686
FXUS63 KBIS 271744
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1244 PM CDT Fri Jun 27 2025

.KEY MESSAGES...

- Scattered severe thunderstorms (risk level 2 out of 5) could
  develop across central North Dakota late this afternoon
  through this evening. Expected hazards include hail as large
  as tennis balls, damaging winds as high as 70 mph, and a
  tornado or two possible.

- There is a low chance (10 to 20 percent) for isolated strong
  to severe storms across parts of south central and eastern
  North Dakota Saturday afternoon and evening.

- Daily high temperatures through next week are mostly expected
  to range from the mid 70s to upper 80s. Today and Saturday
  will be humid for central and eastern North Dakota.

&&

.UPDATE...
Issued at 1205 PM CDT Fri Jun 27 2025

No significant changes for the early afternoon update. Stratus
continues to erode over central and into eastern ND, with mostly
sunny skies over most of western ND. There is some isolated mid
and high level cloudiness over northeast Montana into northwest
ND with maybe an isolated sprinkle or two reaching the surface.

Uncertainty remains for this afternoon and this evening in
regards to severe thunderstorm potential. Although CAM
solutions continue to vary but we don`t really see any CAM that
suppresses convection altogether. As the previous shift
mentioned the forcing for ascent remains subtle, but the CAMs
agree that there will be convection this afternoon and/or this
evening. The question is how will this play out.

Going back to yesterday and prior. There was more of a signal
for convection firing over western/central ND from the Canadian
Border south into South Dakota. Today it looks like the
potential for CI over southwest ND looks smaller but non-zero.
CAMS continue to indicate convection in the northwest/north
central and track southeast through central ND where a moist and
very unstable atmosphere will exist. The orientation of the
shear vectors to the surface boundary in the north central
suggest a possible mixed or messy mode. As you go farther south
into south central ND the more perpendicular orientation
suggests supercells may be more probable, but the atmosphere is
at least initially more capped. Initial CI, no matter where it
is will have the potential to be supercellular with very large
hail and possibly a tornado or two. Later in the period the
potential for activity to congeal into clusters or bowing
segments. A look at the latest HREF UH paintballs certainly
suggest a blend of short and long tracks. Short tracks may be
more favored in the north, with a blend central and longer
tracks favored south, if capping issues can be overcome.

Overall, no changes were made to the prior hazards of tennis
ball sized hail, 70 mph winds and a tornado or two.

UPDATE
Issued at 1001 AM CDT Fri Jun 27 2025

Visibilities have improved greatly across the advisory area,
therefore the Dense Fog Advisory has been allowed to expire.
Otherwise, we adjusted pops a bit, pulling our slight chance
pops back a little farther west to include convection currently
over Dunn county. Focus will now shift to afternoon/evening
convection.

UPDATE
Issued at 656 AM CDT Fri Jun 27 2025

Areas of dense fog continue over south central North Dakota this
morning, and the advisory for it remains in good shape. Webcams
show low visibility in some areas surrounding the advisory, such
as southern Ward and western Stutsman, LaMoure, and Dickey
Counties. But it does not expand far enough across these
counties to warrant an expansion of the advisory.

Isolated showers and the occasional thunderstorms continue to
migrate eastward from western into central North Dakota this
morning. The forecast was updated to reflect current trends, but
confidence in the evolution of activity this morning, and for
that matter the rest of the day, remains low.

Both the 06Z HRRR and NAMnest initiate severe storms at the nose
of a plume of low level moisture transport in the vicinity of
the Highways 2 and 200 corridors and along and west of Highway
83 late this afternoon, with upscale growth to the south and
east through the evening. Will be interesting to see if these
trends hold and what other scenarios the 12Z CAMs might have to
offer.

&&

.DISCUSSION...
Issued at 451 AM CDT Fri Jun 27 2025

A mid level low spinning into southwest Ontario early this morning
has left a low-amplitude transient ridge in its wake. Behind this
feature, southwest flow aloft remains in place from the Northern
Rockies to High Plains. Shortwave energy embedded in the southwest
flow aloft has maintained a few pockets of showers and thunderstorms
across western North Dakota. But so far, these have not been able to
advance into the much more stable air mass and deep layer subsidence
over the eastern two thirds of the state, which is where low stratus
has settled back in. In south central North Dakota, several webcams
and observations have been showing dense fog, enough so to prompt
the issuance of a Dense Fog Advisory until 10 AM CDT.

Isolated to widely scattered showers could percolate throughout the
state this morning and early afternoon. Do expect the low clouds to
retreat eastward and lift through the day, but that was also the
thought yesterday when clouds were much slower to retreat than
expected and never did clear the eastern half of the state. The
western half of the state should see some sunshine throughout the
day with highs in the mid to upper 80s. The eastern half will be at
least slightly cooler, even if the sun does come out.

