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389
FXUS63 KBIS 180550
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1250 AM CDT Tue Jun 18 2024

.KEY MESSAGES...

- Widespread showers with isolated to scattered thunderstorms
  through Tuesday.

- Isolated to scattered severe storms possible this evening
  through tonight, with expected hazards of hail up to golf ball
  size and winds up to 60 mph. Very heavy rainfall is also
  possible with any storm, possibly resulting in localized
  flooding.

- Below normal temperatures expected Tuesday and Tuesday night,
  followed by temperatures trending warmer and another active
  period developing for later this week.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1231 AM CDT Tue Jun 18 2024

Severe thunderstorm watch continues for the far south central
into the James River Valley through 6 AM. Strong convection
continues along the ND/SD border from Emmons into Logan and
McIntosh counties. This looks to be our main concern over the
next few hours with MUCAPE above 3000 J/KG and over 50 knots of
effective shear. 0-3KM shear is also around 50 knots. The
limiting factor is the elevated nature of the convection. Will
continue to monitor.

UPDATE
Issued at 1045 PM CDT Mon Jun 17 2024

Quick update to issue Severe Thunderstorm Watch 431 for most of
south central North Dakota and the James River Valley.

UPDATE
Issued at 1006 PM CDT Mon Jun 17 2024

Showers and thunderstorms continue to increase in coverage and
intensity across much of western and central North Dakota. The
most intense storms are currently located from just north of
Bismarck to McLean and Sheridan counties, riding along the
MUCAPE gradient. This line has a history of producing 60 to 70
mph winds so it will have to be watched closely as it skirts the
BisMan metro area and beyond. Storms should continue to
intensify over the next couple of hours as the low level jet
increases. More strong to severe storms are likely in the short
term.

UPDATE
Issued at 637 PM CDT Mon Jun 17 2024

Thus far, the forecast is panning out as expected as an arc of
showers and thunderstorms has developed extending from the
southwest part of the state and into the north central. The
buoyancy environment here is not very impressive, with MUCAPE
values only maxing out generally in the 500 to 1000 J/kg range.
MLCAPE is pretty much non existent at this point. That being
said, very high effective and deep layer shear is in place and a
better instability environment should advect into the south
central and southeast through the night. Thus, we are still
expecting some strong to severe storms to develop somewhere in
the 10 PM to midnight time frame across the southwest or south
central and sweep quickly out of the James River Valley by the
2 AM to 4 AM time frame. Thinking remains the same with regards
to the most likely hazards: hail up to the size of golf balls
and 60 mph winds. Heavy rains training over the same areas could
also lead to some localized flooding.
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&&

.DISCUSSION...
Issued at 215 PM CDT Mon Jun 17 2024

Currently, strong southwest flow aloft with a 90-100kt upper
level jet aloft. Mid level low/S/WV trough moving into the
Montana Rockies, with multiple lead embedded waves moving across
the Dakotas today, resulting in scattered showers and extensive
cloudiness. Still only seeing trace amounts of moisture reported
across the north underneath showers there, so don`t see the need
to increase POPs much for the next few hours.

Looking at two rounds of showers/storms over the next 12-18
hours, the first will be convection firing up to our southwest
as increasing ascent develops east into the high plains
(currently clear and becoming unstable), with this activity
then quickly moving/developing to the northeast into western ND
this evening. The overall severe threat will be limited with
minimal instability projected, though with 60-80 knots of 0-6km
shear, a few organized updrafts can`t be ruled out, hence the
Marginal Outlook being maintained. Northwest ND looks to see the
heavier rainfall amounts, upwards to an inch and half. Given
the limited strength expected and fast progression of storms,
these amounts will likely fall over a few hours vs. several
minutes, so do not anticipate any hydro issues northwest.

Second round of convection looks to originate across South
Dakota (possibly far southern ND) mid to late evening, as the
aforementioned forcing continues east and interacts with
increasing MUCAPE developing from south to north across SD and
into parts of south central and southeastern ND. 0-6km shear not
as robust, but still in the 40-50 kt range so can`t rule out a
few large hail producers. It does appear that the threat for
heavy rain and localized flooding is becoming an elevated
concern, with PWATs nearing max climatology values of 1.5". Thus
will continue to mention this in our messaging (HWO and social
media).

Much cooler air is pulled south across the Northern Plains in
the above S/WV`s wake, with highs Tuesday ranging from the 50s
northwest to around 70 in the far southeast. Overnight lows
Tuesday night/Wed morning continue to be a closely looked at,
with NBM continuing its cooling trend with now widespread
mid/upper 30s across the west. For now, will not mention frost
but will def need to keep an eye on this period over the next
24-36 hours.

We never really get out of the active west/southwest flow
pattern, but precipitation chances looks more isolated through
Thursday, until we trend more active later this week as models
bring in more defined waves into our local region. Temperatures
will also trend slightly warmer Wed-Fri, then more-so later this
weekend into early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
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Issued at 1231 AM CDT Tue Jun 18 2024

Ceilings will continue to drop tonight as showers and
thunderstorms track east across easter portions of the forecast
area. Widespread LIFR to MVFR stratus will be possible at times
pretty much through Tuesday morning. A few strong to severe
storms may also be possible over the James River Valley,
including KJMS. The strongest storms will have the potential to
produce golf ball size hail and winds to 60 mph. If one of the
stronger storms move overhead, brief IFR visibilities will be
possible along with gusty and erratic winds. The strongest
storms should move out of the area by around 3 AM or so.
-- End Changed Discussion --

&&

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

&&

$$

UPDATE...TWH
DISCUSSION...TWH
AVIATION...TWH