372
FXUS63 KBIS 100527
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1227 AM CDT Wed Jul 10 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
  at various times from Thursday evening through the weekend.

&&

.UPDATE...
Issued at 1221 AM CDT Wed Jul 10 2024

Storms have moved out of the county warning area. Smoke
continues to settle as a nocturnal inversion sets up, however
visibility remains above 6 miles across sites with smoke. No
other updates are need at this time.

UPDATE
Issued at 943 PM CDT Tue Jul 9 2024

The shower and thunderstorm activity has mostly ceased across
the area, with a few showers lingering around in far eastern
LaMoure and Dickey counties. The main update was just adjusting
the PoPs and sky cover to better reflect current trends.
Otherwise, the forecast remains on track.

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 /06Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1226 AM CDT Wed Jul 10 2024

VFR conditions will persist at all terminals through the latest
TAF cycle. FU will settle across the central half of the state
impacting KJMS, KMOT, and KBIS before sunrise. FU should
disperse later in the afternoon increasing visibility. Light
south to southeasterly winds will continue today.

&&

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

&&

$$

UPDATE...Johnson
DISCUSSION...Hollan
AVIATION...Johnson