157
FXUS63 KBIS 181739
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1239 PM CDT Mon Aug 18 2025

.KEY MESSAGES...

- Isolated thunderstorms are possible today. A few may be
  strong to severe across the south central, with the main
  hazards being hail the size of ping pong balls and wind gusts
  to 60 mph.

- Warmer and drier weather expected through mid week. Some
  moderate heat impacts are possible Wednesday.

&&

.UPDATE...
Issued at 1231 PM CDT Mon Aug 18 2025

Showers have all but diminished across the south. We are still
seeing a few radar echoes but little, if any, precipitation is
making it`s way to the ground. Did hold onto low precipitation
chances (20 percent) here for another couple of hours just in
case there are a few pockets of light rain. Otherwise, no major
changes were needed for the early afternoon update. Just blended
in the latest observations to the going forecast.

UPDATE
Issued at 853 AM CDT Mon Aug 18 2025

The Dense Fog Advisory will be allowed to expire on time at 9 AM
CDT. While visibilities have improved markedly, we are still
seeing a bit of patchy fog across portions of the James River
Valley and the greater Devils Lake Basin. Patchy fog may linger
in these areas for another hour or so along with stratus before
eroding from west to east.

Showers and weak thunderstorms across the southwest and south
central continue to diminish but at least some lightning will
remain possible near the South Dakota border as they move east
and weaken.

UPDATE
Issued at 645 AM CDT Mon Aug 18 2025

Showers and thunderstorms continue to slowly move east through the
southwest and now into the south central. A few storms could
produce gusts up to 40mph. These storms should slowly die as the
morning goes on, or so the CAMs forecast. The storms have been
persistant all morning, so we shall see. Otherwise the dense fog
continues in the north and east. The outflow boundaries from
the storms are starting to clear out the fog from west to east.

&&

.DISCUSSION...
Issued at 442 AM CDT Mon Aug 18 2025

Currently a disturbance in the southwest flow, and a surface
front, is popping non-severe thunderstorms in southwestern North
Dakota. Small hail is possible with these, but the environment
does not support severe strength. These should continue their
eastern propagation. The CAMs have these storms dying soon,
however there are no signs of this. Especially as they are
riding the front and could form more off the outflow. The
expectation is they travel to the south central later this
morning and die as a few CAMS have forecast. The other weather
event ongoing is dense fog. Along, north, and east of the
Missouri River dense fog has been ongoing all night. An Advisory
for the fog is in effect until 9am CT. We will likely be
cancelling the western counties early, as the storms mentioned
above get closer. On radar the outflow boundary is visible 50
miles ahead of the storm clusters, and is clearing out the
ground clutter on radar. As the outflow moves east, it will push
the fog or dissipate it earlier than 9am. It also looks like the
outflow is weakening as the very moist air mixes into it.

The rest of today will be warm with highs in the 80s, and dew
points in the 60s. Therefor we are in a marginal risk in the
south central for severe storms. The timing looks to be in the
late afternoon through the evening. Most CAMs have development
around 21z. Models have around 1500 J/kg of MUCAPE, and only
20kts of shear. So storms are very possible, but the question
will be if that is enough shear to create lasting storms that
produce severe hail. We are going with a forecast of ping pong
size hail and 60mph winds as forecasted yesterday. It is
something to note that not every CAM has storms at all, and the
NBM only has a small area of slight PoPs.

The rest of the week a broad ridging pattern will takeover,
with a very strong thermal ridge mid-week. Tuesday and Wednesday
could have near dangerous heat indices in the west with highs
nearing 100 degrees. Wednesday night a cold front will sweep
through the state, creating slight (20%) chances for storms
overnight and through the day Thursday in the southeast. Flow
aloft will switch to the northwest through the weekend. This
will give us a break from the high heat and humidity through the
weekend with highs in the 70s and lows in the 40s. By Sunday,
however, another ridge forms in the western CONUS and creates
another thermal ridge over us. Highs will climb back into the
80s for next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1231 PM CDT Mon Aug 18 2025

For the most part, quiet weather is expected through the 18z TAF
period. There is a chance for some fog overnight tonight across
the north central, Devils Lake Basin, and James River Valley,
potentially leading to some MVFR visibilities at KMOT and KJMS.
Otherwise, VFR conditions are expected through the period with
generally light winds.

&&

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

&&

$$

UPDATE...ZH
DISCUSSION...Smith
AVIATION...ZH