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451
FXUS63 KBIS 170319
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1019 PM CDT Sun Jun 16 2024

.KEY MESSAGES...

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- Widespread showers with isolated to scattered thunderstorms
  Monday through Tuesday.

- Isolated to scattered severe storms possible late Monday
  afternoon through Monday night, 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.

- Below normal temperatures expected this week, especially
  Tuesday and Tuesday night.
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&&

.UPDATE...
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Issued at 1013 PM CDT Sun Jun 16 2024

Showers are slow to develop to our south, with limited radar
returns entering our area. We`ve lowered PoPs across the south
as a result. CAMs really are not very supportive of much
precipitation across the south at all until around 10z, so we`ve
also slightly reduced PoPs until that point as well. Otherwise,
the forecast remains on track. Winds have died down across the
area for the most part, and will continue to do so heading into
the overnight hours.

.UPDATE...
Issued at 702 PM CDT Sun Jun 16 2024

The winds across the northern portions of the state have
continued to decline steadily through the late afternoon, and
are expected to continue decreasing through the evening. Most
sustained wind reports we are seeing are already below
criteria, with only a few isolated reports right around 30 mph.
Thus, we allowed the Wind Advisory to expire at 700 PM CDT.
Otherwise, some high clouds continue to stream in from the
southwest, while some cumulus continues to move into the area
from the southern Canadian prairies. Some little showers may
move into the northern portions of the state this evening, but
they are quite isolated in nature. As such, the forecast remains
mostly on track.
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&&

.DISCUSSION...
Issued at 256 PM CDT Sun Jun 16 2024

A closed upper low at the base of a negatively-tilted trough is
spinning northeast across the Canadian prairie provinces this
afternoon, with a deeper trough further upstream over the Pacific
Northwest. This places the Northern Plains under southwest flow
aloft. The attendant surface low is located just slightly
northeast of the upper low, placing the Northern Plains in the
dry and relatively cool sector. The associated strong pressure
gradient has maintained sustained winds around 30 to 35 mph and
gusts to around 50 mph in northwest and far north central parts
of the state. A Wind Advisory remains in effect for much of
western and north central North Dakota until 7 PM CDT, but
southern portions of the advisory are not expected to be as
windy as it is to the north.

The southwest flow aloft will become more energized tonight as the
Pacific Northwest low begins to kick into the Northern Rockies. Most
guidance projects widespread convection developing along and north
of a thermal/buoyancy gradient draped across South Dakota and
southern Minnesota. The northern fringes of this activity may push
into the James River Valley late tonight into Monday morning, but
even the most aggressive guidance with the northward extent of the
MUCAPE gradient now keeps it just south of the ND/SD stateline. We
have therefore ceased messaging an isolated severe threat for this
forecast time period. There could still be a few rumbles of thunder
in the southern James River Valley late tonight into Monday morning,
and small hail is a reasonable worst case scenario.

Increasing cloud cover, and to a lesser extent chances for rain, are
in the forecast for Monday morning and afternoon. Confidence in the
timing of PoPs in this part of the forecast is not particularly high
given the broad but weak synoptic scale ascent. There are low
chances for thunderstorms during the day Monday, but SBCAPE is
nonexistent and MUCAPE will be slower to increase. From late Monday
afternoon through Monday night and into Tuesday morning, showers
should become much more prevalent across the entire state as a 700
mb trough approaches from the west while strong low to mid
level moisture transport arrives from the south. Thunderstorm
probabilities over this time period increase from northwest to
southeast, with projected MUCAPE ranging from near zero in the
northwest corner of the state to possibly as high as 3000 J/kg
in the James River Valley. A quick examination of deterministic
model soundings from Ashley to Jamestown shows there could be
little to no convective inhibition atop the surface inversion
layer (which could be nearly completely saturated with
mist/drizzle/fog at the surface), so there is at least some
potential for more robust convection. While shear at all layers
originating from the surface is quite high, the values
significantly drop off when taking into account that the storm
inflow layer is forecast to be 1-2 km AGL, which could render
effective bulk shear lower than 30 kts. Because the difference
between a 1.5 km AGL and 2 km AGL storm inflow level could
result in a substantial difference in effective bulk shear,
which is within the realm of possible outcomes, we will continue
to message golf ball size hail as the main expected hazard from
the strongest convection. We did however lower our wind gust
forecast to 60 mph, owing to the stability of a deeper, nearly
saturated boundary layer with negligible DCAPE forecast at this
time. Another hazard that bears monitoring with this system is
the potential for very heavy rainfall considering a very deep
warm cloud layer (LCL-FZL) and anomalously high PWAT.

Showers remain in the forecast on Tuesday as the trough shifts into
the Northern Plains, which should push the instability required for
deep moist convection off to the east. An unseasonably cold air mass
will also filter into the region, which combined with cloud cover
could keep afternoon highs lower than 60 in western parts of the
state. There seems to be a favored solution for surface high
pressure developing near or a little north of the Black Hills
Tuesday night. Should this occur under a mostly clear sky, southwest
parts of the state could see overnight temperatures colder than 40,
which is already being advertised by deterministic NBM output. A
somewhat active southwest flow pattern is favored to persist from
mid to late week, with a modest warm up back to mostly 70s for
highs. The highest chances for showers and thunderstorms per NBM
guidance are from late Thursday through late Friday, higher south
than north.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 702 PM CDT Sun Jun 16 2024

VFR conditions are present across all terminals, and will remain
VFR through the TAF period. Gusty westerly winds continue to
decrease through the evening, becoming light and variable across
the entire area overnight. Gusty northeasterly winds and broken
cloud decks around 5kft return near the end of the TAF period,
roughly around 20z, as low pressure and associated pressure
gradient push into North Dakota from the south. Chances for rain
increase within the last 3 hours of the TAF period as well,
though confidence is rather low when it comes to exact location
of rain.

&&

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

&&

$$

UPDATE...Besson
DISCUSSION...Hollan
AVIATION...Besson