Garrison, North Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

775
FXUS63 KBIS 261745
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1245 PM CDT Thu Jun 26 2025

.KEY MESSAGES...

- An isolated strong to severe thunderstorm could impact far
  northwest North Dakota this evening. Expected hazards include
  hail as large as quarters and damaging wind gusts as high as
  60 mph.

- Patchy fog is possible Friday morning over south central North
  Dakota into the James River Valley.

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

- Near to slightly above average high temperatures in the 80s
  are forecast Friday through next week. Friday will also be
  humid for all but far western North Dakota.

&&

.UPDATE...
Issued at 1245 PM CDT Thu Jun 26 2025

While fog has lifted by the time of this mid day update, low
stratus lingers over much of western and central North Dakota.
Some erosion of this stratus layer is evident on satellite
imagery across the west, though this is is somewhat slow going.
With this in mind, have slightly lowered temperatures across
central North Dakota this afternoon. Otherwise, for forecast
updates, have opted to add patchy fog across portions of south
central North Dakota into the James River Valley early tonight
through the mid morning hours Friday. An interrogation of BUFKIT
model soundings during this period leads me to expect this fog
to be somewhat shallow, and should lift pretty readily after
dawn. No other adjustments to the forecast were performed with
this update.

UPDATE
Issued at 950 AM CDT Thu Jun 26 2025

Low stratus and some stubborn patchy fog can be found over much
of the forecast area at the time of this morning update.
Visibility has gradually improved over the last few hours,
especially in the southwest where it had fallen as low as 1/2
mile or less at times. Fog is expected to generally lift across
over the next hour or so. Low stratus has begun to move eastward
this morning, and will continue to do so through the late
morning and early afternoon. There may be some need to lower
high temperatures across the James River Valley this afternoon
where the residence time of this low stratus is expected to be
the longest, though will hold off until the mid day update for
now. Overall, the forecast remains on track.

UPDATE Issued at 653 AM CDT Thu Jun 26 2025

Widespread low stratus producing drizzle, mist, and fog
continues to plague most of western and central North Dakota
early this morning. Recent observations show the fog is becoming
more dense in southwest parts of the state. Will continue to
monitor for potential need for enhanced fog messaging.
Meanwhile, radar shows light showers developing and moving into
southeast parts of our forecast area, east of Highway 83 and
along and south of Interstate 94. PoPs have been updated through
the morning to reflect observed trends.

&&

.DISCUSSION...
Issued at 432 AM CDT Thu Jun 26 2025

The Northern Plains are under a broad southwesterly upper level flow
pattern early this morning, and are forecast to remain so through at
least Saturday. RAP analysis shows a weak 700-500 mb cyclonic
circulation over North Dakota with a moist easterly flow underneath
driven by broad high pressure over eastern Canada. This has promoted
widespread low stratus across most of western and central North
Dakota, with observed northwest expansion still ongoing. Drizzle and
mist have been common underneath the low stratus, and a few webcams
have suggested fog, but not dense.

Most of western and central North Dakota will remain free from
showers and thunderstorms through this afternoon. The aforementioned
mid level cyclonic circulation is forecast to deepen over the
central Dakotas this morning, which could bring some light showers
into the James River Valley through mid afternoon. The low clouds
and light drizzle/mist/fog are likely to scatter/lift in a northwest
to southeast fashion through the afternoon behind the deepening wave
as low level flow turns more southerly. The timing of the clearing
of clouds will highly influence the high temperature outcome for
today. Our current expectations range from the lower and mid 80s
along the Montana border to around 70 in the James River Valley,
where cloud cover could hold on into the evening.

Isolated to widely scattered convection is forecast to initiate
along a lee trough across eastern Montana late this afternoon, with
forcing also supported by mid level height falls with upstream
cyclonic vorticity maxima embedded in the main flow. A few of these
storms could move into far western parts of the state this evening,
with higher probabilities northwest compared to southwest on account
of stronger lift from DCVA and WAA. The atmosphere is forecast to
only be marginally supportive of lower-end severe convection, with
MUCAPE around 1000 J/kg and 0-6 km bulk shear increasing from around
30 to 40 kts through the evening in the northwest. There is forecast
uncertainty in storm mode, with vector orientation to the boundary
ranging from nearly perpendicular for deep layer shear to nearly
parallel for anvil level SR flow. This uncertainty is reflected in
the 00Z suite of CAMs, whose reflectivity fields depict a mixed/
cluster mode. Given this uncertainty and the lower-end CAPE/shear
parameter space, we will continue to advertise baseline severe
hazards of quarter size hail and 60 mph gusts in far northwest North
Dakota this evening. A few clusters of showers and isolated
thunderstorms could persist across northwest and spread into north
central North Dakota through tonight, but the the threat of stronger
storms should end near or shortly after midnight and remain confined
to the far northwest.

