995
FXUS63 KBIS 301440
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
940 AM CDT Sun Jun 30 2024

.KEY MESSAGES...

- Isolated to scattered strong to severe thunderstorms are
  possible tonight, with up to a Level 2 of 5 risk. The main
  hazards are hail up to quarter size, and wind gusts up to 60
  mph.

- Breezy to windy conditions are expected today, especially
  southwest.

- There is a Level 2 of 5 risk for severe thunderstorms Monday
  in southern North Dakota, and a Level 1 of 5 risk for much of
  the rest of the area. The main hazards are hail up to half
  dollar size and wind gusts up to 60 mph.

&&

.UPDATE...
Issued at 940 AM CDT Sun Jun 30 2024

No major changes were needed with this update. A swath of
midlevel clouds with bases around 15k feet continue moving
through the state, covering areas south and west of the Missouri
River mid-morning. Scattered radar returns have been persisting
in this area, but with such high cloud bases our assumption is
that no precipitation is making it to the ground, and will
continue the dry forecast through today for now. The only other
thing to monitor is any additional development in northern South
Dakota that would potentially move into our far south central
and southeast later this morning.

UPDATE
Issued at 649 AM CDT Sun Jun 30 2024

Only minor changes were made with this update to blend observed
trends into this morning`s forecast. Patchy and shallow ground
fog is observed in satellite and web cameras in northwestern ND
and in the Glen Ullin/Mott areas, but that will dissipate with
diurnal heating in the next 1 to 2 hours. Otherwise, midlevel
clouds continue advancing into southwestern ND in association
with midlevel warm air advection, and a few radar echoes have
been present with this activity, but the high-based nature and
lack of more notable radar reflectivities mean we have kept the
forecast dry today for now. That will need monitoring though in
case low precipitation chances are needed in the south today.

&&

.DISCUSSION...
Issued at 402 AM CDT Sun Jun 30 2024

Early this morning surface high pressure is centered across the
eastern Dakotas, and is beginning to shift eastward while broad
surface low pressure deepens over the Northern Rockies region.
The result is increasing southeasterly low-level flow over the
High Plains downstream of an upper-level trough moving across
the Pacific northwest. Overnight IR satellite imagery reveals
a band of cooler cloud tops aloft associated with a shortwave
trough in eastern WA/OR, which will be a feature of interest
for our convective potential tonight.

For today, midlevel warm air advection will become pronounced
as southeast flow increases. This warm advection pattern has
already been manifest as a midlevel cloud deck and evidence of
high-based sprinkles or showers in central MT overnight, and
00 UTC guidance suggests midlevel saturation in the developing
warm air advection regime aloft will lead to midlevel clouds
crossing southwestern and south central ND today. There is a
very low chance of a shower with this setting, but confidence
in that was not high enough to include a mention in the forecast.
Otherwise, increasing winds will be the main story of the day
as the surface pressure gradient tightens, with southeast winds
increasing to 20 to 30 mph by afternoon over most of western and
central ND. Winds will be strongest in southwestern ND where
the surface pressure gradient will be strongest, but forecast
soundings suggest peak speeds at the top of the mixed layer will
only be around 30 kt, and thus forecast gusts will likely fall
short of Wind Advisory criteria. Moreover, ensemble guidance
including the ECMWF EFI all suggests the probability of advisory
criteria winds is less than 50 percent, so we held off on a
headline. Highs will be warmer today, ranging from near 70 in
east central ND to the upper 70s in southwestern ND.

Tonight the main concern will be potential thunderstorms, which
are expected to develop over the higher terrain of central MT
today as the aforementioned shortwave trough reaches that area.
The low-level jet will increase significantly downstream of that
shortwave trough tonight, with 40-50 kt speeds centered on the
850 mb level over much of western and central ND. Steep midlevel
lapse rates will exist, all of which favors convection. However,
low-level moisture return will be immature owing to the primary
low- and midlevel frontal zone that marks the boundary between
a recycled continental polar moisture profile and the rich
maritime moisture regime initially being displaced well south,
along the Kansas/Oklahoma border. Upstream observations at this
writing accordingly have surface dewpoints only in the 50s F as
far south as Kansas. This seasonably-tempered moisture return,
combined with a comparatively-warm elevated mixed layer noted on
00 UTC Salt Lake City and Riverton soundings, is apt to yield
significant inhibition/capping across western and central ND
tonight. Forecast soundings call for 1000-1500 J/kg of MUCAPE
for parcels originating in the 850 to 700 mb layer tonight, but
with MUCIN generally larger than -75 J/kg. Thus, while we expect
intense convection in eastern MT by this evening in a hotter,
more deeply-mixed and less capped environment, there are medium
to high odds that storms will weaken as they move into western
ND after sunset. Nonetheless, a risk of damaging winds (up to 60
mph) and large hail (up to quarters) exists, conditional on the
Montana convection developing sufficiently-deep cold pools and/or
shear-related organization to sustain itself into the
increasingly-capped air mass for some length of time into North
Dakota tonight. Even if the intensity of storms wanes, the
background environment will favor elevated showers and storms
progressing eastward tonight, as most CAMs and global ensembles
suggest, supporting 50 to 80 percent chances of precipitation
tonight, highest in northwestern ND.

