883
FXUS63 KBIS 241731
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1231 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- There is a low probability for isolated severe storms this
  afternoon and evening from the Highway 83 corridor to the
  Turtle Mountains and James River Valley. Potential hazards
  include hail up to golf ball size and damaging winds up to 70
  mph.

- Warm and humid across the eastern half of the state today,
  then slightly cooler and mostly dry Tuesday and Wednesday.

- Medium to high chances for showers and thunderstorms Thursday
  afternoon through Thursday night.

&&

.UPDATE...
Issued at 1225 PM CDT Mon Jun 24 2024

Minimal changes were needed with this update. The precipitation
was quicker to exit than anticipated, so we removed PoPs from
our area for the next hour. Cloud coverage has also decreased
quite a bit. Otherwise, just blended the current observations
into the forecast. The SPC has also removed us from the Slight
Risk in the east, and trimmed back the Marginal Risk across
central North Dakota, which is in line with our current thinking
that the severe potential is decreasing with each subsequent
forecast. The potential is still there, just much lower than
before.

.UPDATE...
Issued at 846 AM CDT Mon Jun 24 2024

Showers and thunderstorms have almost completely exited the
area, with a few lingering thunderstorms present in Foster,
LaMoure, and Dickey counties. There is still a very low chance
that any of these may become strong to severe, but the
likelihood of that being the case continues to decrease, given
how widespread the cloud coverage and convection earlier this
morning was. Otherwise, the forecast remains on track, with a
few small adjustments being made to the cloud coverage.

.UPDATE...
Issued at 522 AM CDT Mon Jun 24 2024

The Severe Thunderstorm Watch for north central North Dakota was
allowed to expire at 5 AM CDT. The intensity of convection across
all of central North Dakota has trended notably downward over the
past hour, but a few stronger storms remain possible. The highest
probability for a stronger storm through mid morning remains across
north central North Dakota, where shear is strongest. We expected
the large complex of showers and storms to continue propagating
eastward through the morning.

&&

.DISCUSSION...
Issued at 321 AM CDT Mon Jun 24 2024

Shortwave energy riding over the top of a mid to upper level ridge
axis has sparked areas of showers and thunderstorms from eastern
Montana into western and central North Dakota early this morning,
with forcing being aided by a low level jet with strong moisture
transport. The strongest convection has been focused along the
Canadian border in Burke, Renville, and Bottineau Counties. Two long-
lived supercells have now weakened and transitioned to more of a
compact linear mode, but another supercell upstream has entered
northeast Burke County as of 3 AM CDT. Stronger storms were also
previously located along the Missouri River in northeast Montana,
with hail up to ping pong ball size at Wolf Point earlier in the
night. That convection also weakened as it moved into northwest
North Dakota, but small hail and gusty winds remain possible.
Finally, scattered showers with occasional lightning have blossomed
within a low level warm air advection zone across southwest North
Dakota in a much weaker effective shear environment. There is medium
to high forecast confidence that showers and storms will persist
moving east across the state this morning into the afternoon, but
low confidence on intensity. Through this morning, the strongest
shear remains farther north.

Convective evolution later this afternoon is far more uncertain,
with CAMs already having struggled with overnight activity. The air
mass downstream of an eastward advancing cold front/dryline will
become very unstable this afternoon, with surface dewpoints
increasing to the 70s and CAPE approaching 4000-5000 J/kg in a
moderately sheared environment. Strong capping above the boundary
layer and the unknown convective evolution this morning contribute
to the uncertainty of convection this afternoon, and the best
forcing through all atmospheric layers is not lined up spatially. On
one end of the forecast spectrum, a few severe storms could develop
this afternoon east of Highway 83, which could be new convective
initiation or re-intensification of lingering convection from
earlier in the day. This outcome has been offered in consecutive
runs of the NAMnest, for example. On the other end of the forecast
spectrum, morning convection could exit the forecast area by the
afternoon, with no additional development for the rest of the day.

The aforementioned cold front/dryline is forecast to cross the state
from west to east through the day. The eastern half of the state
will have a warm and muggy afternoon, with highs in the mid 80s to
lower 90s and afternoon heat indices pushing the mid 90s in the
southern James River Valley. It will be only slightly cooler but far
less humid to the west. Later tonight, a mid level shortwave riding
over a low level baroclinic zone could bring some scattered showers
and thunderstorms along the South Dakota border. Any storms should
remain well below severe limits due to negligible bouyancy.

A transition to cyclonic northwest flow is expected on Tuesday, with
surface ridging building from the southern Canadian Rockies into the
northern High Plains. A few afternoon and evening showers are
possible along the Canadian border, with breezy conditions. On
Wednesday, northwest flow aloft transitions to anticyclonic with the
broad surface high becoming more focused over the region. This
should result in a very quiet weather day. Highs on Tuesday and
Wednesday will generally range from the 70s north to 80s south.

There continues to be strong model consensus for an upper level low
landing on the Pacific Northwest Wednesday night, crossing the
Northern Rockies on Thursday and reaching the Northern Plains on
Friday. NBM PoPs begin to increase Wednesday night as a preceding
lee trough intercepts the nocturnal low level jet. Then
deterministic global models continue to indicate the potential for
widespread showers and storms later Thursday through Friday, with
NBM PoPs as high as 90 percent. CSU machine learning severe
probabilities have increased over the past 24 hours, and a quick
look at the CAPE/shear parameter space in deterministic guidance
suggests all severe hazards could be in play. Heavier rainfall could
also be a concern with this system, with NAEFS/ECMWF showing 90th-
95th climatological percentile values of precipitable water. Warm
and/or humid conditions are possible on Thursday, but below normal
temperatures are favored on Friday and Saturday following the
passage of the trough, with the NBM now advertising highs as cool as
the mid and upper 60s.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1225 PM CDT Mon Jun 24 2024

VFR conditions are present across the area, and will prevail
through the TAF period. Some isolated low clouds are forming in
a few areas as well, but should dissipate shortly. Winds are
not being resolved well by the models due to the residual
boundaries left behind by the convection this morning, but by
later this afternoon, they will mostly be out of the northwest
around 10 to 15 kts, before decreasing to mostly light and
variable into the overnight hours.

&&

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

&&

$$

UPDATE...Besson
DISCUSSION...Hollan
AVIATION...Besson