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733
FXUS63 KBIS 261941
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
241 PM CDT Wed Jun 26 2024

.KEY MESSAGES...

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- Numerous severe thunderstorms (risk level 3 out of 5) are
  likely across the western third of the state late Thursday
  afternoon into Thursday night. Expected hazards include very
  large hail up to 2 inches in diameter, damaging winds as high
  as 70 mph, with isolated gusts up to 80 mph, and a few
  tornadoes.

- Scattered severe thunderstorms (risk level 1 of 5) are
  possible across central ND, including the James River Valley,
  Thursday night. Expected hazards include large hail up to the
  size of ping pong balls and damaging winds as high as 70 mph.

- Below normal temperatures Friday through Sunday, with highs
  only in the mid 60s to lower 70s on Saturday.

- More widespread showers and thunderstorms are favored to
  return early next week. A few storms may be severe.
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&&

.DISCUSSION...
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Issued at 241 PM CDT Wed Jun 26 2024

Before the severe weather threat Thursday, expect mostly quiet
conditions through tonight as CAMs continue backing off on
precipitation. However, with sufficient lower level moisture
and WAA expected, still wouldn`t be surprised if a few showers
and thunderstorms develop late tonight mainly in the southwest
and south central. These thunderstorms are not expected to be
severe, although with instability increasing towards 1000 J/kg
Thursday morning and with adequate shear, a strong storm or two
is possible Thursday morning. A few additional sub-severe
showers and thunderstorms may develop in the northwest and north
central during the early afternoon before the primary threat.

In the late afternoon and evening on Thursday is when the
primary severe weather threat develops. Deepening surface low
pressure over southeastern and possibly into northeastern
Wyoming, along with high pressure over the Great Lakes Region,
will advect very moist air into the state. With the surface high
progged to be a bit further east than even a couple days ago,
this moist air should advect into most of the state rather than
just the west, which will help maintain instability into the
overnight hours east of Highway 83. Resulting mixed layer
dewpoints are progged to reach the low 60s. This will
contribute to a very buoyant atmosphere. Encroaching shortwave
energy off upper low pressure over southern Alberta, along with
a warm or occluding surface frontal boundary associated with
the aforementioned surface low, will help trigger storms
Thursday afternoon.

CAMs are pretty consistent that initial convection associated
with the severe threat is likely to develop in the eastern half
of Montana during the earlier afternoon. Initially, a few
discrete storms might develop. After which, models highly favor
a cluster or line developing. The supercellular period is the
most favorable period of time where all threats are on the table
with the potential for hail that is two inches or greater in
diameter, winds up to 70 mph, and a few tornadoes. We concur
with SPC that the highest risk for tornadic activity is between
approximately 6 pm CDT/5 pm MDT and 10 pm CDT/9 pm MDT. One of
the big questions in regard to whether western ND sees very
large hail or tornadic activity is where any supercells develop
before becoming a cluster/line. Some CAMs have them developing
in eastern Montana, while others have them developing in western
ND.

As storms quickly move eastward, CAMs suggest they weaken
somewhat rapidly especially once they are east of Highway 83.
That said, storms diminishing as quickly as the CAMs suggest
seems potentially a bit fast. While it`s true that instability
and shear decrease during the nighttime hours, they may remain
sufficient enough for a few severe thunderstorms to continue.
As a result, most locations east of Highway 83 are in a marginal
risk (level 1 of 5) with the primary threats large hail up to
the size of ping pong balls and wind gusts up to 70 mph.

Showers and thunderstorms are likely to persist Friday and into
Friday night, especially in the northern third of the state,
before drying out Saturday. More widespread showers and
thunderstorm may return to the forecast area early next week. A
few of these storms may become severe as well.

In regard to temperatures, expect a cooling trend into Saturday
where highs will be in the 60s for most of the state. A warming
trend is then favored for early next week, although uncertainty
on exactly how warm things become remains high at this time. Of
note, lows Friday night are expected to reach the 40s in the
west and north, while lows Saturday night are expected to reach
the 40s in most of the state.
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&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 111 PM CDT Wed Jun 26 2024

Diurnal cu has developed over all, except the far southwestern
corner of the state. This has resulted in mostly low VFR
ceilings. However, there are also some MVFR ceilings in the
north central and the James River Valley. Ceilings should
gradually lift through the afternoon before diurnal cu
dissipates as the sun sets. Isolated to scattered showers and
thunderstorms may develop later tonight in the southwest and
expand across much of the state by late Thursday morning.
However, confidence in development and placement of these
showers and thunderstorms is low overall. More organized showers
and thunderstorms, some severe, are expected beyond the TAF
period late Thursday afternoon and into Thursday night.

&&

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

&&

$$

DISCUSSION...Telken
AVIATION...Telken