972
FXUS63 KBIS 150147
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
847 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 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