216
FXUS63 KBIS 181010
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
510 AM CDT Sat Jul 18 2026

.KEY MESSAGES...

- Seasonably warm temperatures in the mid 80s to lower 90s
  today, then hot conditions return on Sunday with high
  temperatures and heat index values around 95 to 100.

- Scattered severe thunderstorms are possible Sunday afternoon
  and evening. Expected hazards include hail as large as 2
  inches in diameter and damaging winds up to 70 mph, with a
  tornado possible.

- Critical fire weather conditions are possible across parts of
  southwest and south central North Dakota on Monday.

- Cooler, but still near to slightly above normal temperatures
  are favored through most of next week.

&&

.DISCUSSION...
Issued at 510 AM CDT Sat Jul 18 2026

Upper level ridge has re-amplified upstream, with its axis from
along the Alberta/Saskatchewan border through eastern Montana
and Wyoming early this morning. A surface high pressure is
centered over North Dakota, which has allowed temperatures to
fall into the 50s for the first time in several days and patchy
fog to develop despite increasing high clouds. The fog has
reduced visibility to a quarter mile in some spots at times, but
believe this to be shallow fog and very dissimilar to the dense
fog outbreak from 24 hours ago. The fog should be short-lived
this morning, giving way to a mix of clouds and sun with
seasonably warm high temperatures in the mid 80s to lower 90s.
Weak shortwave energy rounding through the top of the ridge
could bring some sprinkles or light rain showers to parts of the
area throughout the day, but model soundings show clouds bases
well above 10,000 ft, and there is also little to no CAPE
forecast through this evening.

Weak disturbances may continue rounding through the top of the
ridge tonight into Sunday morning, and a warm front is expected
to enter western North Dakota by early Sunday morning. This
could lead to more widely scattered showers and perhaps a few
thunderstorms as the warm air advection drives MUCAPE to around
500-1000 J/kg. CAMs favor any showers or storms diminishing over
central North Dakota by late Sunday morning as the magnitude of
warm air advection decreases, but not all CAMs simulate
convection to begin with. The early day passage of the warm
front will allow hot and humid conditions to return to most of
western and central North Dakota Sunday afternoon. Forecast
highs in the southwest quadrant of the state, including
Bismarck, are around 100 degrees, with lower 90s in the far
northwest and Turtle Mountains area, and mid to upper 90s
elsewhere. Higher forecast dewpoints in the 60s on Sunday lend
to a maximum heat index forecast that is near or greater than
the high temperature forecast for most locations. This places
much of southwest and central North Dakota at risk for heat
indices around 100, with the highest confidence in exceeding 100
over south central North Dakota. The forecast maximum wet-bulb
globe temperature risk is also solidly in the Extreme category
over south central North Dakota, and patches of Extreme reach as
far north as the Highway 200 corridor.

Confidence is increasing in an isolated to scattered severe
thunderstorm threat Sunday afternoon and evening. A potent
shortwave is forecast to dig into central Saskatchewan Sunday
afternoon, forcing mid level height falls over the Northern High
Plains. A cold front with very weak baroclinicity attendant to
the surface cyclone near the Saskatchewan shortwave is forecast
to enter western North Dakota early Sunday afternoon and
gradually drift eastward, reaching northeast to south central
North Dakota by late evening. Most CAMs are simulating enough
forcing, diurnal BL heating, and/or cooling aloft to overcome
MLCIN and initiate deep moist convection at some point mid to
late afternoon. Initial storms appear favored to develop
somewhere from northwest to north central North Dakota, with
additional development farther south in the late afternoon to
early evening. Weak to moderate forcing in an antecedently
capped environment with shear and deep layer wind vectors all
perpendicular to the surface cold front strongly favors a
discrete mode, although CAMs do want to trend toward more of a
mixed/cluster mode by early evening, likely owing to the
potential for strong cold-pool establishment and propagation
within a deep and well-mixed boundary layer. Forecast CAPE
along and ahead of the cold front approaches 3000 J/kg, with
0-6 km shear around 40 to 50 kts and increasing over time. All
these environmental parameters would support supercells with
very large hail up to 2 inches in diameter and damaging RFD
winds up to 70 mph. Upscale growth into linear complexes or
bowing segments seems unlikely at this time, but if this were to
occur, the most likely maximum wind gust forecast would need to
be revisited. Finally, despite high LCLs and weak low level
shear, there is a conditional risk for a tornado with a very
similar setup to what was observed last Thursday. Forecast CAPE
and shear would both be sufficient for tornadogenesis with any
supercell that remains anchored to the vorticity-rich and
baroclinically-weak surface boundary.

The Saskatchewan shortwave is forecast to dive into the
northern Red River Valley and head toward the western Great
Lakes on Monday, bringing a stronger and more baroclinic cold
front through the region. Precipitation chances are very low
with this cold front, and there is little to no buoyancy
forecast to be available. The timing of the cold front moving
from north to south during the daytime hours is likely to limit
highs to around 80 to 85 across the north. But in southern North
Dakota, the timing is such that compressional heating could
give a local boost to high temperatures, which are still
forecast to reach around 90 to near 95. Windy conditions are
expected on Monday with the cold air advection, tightening of
the surface pressure gradient, and mean BL layer winds around
25-30 kts. Strong diurnal mixing could lower dewpoints into the
40s across parts of southwest and south central North Dakota
Monday afternoon, yielding RH around 20 to 25 percent. With
northwest winds sustained around 25 mph and fuels reported to be
rapidly drying from southwest North Dakota to around Lake Oahe,
critical fire weather conditions could develop Monday
afternoon.

Tuesday is still favored to be the coolest day next week with
highs in the mid 70s to mid 80s as surface high pressure extends
from Alberta to North Dakota. The cooldown may be shorter lived
than previously anticipated though as ensembles now favor a
quicker departure of the downstream trough over the Great Lakes,
allowing the upstream ridge to shift east off of the Rockies by
next weekend. The NBM now returns lower to mid 90s for highs
south and west of the Missouri River Wednesday through Friday,
with mostly 80s to the north and east. And looking further
ahead, there is a distinct shift of the temperature
distributions in the warmer direction next weekend, with the
rate of increase of the 75th percentile outpacing that of the
25th percentile (increasing spread, but the 75th percentile
already exceeds 100 degrees at Bismarck, for example).
Precipitation chances remain quite low next week, but the
northwest flow could become more active in latter parts of the
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 510 AM CDT Sat Jul 18 2026

Patchy fog is possible across central North Dakota this morning,
with visibility reductions as low as a quarter mile at times.
The fog should lift by mid morning, and VFR conditions are
otherwise anticipated through the forecast period. Expect
predominantly south to southeast winds across the western half
of the state, with speeds during the day today ranging from
near 15 kts at KXWA and KDIK to only around 5 kts at KJMS.

&&

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

&&

$$

DISCUSSION...Hollan
AVIATION...Hollan