A somewhat continuous stream of mid level shortwave energy embedded
in the southwest flow aloft is forecast over the region Friday, with
surface/low-level lee troughing shifting into western North Dakota.
The air mass downstream of the lee trough is forecast to contain
surface dewpoints in the 60s combining with 80s high temperatures to
yield SBCAPE around 2000 to 3000 J/kg. The lack of a strong forcing
mechanism and favored presence of mid level capping introduces
uncertainty to the convective initiation forecast. Still think the
most likely outcome is for enough low level convergence combined
with weak mid level height falls sufficiently eroding CIN to allow
at least a few thunderstorms to develop across central North Dakota
during the late afternoon/early evening hours on Friday. There is
larger forecast spread in the amount of deep layer shear, ranging
from as little as 30 kts to as high as 50 kts, but most
deterministic models and ensemble systems do show shear increasing
over time. The lack of strong forcing and deep layer shear/wind
vector orientation to the boundary strongly point toward an initial
discrete supercell mode, with possible upscale growth later in the
evening primarily driven by cold pool propagation if the coverage of
discrete supercells ends up being more scattered than isolated. The
expected storm mode combined with the higher ends of the CAPE/shear
forecast distribution lead to very large hail (up to tennis ball
size) being the primary expected hazard, but clustering storms later
in the evening could have access to waning, but sufficient DCAPE and
strong 0-3 km shear to maintain a damaging wind threat (gusts as
high as 70 mph). The risk for tornadoes is more uncertain. The 03Z
RAP in particular is quite bullish on a favorable tornado setup,
including STP in the 1 to 3 range and model hodographs favoring
strong streamwise vorticity. However, the 00Z HREF only has a low to
medium probability of STP exceeding 1 by the end of its run early
Friday evening, and its hodographs are not as looped or concave in
the lowest 1-2 km. Given this, and the lower confidence in storm
coverage, we will continue to advertise a tornado or two possible.
But a reasonable worst-case scenario could be any supercell that
develops carrying a tornado risk.

Most of the storms that develop Friday afternoon and evening should
push off to the south and east by late Friday night. However, an
intensify low level jet could lead to convective maintenance or
perhaps even new development. Should this occur, training convection
within a warm and moist deep layer could introduce an excessive
rainfall risk. Low chances for thunderstorms remain in the forecast
on Saturday under continued southwest flow aloft and with a NE-SW
frontal boundary stalling across the region. The Storm Prediction
Center has introduced a Marginal Risk (level 1 out of 5) for severe
storms across south central and eastern North Dakota on Saturday,
but any convection on Saturday could be greatly influenced by how
storms evolve in the preceding 12 to 24 hours.

Longer range ensembles favor a trough digging into the Great Lakes
region early next week as an upper ridge becomes amplified over the
western CONUS, placing the Northern Plains in a prevailing northwest
flow regime. Temperatures are favored to be near to slightly above
average through next week, for which late June is highs in the lower
80s. Ensembles favor a period of drier weather to the start the
week, with shower and thunderstorm chances increasing back to medium
levels by mid week. At this time, GEFS-based machine learning
guidance does not contain any strong signals for severe storms for
the first half of next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1245 PM CDT Thu Jun 26 2025

Low stratus is causing MVFR to IFR ceilings across the forecast
area at the time of this mid day update. As this stratus deck
continues to move eastward through the afternoon, ceilings are
expected to broadly improve to VFR conditions from west to east.
KJMS may remain under MVFR ceilings through the early evening
hours. Later this evening, chances for showers and thunderstorms
are expected to increase across northwestern North Dakota,
including around the KXWA terminal. Some of these storms may
become strong to severe, with large hail up to quarters (1 inch)
in size and wind gusts up to 60 MPH. These thunderstorms
expected to generally diminishing through the late evening into
the early overnight period, though scattered showers may linger
across the north. Confidence is too low to include mentions of
showers or thunderstorms anywhere except for KXWA at this time.
Friday morning, patchy fog is possible across portions of south
central North Dakota into the James River Valley. Have included
visibility reductions at KJMS with this update. Currently, this
fog is expected to be somewhat shallow, and should readily lift
by the mid morning hours. Otherwise, Light east to southeasterly
winds are anticipated throughout the TAF period.

&&

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

&&

$$

UPDATE...Adam/Hollan
DISCUSSION...Hollan
AVIATION...Adam