938
FXUS63 KBIS 011811
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
111 PM CDT Mon Jul 1 2024

.KEY MESSAGES...

- There is a Slight Risk (level 2 of 5) for severe thunderstorms
  this afternoon and evening in southern North Dakota, and a
  Marginal Risk (level 1 of 5) for much of the rest of the area.
  The main hazards are hail up to ping pong ball size and wind
  gusts up to 60 mph.

- Breezy conditions are expected in the James River Valley
  today.

- The chance for showers and thunderstorms on Independence Day
  is 70 to 80 percent across all of western and central North
  Dakota.

&&

.UPDATE...
Issued at 110 PM CDT Mon Jul 1 2024

Limited changes needed at this time. Morning convection has
moved off. Much of the area is now capped, although some
elevated storms are starting to move into southwestern ND.
Forecast overall remains the same as we wait to see when and if
the front can erode the cap and bring severe weather. To help
determine strength of the cap we are going to launch a 20z
sounding. This should also help with determining hazards for
this afternoon and evening, which for the time being remain the
same.

UPDATE
Issued at 1014 AM CDT Mon Jul 1 2024

Morning convection is slowly dissipating or moving east,
although a lingering boundary is trying to develop new
convection. Overall the atmosphere has limit instability
currently, as evident by some developing wave/billow clouds.
A cold front is still expected to push through this afternoon
and evening and bring another round of showers and
thunderstorms. Severe weather is still possible with this front.
Of note are some morning CAMS initiating this next round early
to mid afternoon, which may be slightly earlier than previous
forecast. This could indicate the CAMS are overcoming the CAP
earlier or bringing elevated thunderstorms earlier. Overall
today could end up being active with isolated to scattered
thunderstorms, come of which could be severe. For now did not
change much except for some minor changes to PoPs based on the
latest guidance.

UPDATE
Issued at 649 AM CDT Mon Jul 1 2024

The low-level jet has weakened considerably and veered per
recent VAD wind profiler data from KBIS, so the intensity
of convection has gradually diminished compared to earlier.
Recent rapid-refresh guidance captures this trend, so we
used that along with observed trends to make minor changes to
the morning forecast with this update. The rest of the forecast
remains on track, focusing on potential severe storms this
afternoon and evening.

&&

.DISCUSSION...
Issued at 422 AM CDT Mon Jul 1 2024

Showers and thunderstorms continue to roll across the northern half
of our area, while surface low pressure across western South Dakota
continues to move east. Two main areas of convection are present,
with one cluster of storms in Rolette County, and one cluster
heading into McLean County, the latter of which has had quite a bit
of lightning associated with it. While not severe, the frequent
lightning and potential for half inch hail has warranted this
cluster getting some Special Weather Statements as it treks to the
northeast. Additional convection across far eastern Montana is also
making its way into McKenzie and Golden Valley counties, with some
more stratiform rain across the northwestern corner of the state.
All of these areas of showers and thunderstorms should move
northeast/east throughout the night, sustaining themselves with the
presence of a relatively strong low level jet, before exiting into
eastern North Dakota through the morning hours. Winds across the
area have diminished a bit quicker than anticipated, especially
across the James River Valley, though we do expect these winds to
rise within the next few hours to become a bit more gusty than they
are right now.

Monday will see the arrival of another wave of showers and
thunderstorms across the area, this time in the afternoon and
evening hours. Aloft, a trough across Montana is expected to deepen
as it moves east through the day, helping aid the deepening of a
surface low pressure system and attendant cold front. Southerly
surface flow ahead of the cold front will continue to funnel
moisture northward into the Dakotas, helping raise dew points into
the 60s. As a result, we see a rather narrow corridor of instability
positioned north-south across central North Dakota, with
deterministic guidance suggesting MLCAPE values in the 1500 to 2000
J/kg range, alongside 40 to 45 kts of 0-6 km shear. Paired with
modest lapse rates in the area, we have seen consistent CAMs runs
suggesting showers and thunderstorms developing across our area in
the early afternoon, strengthening and moving east and into central
North Dakota in the late afternoon and early evening hours. Storm
mode continues to remain a concern, with model soundings suggesting
the potential for a cluster mode, given the rather straight and long
hodographs along with the deep layer shear being oriented roughly 45
degrees from the main frontal boundary. As such, our thinking for
the hazards remains the same, with ping pong ball sized hail and 60
mph gusts, with a likely timeframe of 3 PM to 9 PM. The SPC
maintains a Slight Risk (level 2 of 5) across the south central, and
a Marginal Risk (level 1 of 5) for a majority of the remaining area.