The main forecast concern is the potential for severe thunderstorms
from central into eastern North Dakota late this afternoon through
this evening. Deep layer shear and buoyancy are forecast to be
abundant, with 0-6 km bulk shear increasing from around 40 kts in
the late afternoon to as high as 50 kts by sunset, and SBCAPE
increasing to at least 3000 J/kg (HREF mean) but possibly exceeding
4000 J/kg (HREF max and RAP). However, model soundings and two-
dimensional CIN fields do show enough mid level capping to suppress
convection, or perhaps even prevent it entirely, although the latter
of those two stated outcomes is at the very end of the forecast
spectrum, and every run of every recent CAM has initiated at least
one storm with notable UH tracks. Some forcing mechanisms will be
present, but not to a strong degree. At the surface, a lee trough/
pseudo-dryline is forecast to reach between Highways 85 and 83 by
late afternoon, which would likely be the focal point for convective
initiation. Mid to upper level forcing is ill-defined, but
deterministic models do maintain pockets of shortwave energy in the
persistent southwest flow aloft. Low level moisture transport could
aid in erosion of CIN, but mid level height tendencies are forecast
to remain neutral. All this leads to uncertainty on the location,
timing, and to a lesser extent even occurrence of convective
initiation. Having said that, the most likely outcome is still for a
few updrafts to be sustained through the LFC, resulting in severe
storms. Given perpendicular orientation of deep layer shear/wind
vectors to the lee trough, discrete supercells are the expected
storm mode, with very large hail being the hazard of greatest
concern. There will also be a smaller spatiotemporal window for a
tornado risk. HREF mean STP (1-2) and probability of STP greater
than 1 (50 to 80 percent) have both risen from previous forecast
iterations, and maximum values of each are focused in an area
enclosed by Highway 83, Highway 200, Highway 281, and the South
Dakota border. Cold pool dynamics will likely drive upscale growth
into a multi-cluster/linear MCS later this evening, though the size,
location, and timing of this remain very uncertain. This should
transition the main hazard to damaging winds. The threat for severe
weather should diminish around or shortly after midnight, at which
time MCSs simulated by CAMs are forecast to exit the forecast area.
However, there is still a low probability, as shown by the 06Z HRRR,
for outflow from the MCS to intersect a strengthening low level jet
to produce a narrow corridor of training convection in southeast
North Dakota. Ingredients for these overnight storms, should they
develop, to be efficient rainmakers are forecast to be in place.
But training would still be required for there to be any risk of
excessive rain/localized flash flooding. This remains a low
probability outcome at this time.

The thunderstorm forecast for Saturday is highly uncertain, and will
likely remain so until the day of given the uncertainty of how
today/tonight will evolve and influence the environment for
tomorrow. There is little to no doubt that a high CAPE/high shear
environment will be in place from far south central to southeast
North Dakota Saturday afternoon and evening. However, a) there might
not be enough forcing to initiate/sustain convection, and b) mid
level capping could once again suppress or prevent deep moist
convection. Most CAMs do not simulate any strong to severe
convection in North Dakota through Saturday evening, although a few
bring some elevated convection into the southern James River Valley
late Saturday night. We will message a potential for isolated strong
to severe storms on Saturday from south central into eastern North
Dakota, but the probability of severe convection on Saturday is much
lower than today.

The favored synoptic pattern for next week looks slightly more
progressive than it did at this time yesterday. A shortwave digging
into the Upper Midwest has shifted slightly westward in more recent
ensemble runs, and the advertised northwest flow pattern looks
shorter in duration, with the upstream western CONUS ridge possibly
shifting into the Plains and flattening through the second half of
the week. NBM forecast parameters have not greatly shifted though,
which makes sense as these are still emerging ensemble trends. Highs
are still forecast to generally be in the mid 70s to upper 80s each
day, and the NBM deterministic output still appears closer to the
25th percentile of the distribution. There is increasing confidence
in a a period of dry weather for most of the state Sunday into
Tuesday, with low chances for showers and storms returning to the
forecast late Tuesday followed by daily medium chances thereafter.
The probability of severe weather next week remains low at this
time.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1205 PM CDT Fri Jun 27 2025

MVFR-IFR ceilings will persist at KJMS into the early portions
of the 18Z TAF period, otherwise VFR conditions are expected
this afternoon. Late this afternoon and early evening, severe
thunderstorms could develop from around KXWA to KMOT to KBIS and
track southeast through the evening. Large hail will be
possible with any storm that develops during the late afternoon
and early evening. Strong wind gusts and at least IFR visibility
reductions from heavy rain can also be expected with any storm.
Aside from thunderstorms, winds will primarily become southerly
around 10 kts today, with direction turning westerly in western
North Dakota.

&&

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

&&

$$

UPDATE...TWH
DISCUSSION...Hollan
AVIATION...TWH