Duluth, Minnesota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

859
FXUS63 KDLH 201140
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
640 AM CDT Sun Jul 20 2025

.KEY MESSAGES...

- Wildfire smoke will linger through 9 AM Monday morning. An
  Air Quality Alert is in effect for northern MN

- An active weather pattern overtakes the region beginning on
  Monday. Expect multiple chances for showers and storms through
  the coming week.

- There is a risk of severe storms Tuesday and Wednesday.
  Damaging winds, large hail, and heavy rain which could cause
  flash flooding are the main threats.

&&

.UPDATE...
Issued at 640 AM CDT Sun Jul 20 2025

Added a mention of sprinkles to the forecast north of a line
from Walker to Ely this morning. Showers have been weakening and
becoming less coherent over the past few hours. Still think
they`ll hang together long enough for a few dots of rain to make
it to the ground. No other changes.

&&

.DISCUSSION...
Issued at 411 AM CDT Sun Jul 20 2025

Summary...

Relatively quiet weather today and tonight will give way to a
more active period thereafter. Several rounds of thunderstorms
are possible during the Tuesday-Saturday period. The threat each
day is somewhat conditional with weak forcing overall and stout
capping possible. Should storms develop the main concerns will
be a risk of damaging wind gusts, large hail, and heavy rainfall
which may cause flash flooding.

Today through Monday...

A mid-level ridge is forecast to develop over the northern
Plains and Upper Midwest today and will further amplify on
Monday. Near the surface a broad area of high pressure will
slowly propagate eastward with time. Winds in the low levels
will typically be easterly today veering more southerly on
Monday. Warm theta-e advection on Monday will gradually raise
precipitable water values to 1.2 to 1.8 inches over the
Northland by 7 PM Monday evening (00Z Tuesday). The highest
values will be over central and north-central Minnesota arcing
back into northwest Wisconsin.

Beneath the building ridge, weak 700 mb frontogenesis may be
sufficient to generate a few showers over north-central
Minnesota late this morning into the afternoon. A few of the
CAMs (HRRR, RAP, NAMNEST, RRFS) maintain the showers over
eastern North Dakota and propagate them into north-central
Minnesota later this morning. The signal for precipitation is
not particularly strong thus we kept the forecast dry for the
moment. This may need to be reevaluated before 12Z should the
showers persist into northwest Minnesota. There is subtle
evidence of a weak MCV at the core of the remaining showers
which would enhance the precipitation potential as that feature
moves across northern Minnesota.

A similar progression is possible Monday morning as convection
over the Dakotas decays during the early morning hours. For now
we opted to keep the forecast dry until after 12Z Monday. There
has been a noticeable "wet" bias in the NBM PoPs in the medium
and extended forecast periods for at least the past 12 months.
Think that trend continues with the Monday shower and storm
chances. Given the weak forcing and subtle meso-beta scale
effects from decaying convection, it seems the PoPs are too high
by as much as a factor of 2.

Monday night through 7 AM Thursday...

This is clearly the most potentially active portion of the
forecast. Warm theta-e advection will continue over the northern
Plains and the Upper Midwest which will raise precipitable
water values to 1.5 to 2.2 inches. NAEFS and GEFS percentiles
place these values in the 90-99th percentile for late July.
ECMWF percentiles are also >90th percentile during this period.
Deterministic and ensemble solutions vary between members which
keep the atmosphere capped or largely capped and those which
seem to indicate one or several convective complexes developing.
Monday night appears to be the first chance for storms to
develop on the nose of a nocturnal low-level jet. Forcing and a
stout capping inversion seem to be the greatest limiting
factors. Effective shear around 20 knots would seem to indicate
any storms would be "upright" and generally lacking storm-scale
organization. That may be balanced by merging of cold pools
overnight, although the weak flow overall would seem to limit
that potential, too.

Tuesday will bring the next potential for storms. The
deterministic GFS seems to feature the development of a morning
convective complex which propagates northeast across the central
Minnesota and the Arrowhead through the day. The ensemble
members and other deterministic solutions represent a wide
variety of solutions. Some of these include afternoon
development of storms while others seem to hold back convection
until Tuesday night when a strong low-level jet is forecast
which could provide enough forcing to overcome the capping.
Precipitable water values and instability will be the greatest
on Tuesday and Tuesday night. Should storms develop, a damaging
wind and flash flooding risk is anticipated.

By Wednesday a cool front will begin to move into the area.
That boundary poses the greatest potential for overcoming the
stout elevated mixed layer over the region. PWATs will remain
high, although not quite as high as Tuesday. Low-level flow
should generally be parallel to the boundary which would suggest
a potential for "training" storms and a potential for flash
flooding.

SPC included our area in a Marginal Risk for severe storms on
Tuesday. WPC features a Slight risk of excessive rainfall
Tuesday and a Marginal risk for Wednesday. All of these seem
appropriate given the weak forcing and high precipitation
potential should storms develop.

Temperatures on Wednesday will be quite warm ahead of the
front. Highs will be in the upper 70s to upper 80s. Heat indices
may climb above 95 degrees for portions of the I-35 corridor
and northwest Wisconsin. Heat headlines may eventually be
needed. The main challenge in forecasting high temperatures and
heat concerns is whether convection develops the previous night
and whether skies clear the following day. At this point, I feel
it`s important to acknowledge the potential risk.

7 AM Thursday through Saturday...

Wednesday`s cool front may stall over the Upper Midwest and
provide focus for additional rounds of storms Thursday.
Confidence trends much lower beyond Wednesday due to the
unavoidable effects of successive days of possible convection.
Friday appears to be the quieter day before storm chances return
for Saturday.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 640 AM CDT Sun Jul 20 2025

Smoke appears to be playing a larger role in the reduced
visibility this morning than thought. Have (somewhat
aggressively) reduced visibility at the terminals today based on
current observations and near-surface smoke forecasts from the
06Z RRFS. Visibility impacts are difficult to tie directly to
smoke concentrations due to modeling limitations. As a result, I
have low confidence in the visibility forecast today and
conditions may improve quickly once the boundary layer begins to
mix in response to solar heating.

A few sprinkles may pass by INL and HIB this morning. Don`t
anticipate visibility reductions with the sprinkles. Expect
reduced visibility again tonight with the combination of smoke
and slowly increasing low-level moisture. An isolated shower or
storm cannot be ruled out after 21.06Z, although the better
chances appear to be after 21.15Z.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 411 AM CDT Sun Jul 20 2025

High pressure over the region will lead to relatively light
winds through the next few days. Wind speeds will increase
during the afternoon today and Monday, particularly in the
southwest arm. As the high pressure slides off to the east, the
pressure gradient over western Lake Superior will become
favorable for slightly stronger northeast winds. The strongest
winds of 10 to 15 knots with gusts up to 20 knots are expected
over the southwest arm Monday afternoon and evening. Otherwise
the main concerns relate the potential for thunderstorms Monday
through Thursday.

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.

&&

$$

UPDATE...Huyck
DISCUSSION...Huyck
AVIATION...Huyck
MARINE...Huyck