Sandy, Minnesota Weather Forecast Discussion

206
FXUS63 KDLH 080850
AFDDLH
Area Forecast Discussion
National Weather Service Duluth MN
350 AM CDT Mon Sep 8 2025
.KEY MESSAGES...
- Patchy frost early this morning.
- Showers and thunderstorms return this afternoon into Tuesday.
  There is a small chance (~20%) for a few of the storms to
  become strong Monday afternoon and evening. Large hail and
  gusty winds are the main threats although a tornado cannot be
  ruled out.
- Rainfall this afternoon through Tuesday morning may be locally
  heavy and lead to localized flash flooding.
- High pressure brings quieter weather for the middle of the
  week.
- Precipitation chances return Friday through the weekend.
&&
.DISCUSSION...
Issued at 350 AM CDT Mon Sep 8 2025
Today through Tuesday...
A southwesterly nocturnal low-level jet developed over eastern
South Dakota and southwest Minnesota early this morning. The
strengthening winds aloft led to an increase in isentropic
ascent over a warm frontal zone over southern and portions of
central Minnesota. GOES-East infrared and night microphysics RGB
products featured a growing stratus field in response to the
ascent. Meanwhile northwest flow continued aloft over the region
and carried a layer of high altitude stratus over portions of
northeast Minnesota. As of 3 AM temperatures across the
Northland ranged from middle 30s to low 40s with several pockets
of low 30s. A surface high pressure axis was located over west-
central Wisconsin into central Minnesota. The area included in
the Frost Advisory was mainly on track and was dependent on
winds becoming calm. The cloud cover over northeast Minnesota
should keep temperatures a bit warmer than elsewhere.
Cyclogenesis over the western High Plains associated with an
eastward propagating shortwave trough will continue this morning
tightening the frontal zone from western North Dakota into
southern Minnesota. The warm front will propagate northeastward
today and is expected to stretch from near Fargo, ND to Moose
Lake, MN to near Rhinelander, WI by 21Z today and advance
farther north into a Grand Forks, ND to Silver Bay, MN line by
09.03Z. Isentropic ascent over the frontal zone is forecast to
continue and scattered showers may develop over central and
portions of northeast Minnesota by late morning/early afternoon
today.
Tall skinny CAPE profiles in the warm sector will provide
500-1500 J/kg with effective shear of 20-30 knots. Hodographs
are cyclonically curved below 3 km and should provide ample
updraft enhancement of any storms which can develop in the warm
sector. Model soundings do reveal a capping inversion which may
erode by 00Z tonight. The main question then becomes whether we
see widespread convection or more intense scattered to isolated
storms. The low-level jet will strengthen again this afternoon
and evening over the warm sector nosing into the Arrowhead by
early evening. The ascent and added convergence from the
strengthening jet should support elevated storms, which may be
the dominant mode if the capping inversion remains in place.
The effective shear and hodograph parameters suggest a
potential for storm-scale organization. Supercells are not out
of the question, which would support a risk of damaging wind
gusts to 60 mph, large hail to quarter-size (with a few stones
possibly as large as ping pong balls), and a small risk of a
tornado. If convection is more widespread, the modest potential
instability will likely result in strong, but not severe storms.
The greatest risk is found from the Brainerd Lakes into the
I-35 corridor this afternoon stretching farther north into the
Iron Range by early evening.
In addition to the severe weather risk, there is a potential
for locally heavy rainfall. Isentropic ascent will persist north
of the warm front which will lead to a broad area of light to
moderate rainfall. Moisture flux into the frontal zone will
support efficient rain production and embedded thunderstorms.
Thus there is a potential for localized flash flooding tonight
from central Minnesota into the I-35 corridor and northwest
Wisconsin as far north as the Arrowhead. The initial risk area
will be near and north of the warm front and will spread east
into northwest Wisconsin tonight.
The warm front will stall overnight and then gradually
propagate southward early Tuesday morning as a cold front.
Isentropic ascent will persist over east-central Minnesota,
northwest Wisconsin, and the Arrowhead through Tuesday, shifting
eastward gradually with time. Look for widespread light rain
and embedded thunderstorms to continue and gradually end from
west to east with time. Localized heavy rainfall will remain
possible over northwest Wisconsin along with the risk of
localized flash flooding.
Tuesday night through Thursday night...
An upper-level ridge will build over the northern Plains for
midweek through Thursday. Temperatures will be near normal
during the period with relatively quiet weather forecast.
Friday through next weekend...
A cutoff low is forecast to propagate southeastward over
northern Ontario and northern Quebec to end the work week. A
shortwave trough will extend to the southwest of that feature
and will support precipitation chances Friday and Saturday. A
few storms are possible during that time. Temperatures may trend
slightly cooler, but remain near normal for Sunday in the wake
of a modest cold front.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1246 AM CDT Mon Sep 8 2025
Surface high pressure centered over northern Indiana will drift
farther east overnight. Light southerly winds are forecast
through sunrise over the terminals. Clear skies will permit
efficient radiational cooling and fog development at HIB, BRD,
and HYR. Clouds may develop over central Minnesota early this
morning and winds may pick up into the 3 to 5 knot range as the
surface pressure gradient gradually tightens overnight. Both of
those factors may interfere with fog development. Introduced
MVFR and IFR visibility with this update and will keep an eye on
trends. Also included LIFR at HIB and HYR partially based on
persistence with the past several mornings. Showers and a few
thunderstorms are forecast this afternoon and evening. Still
have some uncertainty in the timing of the precipitation and
best thunder risk. Opted to continue with VCSH for now. Will
likely add PROB30s or prevailing SHRA/TSRA later this morning.
&&
.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 350 AM CDT Mon Sep 8 2025
Southerly winds will veer southwesterly later this morning and
strengthen through the day. By tonight gusts of 20 to 25 knots
are forecast along the South Shore which will create hazardous
conditions for small craft from Bayfield to Saxon Harbor and
over the eastern portion of the Outer Apostle Islands. A Small
Craft Advisory is in effect for those areas from 10 PM tonight
until 10 AM Tuesday.
Showers and thunderstorms are forecast late this afternoon
through Tuesday. Southwest winds will persist and gusts will
decrease to 10 to 20 knots. Winds will weaken Tuesday night and
should back northerly by Wednesday morning.
For the open water discussion, refer to the NWS Marquette Area
Forecast Discussion at weather.gov/mqt.
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Frost Advisory until 8 AM CDT this morning for MNZ010-011-019-
     037.
WI...Frost Advisory until 8 AM CDT this morning for WIZ001>004-008-
     009.
MARINE...Small Craft Advisory from 10 PM this evening to 10 AM CDT
     Tuesday for LSZ121-148-150.
&&
$$
DISCUSSION...Huyck
AVIATION...Huyck
MARINE...Huyck

NWS DLH Office Area Forecast Discussion