also be possible. However, damaging winds are
the main concern with a linear storm mode.

It is worth mentioning that if a MCS is able to develop by the
late afternoon hours tomorrow in western MN, a derecho producing
winds to or possibly in excess of 75 mph is not out of the
question for tomorrow, mainly occurring south of U.S. 2 across
the CWA. In the latest Day 2 Convective Outlook from SPC, this
potential has been highlighted with a 15% hatched area for
damaging winds. However, this potential is still highly
dependent on the cap breaking at the right time and is uncertain
given the disagreements among the models. Overall, tomorrow`s
severe weather potential is shaping up to be either a "boom or
bust" type event.

One final note about tomorrow is that flash flooding is
currently not expected, as these storms will be moving through
the area fairly quickly and QPF will likely remain under 1.5
inches by early Tuesday morning. While widespread flooding is
unlikely, ponding on roadways and minor flooding of low-lying
areas will still be possible given that soils are well saturated
across the CWA.

The progressive pattern continues on Tuesday with a shortwave
trough propagating eastward across the region and a weak cold
front diving southeastward out of Canada during the afternoon
and evening. A few showers or storms may percolate along the
boundary. Neither severe weather nor additional flooding are
expected with the Tuesday storm chances. High pressure makes a
one-day-only appearance for Wednesday with quieter conditions
expected.

Another surge of warm air aloft will accompany a
northward moving warm front Thursday. Isentropic forcing for
ascent over the warm sector will lead to chances of showers and
possibly thunderstorms. The precip chances appear to hold off
until late afternoon or evening and spread northward with time.
Precip chances persist on Friday as an area of low pressure
propagates northeastward across the region. A cool front will
follow Friday night with high pressure to return on Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1245 PM CDT Sun Jun 23 2024

Isolated to scattered showers and thunderstorms are expected this
afternoon with ceilings varying between MVFR and VFR. As high
pressure builds this evening into tonight, expect improvement to VFR
areawide. Fog development late tonight has seen a noticeable upward
trend in recent model runs, especially for KHIB. Given the strong
upward trend for fog in KHIB tonight, visibility was reduced to
LIFR. Other terminals likely to see at least IFR fog tonight will be
DLH and HYR. Once fog dissipates, VFR conditions will once again
return for Monday morning.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 443 PM CDT Sun Jun 23 2024

Light winds of around 5 knots persist tonight. With a weak
pressure gradient overhead, the wind directions will be
influenced by terrain and onshore flow, and will be variable by
location and time. Low pressure will move eastward across the
region Monday and Monday night. Expect winds to become
southeasterly and easterly gradually backing northeast,
particularly in the southwest arm of the lake, by evening. Wind
speeds will increase to 5 to 10 knots with gusts up to 15 knots.
There is a chance of thunderstorms, mainly Monday evening,
which may be strong to severe. Hail up to an inch in diameter is
possible. Strong winds are not out of the question. There is a
small chance of wind gusts of 45 to 60 knots if storms coalesce
into a line during the late afternoon or evening. Winds turn
southwesterly and strengthen on Tuesday to 15 to 20 knots with
gusts of 18 to 25 knots. A Small Craft Advisory may become
necessary. A cool front will propagate southeastward Tuesday
afternoon and evening. Winds will veer northwesterly behind the
front and wind speeds will diminish.

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...None.

&&

$$

DISCUSSION...Huyck/Unruh
AVIATION...Unruh
MARINE...Huyck/Unruh