235
FXUS63 KBIS 150444
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1144 PM CDT Sun Jul 14 2024

.KEY MESSAGES...

- Isolated to scattered severe storms are expected tonight in
  parts of western and central North Dakota.

- Hail to the size of tennis balls and damaging wind gusts to 70
  mph remain the main hazards.

- Cooler weather returns to start the work week, with a modest
  warmup for the second part of the upcoming week.

&&

.UPDATE...
Issued at 1144 PM CDT Sun Jul 14 2024

We have expired the Severe Thunderstorm Watch for far western
North Dakota, and are allowing additional counties in western
and north central North Dakota to expire at midnight as planned.
With multiple ongoing severe thunderstorms, we have issued a new
Severe Thunderstorm Watch valid for much of south central and
southeast North Dakota, including the James River Valley. A few
counties have been included in both watches.

UPDATE
Issued at 1059 PM CDT Sun Jul 14 2024

** Mesoscale Discussion **

The risk of severe storms with large hail up to tennis ball size
and damaging winds up to 70 mph will continue over central ND
for several more hours, while expanding southeast with time.

At 0345 UTC, several supercells continue over north central ND
and into the Lake Sakakawea vicinity. Earlier it appeared that
the western-most storms were beginning to congeal into a more
linear structure, but those attempts have been slow to occur,
likely related to lingering midlevel capping that is allowing a
more discrete convective mode to persist. Gradual upscale growth
is still anticipated but a mix of supercells and more linear
structures may persist for several more hours. Surface analysis
has a low over Dunn County, and a broad warm frontal zone and
confluence zone marked by a subtle shift from southeast to more
easterly winds extends from that low east across Lake Sakakawea
and then angles toward Carrington and Jamestown. The low-level
moisture axis with dewpoints in the middle 60s F also extends
along that zone, and the gradual southeast movement of existing
supercells suggests the greatest severe-storm risk will be near
that zone the next several hours. If upscale growth can occur,
the environment favors significant-severe winds, but aside from
that, the CAPE-shear setting continues to favor very large hail
owing to effective shear on the order of 50-60 kt with discrete
storm structures. The southeast extent of the severe storm risk
overnight is somewhat uncertain, owing to midlevel capping south
of I-94, and will likely be dependent on whether or not a more
linear/cluster mode and cold pool takes shape or not. If a more
linear structure develops, then a more southeast motion could
exist into the axis of greater bouyancy since forced ascent from
a cold pool could overcome capping. However, if a somewhat more
mixed supercell/cluster modes persist, then the highest chance
of severe storms will likely follow more closely to the warm
frontal zone extending from Garrison toward Harvey, Carrington,
and Jamestown and vicinity.

CJS

UPDATE
Issued at 943 PM CDT Sun Jul 14 2024

Main change with this update was to freshen up POPs in line with
current radar trends. Two broad areas of severe convection
continue late this evening: one over portions of northwest North
Dakota, focused in Mountrail County, and one in the north
central, focused in McHenry and Pierce Counties. The mesoscale
discussion has more technical details on our thinking for the
next few hours. We are watching for the potential of the storms
in northwest North Dakota to transition to a linear storm mode,
which will be dependent on the development of a sufficient cold
pool.

UPDATE
Issued at 846 PM CDT Sun Jul 14 2024

** Mesoscale Discussion **

The risk of severe storms through 11 pm CDT will be greatest in
parts of central and northwestern ND, with the main threat over
the next few hours in the form of large to very large hail, up
to tennis ball size.

As of 0130 UTC, supercells persist over north central ND from
Bottineau into McHenry and Pierce Counties, despite storm-scale
outflow in the wake of leading supercells. The environment has
large elevated bouyancy and strong deep-layer shear, and that
is apparently compensating for any low-level stability in the
wake of the leading storms. This setting is unlikely to change
in the near term, so a large to very large hail risk is expected
to continue with southeast-moving supercells in that area.

Meanwhile, storms have gradually intensified in northwestern ND
in the vicinity of Williston. This area is located near the nose
of the low-level thermal ridge, and near a confluence axis in
the low-level wind fields from more southerly to southeast flow
that extends from roughly Williston toward Garrison. Low-level
moisture increases downstream of these storms as well, with
surface dewpoints of 65-70 F. We therefore expect these storms
to intensify into one or more supercells with potential large
hail up to about tennis ball size given MLCAPE of 2000-3000 J/kg
and effective-layer shear of 50-60 kt. Low-level hodographs
possess sufficient curvature to favor the right-moving
supercells (with left-splits likely to weaken), though 0-1-km
SRH is only around 100 m2/s2. In time, upscale growth could
occur with these storms, resulting in an increasing damaging
wind threat, but that is less-certain given downstream capping
on the 00 UTC KBIS sounding, which could favor persistence of a
more discrete convective mode a bit longer than otherwise may be
expected. That capping at the base of the elevated mixed layer
has also resulted in only slow intensification to the updrafts
northwest of Bismarck in Oliver/Morton Counties, and suggests
the odds of supercell development in the near term as far south
as the I-94 corridor is only low to medium.