Chances for precipitation drop off heading into the overnight hours
Monday night, as the surface low pressure system moves northeast
into Canada. The trough aloft will also drift off to the northeast
during this time, helping bring about a gradual clearing through the
overnight hours. This brief dry period won`t last for long, however,
as a more transient shortwave trough embedded within the flow will
pass to our south during the day Tuesday. Some showers and isolated
thunderstorms will make their way through western and central North
Dakota through the day, quickly moving out by the late evening
hours. Severe weather is unlikely given the lack of significant
instability and forcing. High temperatures today and Tuesday will be
mostly in the mid 70s to lower 80s, with overnight lows in the 50s.

The active pattern will continue heading into the second half of the
work week, with chances (30 to 60%) for showers and thunderstorms on
Wednesday. A rather potent trough is expected to begin deepening to
our west Wednesday, bringing about the development of a surface low
pressure system to our southwest and the return of showers and
thunderstorms to essentially the entire area, with the highest
chances in the southwest and south central. The CSU machine learning
guidance suggests a low chance for severe hail, but with marginal
forcing and instability, chances for severe weather remain
relatively low.

As this trough deepens and moves east, this unfortunately will also
lead to continued precipitation chances for Independence Day. NBM
PoPs continue to advertise the greatest chances for precipitation to
be during the day on Independence Day, with essentially the entire
area covered in 70 to 80% chances. Temperatures this day will also
be the lowest of the forecast period, with most areas seeing highs
in the upper 60s and lower 70s. Chances for severe weather are still
a bit fuzzy this far out, but tentatively, guidance suggests very
low chances for any strong to severe storms. All in all, it seems
like Independence Day will be cloudy and rainy, with a chance for
some thunder here and there.

Following Independence Day, we may see a reprieve from the daily
chances for precipitation, as long range guidance is continuing to
suggest a very potent ridge across the western CONUS building east
into the Plains through the weekend and into next week. While we may
see some rain on Friday with an upper level trough passing to our
northwest, the weekend seems to be a bit drier and a bit warmer as
this ridge slowly builds into the area from the west. Details on
Saturday are still a bit up in the air, as some models are picking
up on an additional shortwave tracking to our northeast and bringing
another brief wave of rain to the area, while others are keeping
this feature and its associated rainfall away from us. Regardless,
NBM spreads in high temperatures don`t seem too wide after the
warmup through the weekend, so we are likely to see temperatures
rebound back into the mid 70s to lower 80s after the brief cool
period on Independence Day.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 110 PM CDT Mon Jul 1 2024

Chances for showers and thunderstorms will increase this
afternoon and linger through this evening. MVFR to perhaps brief
IFR conditions will be possible with these storms. Some MVFR
ceilings may also be possible this afternoon ahead of these
storms. Strong winds and large hail will also be possible with
any stronger storm. Thunderstorms then push eastward tonight,
with VFR conditions generally returning. There could however be
some lingering MVFR ceilings through the night and into Tuesday
morning. An isolated shower or thunderstorms is also possible
tonight into Tuesday morning across the north, although
confidence is not high enough to include at this time. Breezy
northwest winds are also expected to return on Tuesday.

&&

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

&&

$$

UPDATE...Anglin
DISCUSSION...Anglin
AVIATION...CJS