485
FXUS63 KDLH 151127
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
627 AM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Showers and thunderstorms today and tonight. Severe weather is
  not expected, but heavy rainfall could cause localized minor
  flooding mainly in northwest Wisconsin tonight (~25% chance).

- Isolated strong to severe thunderstorms are possible late
  Sunday afternoon and evening (~5% chance). Large hail and
  strong winds are the main threats.

- The threat for very heavy rain and flash flooding is
  increasing Monday through Tuesday (~35% chance), and scattered
  strong to severe storms capable of producing large hail are
  also possible (15% chance) Monday afternoon into Monday night.

&&

.DISCUSSION...
Issued at 452 AM CDT Sat Jun 15 2024

Showers have been persistent for parts of northeast Minnesota
this morning with some lift from a passing wave aloft. This area
of rain will continue but gradually diminish around mid-day.
Then, increasingly strong southerly flow containing warm air and
moisture will advect northward this afternoon into tonight, and
in association with a broader shortwave passing by aloft, an
area of rain and embedded thunderstorms is expected to develop.
PWATs rising to 1.50"-1.75" will be supportive for heavy rain,
mainly in northwest Wisconsin, through early Sunday morning. NBM
probabilities for >1" are ~40%, and >2" about 10%. Most model
ensembles are in good agreement for around 1"-2", and with this
first round of rain being fairly progressive, the threat for
flash flooding will be pretty low, but about 25% chance for some
localized minor flooding given already saturated soils from
previous rains.

Strong warm air advection on Sunday will lead to some pretty
impressive instability building, though we will also have a
strong cap in place. This will combine with weak subsidence
aloft to suppress thunderstorm potential (but not completely).
If we can get the cap to bust, there`s potential for 2-3k J/kg
of MUCAPE to be realized. The latest short-range models suggest
a weak cold front could act as an initial trigger for
thunderstorms late Sunday evening. Given the initially elevated
nature of these storms, large hail will be the main threat (5%
chance). But if they can get organized, they could form a line
as they traverse east into northwest Wisconsin Sunday evening,
and then a threat for damaging winds could develop (5% chance).
These storms should push east late Sunday night.

Another threat Sunday will be some pretty hot temperatures with
some sunshine before storms develop. Highs in the upper 80s are
expected in east-central Minnesota and northwest Wisconsin.
Those sensitive to heat, especially without effective cooling
or adequate hydration, will be most at risk for being affected
by these toasty temperatures.

After a very brief potential break in rain for a time late
Sunday night, the next round is expected Monday morning as
a strong and very moist southwesterly jet sets up aloft,
attendant with several passing upper level waves. A very strong
push of warm/moist southerly flow at the surface will develop
Monday afternoon, and models continue to very highly suggest
that there will be strong frontogenesis in the form of a warm
front that will set up somewhere in the upper Midwest. At this
point, it`s looking most likely anywhere from southern Minnesota
up to northern Minnesota, with a west-to-east axis from the
Dakotas into Upper Michigan. It`s still unclear where exactly in
this area the front will set up, but there`s starting to be a
little more agreement in recent model runs. Another piece of
uncertainty is how transient the front will be. If it becomes
quasi-stationary for a time, then the threat for localized,
high-impact flash flooding becomes a real possibility. If it has
gradual movement, then the threat for flash flooding still
remains high, but impacts could be moderated a bit and more
spread out. At this time, it looks like the front may be more
slowly moving (i.e. transient), but this could certainly
change. Either solution is not a good one, because with PWAT
values potentially reaching around 2" (just about as high as
they ever get around here), the threat for flash flooding
somewhere around the region Monday evening through Tuesday is
increasing (~35% at this time). Model soundings are suggestive
of deep saturation in the low levels, which means warm rain
processes more commonly found in tropical regions (collision-
coalescence) may occur here, and this is very efficient at
producing heavy rainfall accumulations.

With elevated instability increasing Monday night, there is also
a threat for some scattered severe storms (~5-15% chance). Given
that most of these will be elevated, large hail will be the main
threat, and the potential for severe storms will also be
dependent on where the warm front sets up.

Going into Tuesday, a cold front is likely to pass through and
bring more chances for scattered severe storms (~5-15% chance).
Damaging winds may be the greatest threat with these as storms
likely form into a line that passes through from west to east
and gradually ends both the heavy rain and severe storm threat
around Tuesday evening or so.

Perhaps a break in the active weather on Wednesday as models
suggest possible high pressure, then it looks like potentially
more active weather late-week into next weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 627 AM CDT Sat Jun 15 2024

Area of showers affecting HIB/INL this morning could result in
brief MVFR visibilities, but otherwise VFR this morning. Winds
will increase from the south today and remain gusty into tonight
with gusts a few knots above or below 20 knots expected. Another
round of rain will approach from the southwest this afternoon,
affecting BRD/HYR/DLH mainly going into this evening. With this,
ceilings are expected to gradually fall to IFR and MVFR
visibilities are expected at times. Some embedded thunderstorms
are possible, especially at HYR, this evening and overnight.
Even if rain doesn`t affect HIB/INL, ceilings are still expected
to fall to IFR with plenty of low level moisture moving in from
the south.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 426 AM CDT Sat Jun 15 2024

Northeast winds develop today from around 5-10 kt, gusting up to
20 kt this afternoon. Waves up to 2 or perhaps 3 ft locally are
expected. Winds only slightly weaken tonight into Sunday,
remaining east to northeasterly. Rain and thunderstorms are
expected tonight through Sunday morning, especially along the
South Shore. Scattered strong to severe storms capable of
producing large hail or strong winds are possible Sunday late
afternoon and evening (~5% chance).

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...JDS
AVIATION...JDS
MARINE...JDS