639
FXUS63 KBIS 140609
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
109 AM CDT Wed Aug 14 2024

.KEY MESSAGES...

- Low (20 to 40 percent) for showers with an occasional
  thunderstorm through tonight, followed by high chances (60 to
  80 percent) on Wednesday. A few storms could become strong.

- Torrential rainfall from slow moving thunderstorms could cause
  localized flash flooding on Wednesday. The highest risk is
  from south central North Dakota to the James River Valley.

- High temperatures are forecast in the 70s and 80s through
  early next week.

&&

.UPDATE...
Issued at 108 AM CDT Wed Aug 14 2024

At 1 AM CDT, shower activity was widely scattered across the James
and Sheyenne River Valley areas, with much more isolated activity
extending back west towards Lake Tschida. Occasional lightning has
been observed, but is far less frequent than earlier in the evening.
Current conditions and trends were blended into the forecast for
this update.

UPDATE
Issued at 1005 PM CDT Tue Aug 13 2024

Updated pops and sky cover late this evening based on the
latest radar and satellite analysis. Heavy rain has ended over
northern Morton and portions of western Burleigh counties. We
can`t completely rule out additional rain later tonight over
these areas, but at this time it looks like the next round of
potentially heavy rain will be Wednesday. Very high PWATs will
remain over the area, so any storms would have the potential to
produce very high rainfall rates.

UPDATE Issued at 709 PM CDT Tue Aug 13 2024

Thunderstorms continue over south central North Dakota. Strong
moisture flux continues into central ND, and the
Bismarck/Mandan area is right on the nose of the high PWATs
lifting into the state and there may be a slight west to east
inverted trough along the I-94 corridor. This was enough to
provide a focus point for convection and convection continues
to redevelop along this boundary. Fortunately for the Bismarck
Mandan areas, the convection remains north of the Metropolitan
area. We still have a couple Flood Advisories in effect. The
first for the Bismarck Mandan area and although the rain has
stopped, it will still take some time for the excess runoff to
abate. The second Advisory is for portions of Burleigh and
Morton Counties, north of Bismarck and Mandan. The ongoing
convection remains mostly sub-severe, but with very high
rainfall rates it`s not taking long for localized flooding in
poor drainage areas. Reports of 2-4 inches of rain were pretty
common around the Bismarck Mandan area, with some higher reports
to the north. Most of the rain in the Bismarck Mandan area fell
in around 20-40 minutes.

Mesoscale models are still having a hard time resolving this
evenings convection, so we manually adjusted pops east over the
next few hours. Updated text products will be transmitted
shortly.

&&

.DISCUSSION...
Issued at 237 PM CDT Tue Aug 13 2024

For this afternoon, shortwave energy continues bringing a few
showers and thunderstorms through the forecast area. More recent
CAMs continue to suggest more isolated coverage through this
evening. As the wave moves further eastward, it enters a less
favorable environment where instability decreases and effective
shear is progged to be around 35 kts or less. So while another
strong storm or two isn`t out of the question, the more likely
scenario is isolated showers and with an occasional thunderstorm.

Tonight through Wednesday is the more interesting period. In
concurrence with the prior shift, agree that despite a marginal
risk, severe weather potential looks pretty limited. RAP model
projections suggest 0 to 6 km bulk shear limited at 20 kts or less
for most areas most of the time, and often time 15 kts or less in
areas with the best instability. More importantly for tonight
through Wednesday is the potential for heavy rainfall.

High pressure over the Great Lakes Region will help advect Gulf
Stream moisture into the Dakotas on Wednesday, with mixed layer
dewpoints likely in excess of 60 degrees. More robust shortwave
energy, gradually becoming a more organized low, is projected
to approach the area tonight and pass through the day Wednesday.
Simultaneous surface low pressure will deepen with an elongated
center most likely over Nebraska and/or South Dakota. As this
system lifts to the northeast, weak upper flow will lead to the
potential for training thunderstorms. Should this happen, the
potential for very heavy rainfall and localized flooding exists.

The HREF ensemble mean maintains lower amounts generally at an inch
and a half or less. However, with thunderstorm activity and the
aforementioned potential for training; the HREF max may play out in
localized areas. This would mean an area, most likely in the
south central (including the James River Valley) could see 4 to
5 inches of precipitation where any training occurs. One
potential limiting factor to heavy rainfall is a lack of
instability in the eastern half of the state. This is reflected
in some CAMs which show more shower or thundershower activity
rather than an organized thunderstorm complex.

Beyond Wednesday, northwesterly flow aloft prevails through
Friday with occasional shower and thunderstorm chances. Ridging
looks to be prevalent for the weekend and into early next week
with limited precipitation chances. Overall, expect seasonable
to seasonably cool temperatures during a very gradual warming
trend with highs mostly in the 70s and 80s. With cloudy skies
and widespread rain, Wednesday looks to be the coolest day
overall.

One final miscellaneous note is that elevated smoke will
persist over much of the area through tonight, with lesser areal
coverage Wednesday through Wednesday night. A little
near-surface smoke may also begin to filter into the west
especially during the day Wednesday. Any visibility reductions
from smoke should be limited.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 108 AM CDT Wed Aug 14 2024

Showers and thunderstorms are expected to become widespread across
western and central North Dakota on Monday. Torrential rain will
reduce visibility to IFR levels at times. MVFR to IFR ceilings are
also expected to settle over most of the state early Wednesday
morning, with gradual improvement from west to east in the afternoon
and evening.

&&

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

&&

$$

UPDATE...Hollan
DISCUSSION...Telken
AVIATION...Hollan