CJS

UPDATE
Issued at 650 PM CDT Sun Jul 14 2024

Surface low is analyzed in southeast Montana this evening, with
a broad cu field and some weak radar returns continuing to
develop north and east of the center, in northeast Montana and
southwest North Dakota. These will be the areas to watch in the
next couple of hours with a favorable synoptic environment in
place, with SPC mesoanalysis showing 50-60 knots of bulk shear
and generally uncapped 1500-2500 J/kg of MLCAPE, in line with an
upper jet streak. The other area of concern is in north central
North Dakota into the southern Canadian Prairies, where the
strongest storms of the day have been so far along a wind shift.
Made some adjustments to POPs based on latest NBM and current
radar trends otherwise going forecast looks good for now.

UPDATE
Issued at 510 PM CDT Sun Jul 14 2024

Quick update for Severe Thunderstorm Watch issuance for
northwest and north central North Dakota until midnight tonight.
There is one supercell just across the International Border,
north of Renville County, that will be crossing into North
Dakota relatively soon. Otherwise main focus is on agitated cu
field in the Glasgow area, with some radar returns showing up in
far northeast Montana that will be moving into North Dakota
through the evening.

&&

.DISCUSSION...
Issued at 216 PM CDT Sun Jul 14 2024

Current surface analysis places low over northeast Wyoming with
inverted trough stretching up to the north into eastern Montana.
Upper level analysis places broad high over the Four Corners
region with low over far northern Manitoba. West-northwesterly
flow remains over our area, which remains active with a series
of short waves passing through. Initial wave now passing
through northwestern North Dakota, with the secondary one over
southwest Saskatchewan/northern Montana. Yet another wave noted
upstream from there. Over our area, temperatures over most
locations have climbed into the 80s knocking on the lower 90s.

For this afternoon into tonight, the threat of severe weather
remains in place but as has been going on for quite a while,
the timing remains our fly in the ointment. A diverse group of
solutions are being shown by latest CAMs, with some initiating
convection with the initial wave moving through the area, while
others are holding off until later. Some of the CAMs indicate
convection developing with the initial wave in the not to
distant future, but a quick look at our 19Z special sounding has
a pretty pronounced cap over us, thus confidence in this
occurring is diminishing, so now the best bet looks to be more
towards the evening hours.

Once convection does finally initiate, the potential is there
for it to become quite robust. Deep layer shear is notably
stronger than what we have had here the past few days, forecast
to be about 50 kts across the area by early evening. This will
combine with plenty of instability with MLCAPE values still
anticipated to be in the 1500 to 2500 J/Kg range, plenty ample
for severe convection. With the strong shear and ample
instability, will maintain the threats previously forecast of
tennis ball size hail and wind gusts to 70 mph. As for the
tornadic threat, with the inverted trough sliding east, possibly
closing off, enough lower level shear may be provided if a
storm passes over the right area, though this setup is not ideal
we cannot rule out a tornado or two if a discrete supercell
were to develop early in the event. Convection will slide to the
east/southeast through the evening/overnight hours.

By Monday morning short waves will be pushing off to the east,
but some showers/thunderstorms may linger over parts of
northwest North Dakota into the James River Valley primarily
during the morning hours. Upper flow does become a bit cyclonic
in the afternoon as upper low with various waves swinging around
it drops southward along the Manitoba/Ontario border, so can
not rule out an increase in cloud cover in the afternoon, along
with a few stray very light showers in the afternoon/early
evening with additional activity overnight. Temperatures will
be notably cooler as the north/northwesterly flow pulls in a
cooler airmass, resulting in highs in the mid 70s to lower 80s.
Flow aloft remains modestly cyclonic on Tuesday, continuing low
chances for showers/weak storms.

Stout ridge builds to our west and remains in place for the
middle/end to the week. This will result in a modest warming trend
returning temperatures to the 80s to around around 90 by Thursday
continuing into the weekend. A few weak waves passing over the ridge
will bring some low precipitation chances to the area towards the
weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 650 PM CDT Sun Jul 14 2024

Isolated to scattered thunderstorms are likely across much of
western and central North Dakota through this evening and into
tonight, but there is low confidence in any specific timing and
location. Expect development to impact most TAF sites at some
point, with the thunderstorm potential ending from west to east
this evening and overnight. MVFR to potentially IFR conditions,
as well as gusty and erratic winds, are possible in and around
any thunderstorms. Winds on Monday will be from the north-
northwest around 10 knots.

&&

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

&&

$$

UPDATE...CJS/Jones
DISCUSSION...JJS
AVIATION...Jones