641
FXUS63 KBIS 171441
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
941 AM CDT Sat Aug 17 2024

.KEY MESSAGES...

- Areas of near surface smoke from distant wildfires will
  continue through much of the day, but should start to diminish
  from east to west in the afternoon and into the evening.

- Areas of dense fog will be possible across portions of western
  and much of central North Dakota through the morning hours. A
  Dense Fog Advisory has been issued.

- Expect low to medium chances (20 to 40 percent) for showers
  and thunderstorms across the west this morning. An isolated
  thunderstorm or two will be possible northwest or north
  central this afternoon and evening, possibly strong.

- Low to medium chances (20 to 50 percent) for showers and
  thunderstorms return to the forecast Monday afternoon through
  Tuesday. A few strong storms will be possible.

&&

.UPDATE...
Issued at 938 AM CDT Sat Aug 17 2024

Fog continues across western and central North Dakota.
Visibilityis starting to improve with some areas still down to
quarter of a mile. Showers and Thunderstorms are moving across
the southwest and are quickly diminishing in strength. Adjusted
PoPs and weather grids to match the current conditions.

UPDATE
Issued at 617 AM CDT Sat Aug 17 2024

Crosby visibility has remained below a quarter mile and traffic
cams near Mott suggest that visibility has really tanked there
as well. Thus, we decided to tack on Divide (mainly the eastern
portion of the county) and Hettinger counties to the Dense Fog
Advisory. A few more radar echoes also continue to nudge in from
eastern Montana with some lightning strikes here and there. If
we were to see a strong storm or two this morning, it will
likely be across the southwest.

&&

.DISCUSSION...
Issued at 353 AM CDT Sat Aug 17 2024

The main story in the near term for western and central North Dakota
is lowered visibility from dense fog and/or near surface smoke from
distant wildfires. Automated observations and traffic webcams
suggest that areas of dense fog are starting to settle in across
portions of the west and much of the central, leading to visibility
values of a quarter mile or less in some locations. We decided to go
ahead and issue a Dense Fog Advisory for these areas as CAMs suggest
it should only become worse and more widespread through the early
morning hours. Complicating the fog threat is the addition of
reduced visibility from near surface smoke. The HRRR and RAP smoke
models suggest that near surface smoke will gradually diminish from
east to west through the day and into the evening. However, it
remains unclear how long smoke aloft may stick around. Both of these
threats could make for hazardous driving conditions out on the roads
this morning.

At the mid to upper levels, a closed low continues to spin over the
Great Lakes region with a ridge draped over the northern Plains. A
weak shortwave was noted on water vapor satellite imagery over
eastern Montana near the slightly flattened mid level ridge axis,
bringing modest height falls to eastern Montana and western North
Dakota. This modest forcing will maintain low to medium chances (20
to 40 percent) for showers and thunderstorms across the west through
much of the morning. This activity will struggle to organize in
our area as the ridge starts to build again and heights rise
across the west. Rising heights will limit convection most of
the afternoon and evening, but a couple of the CAMs suggest a
conditional chance for a thunderstorm or two. If a storm can get
going across the far west, forecast soundings suggest it would
have around 500 to 1000 J/kg of MLCAPE and 45 to 55 knots of
deep layer shear to possibly work with. Thus, while convection
is uncertain given rising heights, if a storm can form it would
have the potential to become strong to marginally severe.
Precipitation chances will then diminish through the evening.
Highs today will range from the mid 70s northeast to the mid 80s
southwest and lows tonight will mainly be in the mid 50s to the
lower 60s.

Sunday will be a bit warmer and a bit drier with highs mainly in the
80s (upper 80s west). The thunderstorm environment will be fairly
similar to today across the southwest with a little less shear.
However, we will see rising heights through the day as the ridge
amplifies overhead with very little in the way of upper level
forcing. Thus, convective initiation appears unlikely for now.

Better chances for showers and storms (20 to 50 percent) may come
Monday afternoon through Tuesday as a stronger wave starts to move
in, flattening the ridge. Highs on Monday will range from the lower
80s east to the lower 90s west. We should also see widespread
dewpoints in the the low to mid 60s which should lead to around 2000
J/kg of MLCAPE across the west. Deep layer shear will be fairly weak
through the afternoon around 20 to 25 knots, but we may see that
increase to around 30 to 35 knots around and after 00z. Given said
environment, a few isolated strong to marginally severe storms will
be possible west. The story may be very similar on Tuesday depending
on wave timing, but maybe a bit further into the central and east.
Storms should move out to the east by Tuesday evening, but most
solutions keep us either in near zonal or gradual southwest flow
aloft through the rest of the week. Thus, a few weak waves may bring
low precipitation chances to the area at times mid to late week.

Highs on Tuesday will be similar to Monday, ranging from the upper
70s and lower 80s east to the upper 80s and lower 90s west.
Wednesday may be the warmest day of the week with highs forecast to
range from the mid 80s east to the low to mid 90s west. Highs then
back off into the upper 70s to upper 80s Thursday and Friday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 617 AM CDT Sat Aug 17 2024

Areas of dense fog will continue across portions of western and
most of central North Dakota through at least mid morning. This
will lead to LIFR to MVFR visibilities before fog diminishes in
the 14z to 16z time frame. After fog lifts, we could still see
some MVFR visibilities due to near surface smoke from distant
wildfires, but this should also be diminishing through the day.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM CDT /10 AM MDT/ this morning
for NDZ001>004-009>013-017>023-033>036-041-042-044>047-050.

&&

$$

UPDATE...Johnson
DISCUSSION...ZH
AVIATION...ZH