Severe Thunderstorm Warning 20, NWS Bismarck, ND

Area Forecast Discussion
National Weather Service Bismarck ND
321 PM CDT Wed Jun 18 2025

.KEY MESSAGES...

- Active pattern continues, with periodic chances for showers
  and thunderstorms through the rest of the work week and into
  the weekend.

- Strong to severe thunderstorms are possible this afternoon
  through the weekend.

- Temperatures will warm up to above normal Thursday through
  Saturday, before cooling down to start next week.

&&

.DISCUSSION...
Issued at 321 PM CDT Wed Jun 18 2025

This afternoon, the synoptic pattern over North Dakota was
characterized by northwest flow in between downstream troughing
over the Midwest and shallow ridging over the Northern Rockies,
while a more potent low was developing off the Pac NW coast. At
the surface, the center of a low was analyzed in northeast
Montana, and a weak north-south boundary extended across central
North Dakota, demarked by a wind shift and a somewhat agitated
cu field. Widely scattered showers and thunderstorms are
attempting to develop, mainly across the south central, in a
moderately unstable environment but one that has very weak
shear. We would expect rather broad convective initiation in
this area but not much concern for any severe weather in the
immediate future, although any storm with a more robust updraft
could produce small hail and gusty winds.

Upstream, addition cu and precipitation is attempting to become
more pronounced in northeast Montana and southern Saskatchewan,
closer to the surface low and attendant trough. SPC mesoanalysis
page has shear approaching 30 knots in this area which is still
quite marginal, but stronger than where other convection is
ongoing. Guidance suggests that bulk shear will be increasing in
speed through the afternoon and into the evening as an upper
shortwave moves through, and expecting this to be the primary
wave of thunderstorms as they moves southeast across the
forecast area through this evening. We are still thinking the
primary threats will be hail up to the size of quarters and wind
gusts up to 60 mph, but if we get any supercell development,
that max hail size starts to increase quickly. This would likely
not occur until the evening hours when there is higher
confidence in shear increasing. Once storms taper off and exit
to the east tonight, expect a calm night with lows in the 50s.

Temperatures warm on Thursday as shallow ridging flattens, with
forecast highs in the lower 80s to lower 90s. We are carrying
mention of isolated severe thunderstorms (level 1 out of 5), but
capping is a concern with mid-level height rises. Thinking this
is a scenario where we might not get any convection at all, but
if we do get a storm or two to develop, they will likely be
strong to severe, with elevated buoyancy and strong shear across
the forecast area.

The ceiling for severe thunderstorm hazards begins to increase on
Friday, as flow aloft turns southwesterly and low-level moisture
advection increases, producing a favorable environment for severe
thunderstorms. A warm front is expected to be drifting across the
region, with some capping potential but a few upper shortwaves
traversing the mean flow, along with a low-level jet kicking in, are
likely to provide enough forcing for convective development
eventually. Deterministic guidance has been steady in
advertising around 50 knots of 0-6km shear overlapping with
very strong instability, highest in the south central and east.
The orientation of storm level flow and shear vectors favors
upscale growth as storms progress, with increasing confidence in
a linear mode and potential MCS. If initial storms break
through capping, they would likely be discrete, before more
widespread storms in the evening that see upscale growth as they
move east across the area. The question is then where this ends
up occurring, with some signs of initial storm development
across central North Dakota before the eventual upscale growth
as it moves into the eastern part of the state. We are
advertising scattered severe thunderstorms possible on Friday
across western and central North Dakota (level 2 out of 5), and
are not getting too specific with hazards yet, but certainly is
a day to watch especially if you have outdoor plans that
evening and overnight.

Stout southwest synoptic flow continues on Saturday, with a
continued signal in machine learning guidance and the ECMWF EFI for
another day of potential severe thunderstorms. There is some
uncertainty in deterministic models on what sort of forcing will be
around and what mid-level heights trends look like, but regardless,
it will be another day to stay weather aware across the area. The
latest NBM does favor precipitation chances across the north
compared to the south. The other forecast concern on Saturday is for
heat indices approaching 100 degrees in the southern James River
Valley, with air temperatures in the lower to mid 90s and dew
points potentially around 70 degrees F.

A more pronounced, embedded wave moves through Sunday into Monday,
with precipitation chances continuing but the potential for any
severe weather shifting off to the east. A tightened surface
pressure gradient from a surface low skirting by will lead to
elevated winds on Sunday, although the ECMWF EFI isn't sold on
anything too strong. Temperatures on Sunday will vary significantly
across the state, with highs ranging from the mid 60s northwest to
lower 90s southeast as the system moves through.

Quiet and a bit calmer weather is expected to start next work week,
with highs mainly in the 60s on Monday as a cooler air mass settles
in. Low precipitation chances remain through the end of the extended
period as southwest flow aloft persists, although the severe weather
potential is low with seasonably cool temperatures through most of
the work week.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1245 PM CDT Wed Jun 18 2025

Overall VFR conditions are expected through the period.
Scattered showers and thunderstorms are possible through the
first half of the TAF period, with only KDIK with low enough
potential for precipitation to not include PROB30 group with
this update. Some thunderstorms could be strong to severe,
especially north, with KMOT the most likely terminal to be
impacted. Generally westerly winds could become gusty and
erratic around any thunderstorms, and winds will become light
and variable overnight into Thursday morning.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...Jones
AVIATION...Jones

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Special Weather Statement
National Weather Service Bismarck ND
431 PM CDT Wed Jun 18 2025

NDZ017-018-182215-
McKenzie ND-Dunn ND-
431 PM CDT Wed Jun 18 2025

...A STRONG THUNDERSTORM WILL IMPACT NORTHWESTERN DUNN AND SOUTH
CENTRAL MCKENZIE COUNTIES THROUGH 515 PM CDT...

At 431 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles east of Theodore Roosevelt National Park North Unit, or 16
miles southeast of Watford City, moving southeast at 30 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Theodore Roosevelt National Park North Unit, Oakdale, and Little
Missouri State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4767 10327 4770 10314 4767 10290 4755 10261
      4725 10297 4731 10303 4733 10303 4733 10305
      4755 10328
TIME...MOT...LOC 2131Z 301DEG 26KT 4759 10311

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

HAMILTON