805
FXUS63 KBIS 020030
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
730 PM CDT Sat Jun 1 2024

.KEY MESSAGES...

- Scattered severe thunderstorms will be possible Sunday
  afternoon and evening. Threats include large hail up to the
  size of golf balls, damaging winds up to 60 mph, and a tornado
  or two possible.

- Chances for showers and thunderstorms begin late tonight and
  continue through the first half of next week. Temperatures
  will be near to slightly above average, with highs in the
  lower 70s to lower 80s through much of the work week.

- Strong west to northwest winds are possible Tuesday through
  Thursday.

&&

.UPDATE...
Issued at 725 PM CDT Sat Jun 1 2024

For early evening update, main change was adjusting low
thunderstorm chances for overnight. A look at latest RAP
soundings shows a modest but still relevant low level jet
developing over the James River Valley into parts of central
North Dakota late tonight through the overnight hours.
Therefore, have broadened out the low chances for thunderstorms
a bit. Also increased cloud cover over most locations on Sunday
afternoon given the expected convection.


&&

.DISCUSSION...
Issued at 318 PM CDT Sat Jun 1 2024

This afternoon, a weak surface high pressure was centered over
south central North Dakota, underneath cyclonic flow aloft from
a strong closed low over the northern Canadian Prairies. Skies
across the forecast area were mostly sunny, aside from some fair
weather cu across our northern tier of counties. A westerly
breeze continued up north as well from a marginal surface
pressure gradient, with highs this afternoon in the 70s across
the area.

Just upstream over Montana, an embedded shortwave in quasi-zonal
flow aloft was moving east, with an associated expansive cirrus
field. A surface low is expected to deepen in southern Montana
attendant to this wave, and move east into the Dakotas on
Sunday. Ahead of this surface low, a warm front will lift north
late tonight Sunday morning, likely triggering convection
across north central North Dakota through the morning. The
surface low and attendant cold front are also expected to cross
into western North Dakota sometime in the early morning hours as
well, bringing additional precipitation. At this point, we
aren`t expecting any severe weather in the morning either in
north central or in western North Dakota, with southeast return
flow still increasing and bringing in additional instability.

Midlevel height falls will move into central North Dakota in
the early afternoon, which is when the potential severe thunderstorm
window opens. There is still a moderate amount of uncertainty
regarding the evolution of the severe threat considering the
timing and placement of the two different fronts, as well as if
earlier convection doesn`t progress as expected. The 12Z HREF
paints max UH tracks both in north central North Dakota earlier
in the afternoon, where there is less confidence in any storms
becoming severe, and then in the south central and James River
Valley in the late afternoon and early evening, where confidence
is a bit higher. Forecast MLCAPE values range from ~1000 J/kg
in the north to up to 2000 J/kg across the south, with bulk
shear from 30 to 40 knots and modest low- and mid- level lapse
rates. Of note, guidance is advertising storm relative helicity
values up to 200 m2/s2 in the southern James River Valley, which
aids in tornado potential.

Recent CAMs agree the most on convection spreading south and
east through the afternoon, overcoming a weak cap that is
forecast across the south central/east. The general expectation
is for convection to become cluster/linear as it moves through
the James River Valley and then into eastern North Dakota, which
makes sense based on storm relative flow being more parallel
than perpendicular to the front, although this will depend on
the timing of the front. If we were to have any cells stay
discrete in the James River Valley tomorrow afternoon and
evening (potentially ahead of the front), these would have the
highest threat ceiling given the forecast environment, so
something to keep an eye on. If we do end up with a primarily
linear storm mode, it would favor mostly a wind threat, although
we could not rule out a quick spin up tornado along the leading
edge of convection.

We do still have a Slight Risk (Level 2 out of 5) that was expanded
slightly to the west with the midday update from SPC. Potential
hazards continue to be hail up to the size of golf balls, damaging
wind gusts up to 60 mph, and a tornado or two. Latest estimated
timing has severe storm potential from 12 PM to 8 PM CDT. With
the expected progressiveness to this system, it is likely that
storms will be east of the forecast area by the late evening.

A shallow ridge builds in on Monday for a quick warmup and the
warmest day of the period, with forecast highs in the mid 70s to
lower 80s. The break from precipitation will be short-lived as
another quick-moving wave moves west to east, with showers and
thunderstorms likely Monday evening, through the night, and
through much of Tuesday before tapering off. The timing of the
front does not seem favorable in guidance for much severe
potential, although a low-level jet kicking in late Monday could
keep convection strong into the morning hours. The latest CSU
machine learning probabilities are now showing a low potential
for severe weather on Monday.

We then transition to a very broadly northwest flow pattern,
with near-normal temperatures most of the work week. The ECMWF
EFI is signaling the potential for strong winds across the area
Tuesday through Thursday, with the highest likelihood on
Wednesday. Late in the week, there is increasing confidence in
a stout upper ridge building in over the western half of the
CONUS. The eastern extent of the ridge will influence how warm
temperatures get, but for now there is moderate confidence in
widespread highs in the 70s to end the work week, with
temperatures warmer in western North Dakota and cooler in the
east. Precipitation chances drop off substantially under this
pattern, although this will also be influenced by the location
of the ridge axis, and if any embedded shortwaves move through.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 725 PM CDT Sat Jun 1 2024

VFR conditions through this evening. Late tonight into the
overnight hours, isolated thunderstorms will be possible over
central and eastern North Dakota as a low level jet develops.
Numerous showers and thunderstorms will develop over western
North Dakota Sunday morning, spreading east. Some storms may
become severe Sunday afternoon, mainly over central and eastern
North Dakota.

&&

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

&&

$$

UPDATE...JJS
DISCUSSION...Jones
AVIATION...JJS