286
FXUS63 KBIS 092343
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
643 PM CDT Tue Jul 9 2024

.KEY MESSAGES...

- Smoky skies are expected through Wednesday, with some near-
  surface smoke reducing visibility at times across central
  North Dakota.

- Hot and humid conditions are expected Thursday through Sunday,
  with highs mostly in the upper 80s to upper 90s.

- Low chances for showers and thunderstorms are in the forecast
  for today and at various times from Thursday evening through
  the weekend.

&&

.UPDATE...
Issued at 628 PM CDT Tue Jul 9 2024

As showers and thunderstorms continue across the James River
Valley, a few isolated showers may develop across the northwest
over the next few hours as well. A cluster of stronger storms
has since congealed into one cell and strengthened further,
which warranted a Severe Thunderstorm Warning in portions of
LaMoure, Logan, and Stutsman counties. Will continue to monitor
if any further development will be possible across this area,
but our current thinking is that this will likely be it in terms
of severe development. We also had a small cell with a few
lightning strikes pass near Williston, so our main change for
this update was adding in some PoPs to the northwest for the
next few hours. Diurnal cumulus in eastern Montana has also
begun to move into the area up there, so just slightly boosted
cloud coverage in that area as well. Otherwise, the forecast
remains mostly on track.

&&

.DISCUSSION...
Issued at 235 PM CDT Tue Jul 9 2024

The Northern Plains still remain in a cyclonic northwest flow
pattern this afternoon, though the upstream ridge over the Rockies
is beginning to nudge closer. A shortwave trough is crossing the
eastern half of the state from north to south this afternoon, and
there is evidence of a meso-low centered between Bismarck and Harvey
from visible satellite trends and the analyzed surface wind field.
These features could help spark a few more sustained showers and
thunderstorms over the James River Valley and areas adjacent to the
west through the evening. More sporadic afternoon convection driven
by diurnal heating under the cyclonic flow is possible elsewhere,
but coverage away from the meso-low is forecast to be lower. A few
CAMs have been simulating a couple of strong thunderstorms with
the shortwave/meso-low in the James River Valley. While SBCAPE
is already analyzed around 2000 J/kg and 0-6 km shear could
increase to near 30 kts, model soundings show a thermal
inversion around 600 mb that was sampled by the 12Z BIS RAOB
that could provide some inhibition. Additionally, RAP non-
supercell tornado (NST) parameter projections are once again
highlighting a funnel cloud risk over the James River Valley,
and though this potential could be lower than previous days
given the slight bump in deep layer shear, the meso- low could
supply locally enhanced surface vorticity. On Wednesday, flow
aloft will turn more northerly and transition to more of an
anticyclonic regime over broad surface ridging. This should
finally give us a break from any afternoon showers or storms.
Highs both this afternoon and Wednesday are forecast in the 80s,
closer to 80 in the Turtle Mountains area and closer to 90 in
the southwest.

Despite the subtle shift in the synoptic pattern, trajectories will
remain favorable for smoke from Canadian wildfires to spread over
the region through at least Wednesday. Forecast confidence is higher
in smoke aloft than at the surface, and concentrations of both
should be greater over central North Dakota compared to farther
west. Tonight there looks to be a potential for a repeat of a
smoke/fog combination reducing visibility to around 3 to 6 miles, as
was observed this morning.

For Thursday through Sunday, an expansive heat dome/upper level high
pressure over the mountain states will push its northeast periphery
into the Northern Plains. The main story for us over this time
period is above normal temperatures, with NBM forecast highs in the
upper 80s to upper 90s most of these days at most locations, and
approaching 100 degrees in the southwest. Forecast dewpoints are
also consistently in the 60s, expect in the southwest, and approach
70 in eastern parts of our forecast area at times. While this
combination of heat and humidity is not unusual for this time of
year and this part of the country, this will be our first multi-day
stretch this summer. People that are highly sensitive to heat and
those who must spend time outdoors will want to take extra
precautions.

During this period of anomalous warmth, the Northern Plains could
also be in a favorable track for ridge riding shortwaves embedded in
stronger upper jet flow. This would lead to an increased risk of
thunderstorms at times, with at least some potential for severe
weather given the stronger flow aloft and warm/moist boundary layer.
CSU machine learning guidance has been consistently painting low
severe probabilities over much of the state Friday through Sunday.
While forecast timing and to a greater extent spatial details of
convection remain low at this time range, the first potential is
consolidating on Thursday evening across the western half of the
state ahead of a lee surface trough and upstream mid level impulse,
although a capping inversion could play a role in suppressing
convective development and strength. It is interesting to note that
subsequent time periods with mentionable NBM PoPs are mostly during
the evening and overnight despite there being no strong model signal
for a persistent nocturnal low level jet.

Early next week, ensemble spread greatly increases on account of
uncertainties in the evolution of troughing digging into the Great
Lakes region. There is a distinct lowering in the NBM high
temperature distribution next week, but mean values are still near
mid-July averages of mid 80s.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 628 PM CDT Tue Jul 9 2024

VFR conditions are present across all terminals, and will likely
prevail through the TAF period. Some isolated storms have formed
in the James River Valley, which may briefly bring about reduced
visibilities at KJMS should any of them pass over the airport.
Given the uncertainty in exact location of storm development,
only vicinity thunderstorms have been added for the next 3
hours. Some showers may also be possible across the far
northwest, with vicinity showers at KXWA for the next 3 hours as
well. Reduced visibilities to MVFR conditions due to a
combination of fog and near surface smoke may occur across
central and eastern North Dakota early Wednesday morning,
affecting KBIS, KJMS, and KMOT. Winds will decrease to light and
variable over the next few hours, remaining this way through the
rest of the TAF period.

&&

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

&&

$$

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