923
FXUS63 KBIS 201520
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1020 AM CDT Wed Aug 20 2025

.KEY MESSAGES...

- Hot, humid, and breezy weather today, with moderate to high
  heat impacts. Most of western and portions central North
  Dakota is in a Heat Advisory this afternoon.

- Isolated severe thunderstorms are possible this evening and
  overnight, mainly west and north.

- Isolated severe thunderstorms possible in the east Thursday.

- Much cooler temperatures, lower humidity, and mainly dry
  weather is expected Friday through Tuesday.

&&

.UPDATE...
Issued at 1020 AM CDT Wed Aug 20 2025

Main update was to assess the current Heat Advisory. Blended
high temperatures to be closer to the NBM 50th for today, which
did raise them slightly. This combined with dewpoints in the
upper 60s to lower 70s could bring Heat Index values around 100
for most of western and portions of central ND. Heat Risk also
raised to major for a lot of these areas given these conditions.
Given the potential for widespread heat impacts, and heat index
values near to over 100, decided to expand the Heat Advisory to
include all of western and portions of central North Dakota.
Confidence in the southwest is still modest given forecast
lowering dewpoints today, although decided to include this area
for the time being as air temperatures could still be around 100
degrees. Otherwise, some elevated convection continues to
linger in the north. Added some slight PoPs through the morning
to account for this.

UPDATE
Issued at 625 AM CDT Wed Aug 20 2025

The backside of the ridge (positive vorticity) has been creating
scattered showers in western North Dakota, as the ridge axis is
now in central North Dakota. They have seemed to mostly all
die off now. Clusters of thunderstorms in southern Canada may
cross the border into far north central and northeast North
Dakota for the next few hours. Any patchy fog should start to
burn off now that the diurnal heating has started.

&&

.DISCUSSION...
Issued at 327 AM CDT Wed Aug 20 2025

Currently the ridge axis aloft has moved into western North
Dakota. With this, a strong thermal ridge is associated with it
at 850mb. At the surface, a low pressure sits in central
Montana, with a cold front.

Today will be very warm and breezy, with that low pressure
creating a pressure gradient across the state. With the cyclonic
flow around the low, winds will be out of the south at around
30 mph. High temperatures will be the warmest in the west,
where the thermal ridge and highest wind gusts will be located.
Today will also be another day of high humidity with dew points
in the upper 60s and lower 70s.

Isolated strong to severe storms are possible this evening and
overnight when the cold front slides into North Dakota around
00z. The warm and humid afternoon will create 1500-3000 J/kg of
MUCAPE across central North Dakota. Shear ahead of the front is
only 20 kts, but with the front it is up to 50 kts. SPC has the
northwest and north central in a marginal level 1 risk for this
evening and overnight. One major limiting factor will be cap
that this strong thermal ridge creates at 850mb. The thermal
ridge is much weaker in the north central, so that will be the
highest chance for a severe storm. The rest of the state, when
the cold front moves in, could see just general storms. The cold
front is mainly just at the surface, hence why the thermal
ridge is going to affect this event so much. (surface based
storms will run into the capping layer) The isolated severe
storms are possible all night and into Thursday morning for
central and eastern North Dakota. SPC has another marginal for
the eastern half of the state Thursday, but this is mainly for
lingering storms after 12z. By Thursday afternoon the cold front
will be in South Dakota and Minnesota, and so will the storm
chances.

Thursday is the start of our cooldown as northwest
flow become dominate. Highs will range from the upper 70s
northwest to mid 80s south. Friday through early next week,
highs only warm to the 70s. During this time, humidity will be
much less as well. Looking at dew points only in the 40s and
50s, compared to the 60s and 70s that we`ve been experiencing.
With the northwest flow, little to no storms are forecast.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 625 AM CDT Wed Aug 20 2025

VFR through the period, except in the south central this
morning. Scattered IFR CIGs are present until 14z. Winds will
gust around 25kts from the south today. Slight chance of storms
in the evening in the north central. Overnight chances for
storms increase in the north and central.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT /6 PM MDT/ this evening for
NDZ001>003-009>011-017>021-031>034-040>045.

&&

$$

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