Interestingly, by late tonight and Monday morning, the return of
richer low-level moisture could become sufficiently-deep enough
for parcels originating around the 850 mb layer to have reduced
CIN. If the ascent associated with the passing shortwave trough
and/or the weakening convection itself has not moved too far to
the east, outpacing the richer moisture return, then there will
be a window of opportunity for intensification of storms late
tonight into Monday morning, from approximately 09 to 15 UTC.
This risk is highly conditional, as it will be very sensitive to
the low- and midlevel moisture profiles that will determine
elevated parcel trajectories, and highly dependent on the timing
of ascent aloft and residual convection that could have upwind/
upshear re-intensification on its back side if moisture profiles
improve in time. This could result in a somewhat bi-modal timing
of tonight`s risk of severe storms, and is sufficiently high
for maintenance of the SPC Level 1 of 5 severe risk well into
central ND.

On Monday, another severe storm Risk (up to Level 2 of 5 from
SPC) will exist as a weak cool frontal boundary moves eastward
across western and into central ND during the day. Richer low-
level moisture marked by dewpoints in the 60s F is forecast to
reach the area, resulting in 1500-2000 J/kg of MLCAPE. However,
the boundary layer may still have residual capping, dependent
in part on how much stratus the low-level moisture advection
generates, and whether or not warming is offset by the richer
moisture. Early-day convection could also result in residual
cloud cover. This all results in a wide envelope of possible
outcomes, from little in the way of late-day storm development,
to upscale-growing clusters of storms. The 00 UTC NAM has an
especially cool and moist boundary layer with significant
capping, likely owing to a known PBL parameterization scheme
tendency, which suggests that its more lackluster convective
environment is likely a low-probability outcome. The 00 UTC
GEFS-based machine learning severe weather guidance increased
its signal for Monday, especially in central ND, and effective
layer wind shear of 30 to 40 kt supports multicellular to
supercellular storms if initiation occurs. However, parallel
alignment of shear profiles to the north-south-oriented surface
front, and hodographs that have largely straight-line geometry,
favor cluster-or upscale growing storms. Given the expected
mode, and background uncertainty in convective initiation, we
have chosen to message potential hazards of wind gusts up to 60
mph and hail up to half-dollar size, even though the CAPE-shear
setting itself favors potential hail sizes of 1 to 1.5 inches
or slightly greater. Any strong-severe storm risk will continue
into Monday evening, but gradually shift eastward.

Thereafter, persistent cyclonic flow aloft is still expected
to prevail through the week with low to medium precipitation
chances most days. Guidance continues to suggest a notable
shortwave trough could cross the region on Independence Day,
which is supporting 60 to 80 percent chances of showers and
storms that day. Machine-learning severe weather probabilities
are low through this period, though. Highs Tuesday through
Friday will generally be in the 70s to lower 80s F, with small
spread among NBM membership. By next weekend, roughly 60 percent
of global ensemble members favor some magnitude of upper-level
ridging developing, which could result in a step upward in
temperatures, and results in signs of a drier period setting
up. However, the other subset of ensemble members suggest lower
heights aloft with somewhat cooler (but still seasonable)
temperatures persisting longer.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 649 AM CDT Sun Jun 30 2024

VFR conditions will prevail today and into this evening across
western and central ND, though a band of midlevel clouds will
move across the area, especially in southern areas. Southeast
winds will increase today, with gusts of 25 to 35 kt (strongest
in the southwest including at KDIK). Those gusty winds will
continue into tonight. Low-level wind shear is forecast at KDIK
and KBIS for a few hours tonight as a 50 kt low-level wind max
develops as low as 1500 ft AGL. Showers and a few thunderstorms
are forecast to move out of Montana and into western ND in the
05-09 UTC time frame, and into central ND from 08-12 UTC.

&&

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

&&

$$

UPDATE...Jones
DISCUSSION...CJS
AVIATION...CJS