146
FXUS63 KBIS 181146
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
646 AM CDT Mon Aug 18 2025

.KEY MESSAGES...

- Isolated non-severe thunderstorms across the southwest and
  south central this morning. These could produce gusts up to
  40mph.

- Dense fog advisory for portions of the northwest, north central,
and south central North Dakota, including the James River Valley
until 9am.

- 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 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 /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 645 AM CDT Mon Aug 18 2025

VFR in the west to LIFR north and east in fog. Showers and
thunderstorms are also present in the southwest and south
central, they should slowly move east and die. Did a PROB30 for
KBIS in case they make it that far but confidence is low. These
storms could produce 30kt winds. The LIFR fog should clear out
by 14z. Another round of storms is possible in the central and
east this afternoon and evening, however with low confidence we
left it out of the forecast for now. Winds will stay light
through the period.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CDT this morning for NDZ002>005-
010>013-021>023-025-035>037-046>048-050-051.

&&

$$

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