186
FXUS63 KFGF 012346
AFDFGF

Area Forecast Discussion
National Weather Service Grand Forks ND
646 PM CDT Mon Sep 1 2025

.KEY MESSAGES...

- There is a level 1 out of 5 risk for severe storms Tuesday
  afternoon in southeast North Dakota into west-central
  Minnesota. Main hazards include hail to the size of quarters
  and wind gusts to 60 mph.

- Below average temperatures will occur mid to late week, with
  morning frost likely over parts of the region. This includes a
  30% chance for below freezing temperatures in northwest
  Minnesota Thursday morning.

&&

.UPDATE...
Issued at 637 PM CDT Mon Sep 1 2025

Thunderstorms have developed along the periphery of a synoptic
low over the International Border. Occasional severe hail is
possible with these storms as effective bulk shear is just
enough to facilitate supercells. Thunderstorm activity will
continue this evening and overnight, but the severe threat
should mainly remain confined to this early evening.


&&

.DISCUSSION...
Issued at 214 PM CDT Mon Sep 1 2025

...Synopsis...

Weak upper trough currently resides over the eastern Dakotas
this afternoon. This will aid in widely scattered showers and
storms this afternoon into evening. While not likely, cannot
rule out a brief funnel in eastern North Dakota given enhanced
stretching potential and weak surface convergence aided by
topography of the western Red River Valley. Additionally,
couldn`t rule out small hail in northeast North Dakota late
afternoon into evening should additional thunderstorms develop
(20% chance of occurring).

Upstream into AB/SK/MB, a potent shortwave trough can readily
be seen. This will be driver of the upcoming week`s below
average temperatures, shifting today`s summer-like conditions
drastically toward fall-like conditions: cool, breezy, and
cloudy with showers starting tomorrow for those north of I-94
corridor.

On the head of the incoming shortwave trough housing the cold
air mass will be a cold front to sweep north to south across the
region late tonight through the day Tuesday. Scattered showers
and thunderstorms are forecast with the cold front given strong
forcing for ascent to utilize sufficient moisture and
instability ahead of the front. With the incoming shortwave
trough, kinematics/shear increases some to introduce potential
for severe storms Tuesday afternoon (more details below).

The initial shortwave trough will deepen as it enters our
region, while slowing its progression. Ensemble guidance
continues to strongly agree the amplifying shortwave trough to
stall into an upper low near the Upper Midwest and Great Lakes
regions mid to late week. This is supported by reinforcing
shortwave and additional feed of seasonably cold continental air
masses sliding out of northern interior Canada. This should
continue to support colder than average temperatures into late
week, particularly for Minnesota locations closer to the now
stalled and well developed upper low. This will drive potential
for frost/freeze Thursday, as well as potentially
Friday/Saturday (more details below).

Cooling temperatures aloft and additional shortwave
impulses moving through northwest flow aloft will also aid in
supporting scattered shower activity into Wednesday and perhaps
Thursday. Cooling temperatures aloft may even support lake
effect processes supporting persistent, localized scattered
light shower activity. At this time, there is very little
support offered by guidance pointing toward potential light snow
in our area as temperatures are forecast to be just warm enough.
However, there remains a small subset of guidance that allows
very brief period of light, non accumulating snow within
northwest Minnesota early Wednesday morning and/or Thursday
night/Friday morning. Chance of this to occur is too low to
include in the forecast, however (around 10%).

...Severe storm risk Tuesday...

Currently favored timing of the front brings it near the I-94
corridor by the afternoon. This may allow instability on the
order of 1000 to 2000 J/kg to develop amid temperatures into the
upper 70s and low 80s as well as dew points well into the 60s.
Should this occur within our area, thermodynamically we should
be primed for thunderstorms to develop given the strong synoptic
and low level forcing for ascent. Cooling temperatures aloft
above rich theta-e below would also allow for gusty downdraft
winds, potentially bringing isolated gusts to 60 mph.

However, winds modestly increase throughout the column,
allowing for sufficient shear to help organize storms. Shear is
not anticipated to be strong, but multicells may allow for hail
to the size of quarters. Other hazards such as tornadoes and
flooding are not anticipated given fast storm motion, limited
moisture and instability.

...Below average temperatures mid to late next week...

With temperatures of this degree moving into the region, it is
reasonable to expect some potential for frost/freeze in our
area, particularly the typical cold spots of northwest and
west-central Minnesota. For frost to form, any wind generally
above 7 mph will very much limit its development. However,
calmer and clearer nights will hold relatively best potential
(namely Wednesday night/Thursday morning as well as Saturday
morning).

There is also potential for freezing temperatures, particularly
Thursday morning, within our area. As of now, there is a 30%
chance temperatures 32F or colder Thursday morning within
portions of northwest Minnesota, and more like 10% elsewhere.
This would be seasonably early frost/freeze if it occurs.

Factors that lower confidence include influence of potential
clouds (perhaps lake effect driven) as well as wind to mitigate
radiational cooling as well as frost formation.

An additional shot of cold air may introduce an additional
chance to see frost/freeze in our area behind reinforcing cold
air mass intrusion Friday/Saturday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 637 PM CDT Mon Sep 1 2025

Showers and thunderstorms may impact TAF sites this afternoon
with a low risk for hail. Winds will shift to northerly and
northwesterly after 06z tonight eventually crossing all TAF
sites by the end of the period. Accompanying this wind shift
will be potential showers and thunderstorms once more. MVFR
ceilings should also arise at GFK/TVF/BJI as it moves through
tomorrow morning but all sites should become VFR by the end of
the TAF period.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.

&&

$$

UPDATE...Perroux
DISCUSSION...CJ
AVIATION...Perroux