619
FXUS63 KDLH 302326
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
626 PM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Chance for heavy rain and possible flash and areal flooding Monday
afternoon into Tuesday morning. An isolated severe storm possible
Monday evening but heavy rain is the primary concern.

- Another system with more rain chances late Thursday through
Friday. Heavy rain could be possible again.

-Temperatures warming through the week.

&&

.DISCUSSION...
Issued at 333 PM CDT Sun Jun 30 2024

A beautiful day today with high pressure bringing mostly clear skies
and a dry air mass (dewpoints in the 30s and 40s!). Expect a fairly
calm night with some mid to high clouds moving in. The initial
vestiges of returning moisture overnight could lead to a couple
morning sprinkles through tomorrow midday.

Through the day tomorrow, a broad upper level shortwave builds in
across the northern Rockies and Upper Plains, along with a plume of
Gulf of Mexico moisture surging northward. PW is again forecasted to
be in the 95th percentile or greater by tomorrow evening and
overnight, with values nearing 2 inches. This saturation is present
through the column, with dewpoint depressions of 1-2 degrees or less
up through 500mb. Model soundings show a classic warm rain setup
with freezing levels near 500mb and warm cloud layers of 10kft
pushing into the area by midday tomorrow and warm cloud layers of up
to 13kft overnight into Tuesday morning. This is a concerning
potential heavy rain set up, on top of areas that have already
received 150-300 percent of their normal June rainfall (the wettest
month of the year). One thing working in our favor is that despite
mean winds being fairly parallel to the front and storm motion,
cloud layer winds should be decently fast and corfidi vectors are
largely 15-20 knots or greater, which should reduce overall
widespread training of storms.

Flooding was observed last Friday in some areas with rainfall totals
of 1-2", which have not had enough time to recover. The majority of
rivers are running above normal and latest data indicates 55 to 70%
soil saturation (also above normal). Flash flood guidance shows
rainfall of only 1-2.5" in several hours would be able to produce
flash flooding. The most sensitive of these antecedent
conditions is across the northern portion of the Northland, in
the Iron Range, across Lake Vermilion and the Rainy River
headwaters, across the St. Louis River headwaters (including the
Embarrass and Cloquet Rivers), and in the MN Arrowhead,
including along the North Shore. This is also where some of the
heaviest rain is expected to fall Monday night into Tuesday
morning. Current guidance suggests a widespread 0.75-1.5"
possible across these northern areas, but warm rain processes
could easily overachieve, with localized areas of 2"+ possible.
HREF guidance shows a 30% chance of rainfall exceeding 1" in 3
hours around midnight and into the morning hours Tuesday. For
these reasons, we`ve issued a Flood Watch across the areas of
greatest concern, running midday Monday through Tuesday evening.

The precipitation Monday-Tuesday is expected have a bi-modal
distribution across the Northland, with two areas of heavier
rain. One is outlined in the paragraph above. The second should
be over the far southern tier of counties in the CWA, from Mille
Lacs and eastward across much of the St. Croix and Chippewa
River basins. Here, a round of heavy rain is possible overnight
into Tuesday morning, but rainfall values are slightly less (one
inch or below) and we have a little more room for water to go
in rivers, lakes, and soils. Should rainfall values trend
upwards, a Flood Watch may be needed here as well.

An isolated severe storm could be possible late Monday afternoon and
evening, as the shortwave and attending front pushing into the area.
However, we will be lacking very good instability, and the best
shear and forcing space comes only as far eastward as the I-35 and
U.S. 53 Highway corridors. Along that line and west, there could be
an occasional thunderstorm that produces hail up to an inch in
diameter and a breif damaging wind gust up to 60mph.

A hint at ridging moves in Wednesday, but we may stay under
northwesterly flow which could continue to bring some scattered
light showers and partly cloudy conditions.

Late Thursday and into Friday, a deeper shortwave trough with a cut
off low is progged to push over the International Border and sweep
over the Upper Great Lakes. With good synoptic forcing and another
round of attending deep moisture, this will be another one to watch
for heavy rain potential.

Temperatures rise through the week, with high temps nearing 80 by
July 4th, which is right around to slightly above normal for the
time of year.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 623 PM CDT Sun Jun 30 2024

Light and variable winds and mostly clear skies tonight. VFR
conditions. Winds gradually increase from the south starting
Monday morning, and gusts from 20 to nearly 30 knots can be
expected by Monday afternoon as the next weather system
approaches from the west. Clouds will increase and there`s a
slight chance for showers Monday morning (15-20% chance). Then,
better chances that showers and possibly thunderstorms could
arrive at INL/BRD late-afternoon Monday. MVFR ceilings and
visibilities could be possible in the late-afternoon.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 333 PM CDT Sun Jun 30 2024

A nice calm high pressure day today has resulted in a light lake
breeze circulation for some nearshore areas. Winds stay fairly calm
overnight, becoming east to northeasterly through the day Monday.
These winds are largely expected to be less than 15 knots across
Western Lake Superior, but near the Twin Ports some gusts near 20
knots are possible with 2-3 foot waves Monday afternoon. Tuesday
morning, some stronger southeast winds are expected to have built
overnight, with gusts of 15 to 20 knots through midday before winds
become southwesterly and decrease. Rain showers and embedded
thunderstorms are expected to increase in coverage overnight into
Tuesday morning, and continue through the day Tuesday. No severe
storms are expected, but heavy rain is likely. A lingering moist
airmass could lead to pockets of dense fog, especially as winds
calm Tuesday evening.

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

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Flood Watch from Monday afternoon through Tuesday evening for
     MNZ010>012-018>021.
WI...None.
MARINE...None.

&&

$$

DISCUSSION...Levens
AVIATION...JDS
MARINE...Levens