829
FXUS63 KBIS 160325
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1025 PM CDT Wed May 15 2024

.KEY MESSAGES...

- Daily chances for precipitation continue through the week into
  early next week.

- A low potential for a strong or severe storm Friday
  afternoon/evening.

- Warming trend through Friday, then a modest cooldown for
  Saturday.

&&

.UPDATE...
Issued at 1025 PM CDT Wed May 15 2024

At 10 PM CDT, a line of showers was entering northwest North Dakota
from the west. These showers are being maintained by a low-
amplitude, eastward-propagating mid level shortwave preceding a more
pronounced wave on water vapor imagery that was moving into
southwest Saskatchewan. Lightning activity with these showers has
decreased over time, and with MUCAPE diminishing to zero just east
of the MT/ND border, will maintain a forecast with no thunder
mentioned. Isolated to scattered shower activity will remain
possible across western and spreading into central North Dakota
overnight, with a decrease in coverage expected Thursday morning.

Confidence is increasing in two separate areas of thunderstorm
potential Thursday afternoon and evening. One is over south central
North Dakota in the late afternoon and the other is in the northwest
later in the evening. In both areas, CAPE is only forecast to be
marginal at best, likely less than 1000 J/kg. While effective bulk
shear will remain weak in south central North Dakota, an approaching
upper jet will increase shear over time in the northwest, possibly
reaching 40 kts concurrent with the highest chances of storms.
Surface based convection could initiate along a thermal gradient
across southern Saskatchewan Thursday afternoon, with mid level
forcing assistance from falling heights. Shortwave energy could then
bring this convection southeastward into northwest North Dakota, but
it would likely transition to an elevated inflow layer by the time
it moves into the state. Nevertheless, a stronger storm or two with
hail and stronger wind gusts are a reasonable outcome for northwest
North Dakota Thursday evening. CAMs with earlier forecast
initialization times were more robust in simulating a couple of
longer, notable UH tracks, but 00Z CAMs have come in more
subdued.

UPDATE
Issued at 715 PM CDT Wed May 15 2024

Scattered showers are being maintained over the James River Valley
early this evening by an inverted surface trough underlying the base
of a mid level trough. This activity should diminish closer to
sunset.

Extensive cloud cover wrapping around the surface low over far west
central Minnesota continues to slowly erode from west to east over
central North Dakota this evening. Due to the clearing skies with
light winds and residual boundary layer moisture, we anticipate some
patchy fog developing later tonight into Thursday morning, mainly
across areas including Linton, Bismarck, Steele, Harvey, Rugby, and
Rolla.

Isolated to scattered showers preceding a shortwave ejecting off the
Canadian Rockies are ongoing across northeast Montana. At 7 PM CDT,
a couple of isolated showers were approaching the state border,
while a more persistent line of showers with occasional lightning
was tracking east through Glasgow. The PoP forecast has been updated
to account for observed trends.

&&

.DISCUSSION...
Issued at 134 PM CDT Wed May 15 2024

Current surface analysis places low/trough over the eastern
Dakotas, with frontal boundary dropping southward through the
plains. Upper level analysis places trough stretching from the
Northern Plains south/southwestward towards the central/southern
Rockies. Over our area, some light rain showers continue to
gradually dissipate over the James River Valley, while lingering
low cloud cover over much of the area has started to diminish
in earnest over western areas.

For the rest of this afternoon into tonight, clouds will
continue to gradually diminish from west to east, with showers
ending as the aforementioned upper trough over the area pushes
east. West-northwest flow sets up over our area but a modest
short wave will make its way through the flow and start its
approach late tonight, bringing low rain chances (~20 percent)
to northwest parts of the area. The wave will continue its way
across northern parts of the area Thursday morning, with
continued modest chances.

As we go through late Thursday into Thursday night, a trough
drops into the Pacific Northwest with flow shifting
southwesterly over our area and becoming active. This will bring
the start of an extended period of shower/thunderstorm chances.
At this time Friday looks to bring the greatest chances,
especially overnight over central and southwest North Dakota
(60-80 percent). There is a hint at some strong to severe
thunderstorm potential as models are hinting at elevated
instability (possibly 500-1000 J/kg) with ample deep layer shear
for rotating updrafts. The fly in the ointment may be the
timing of the forcing, as that seems to be overall lagging a
bit as of this moment. With that said, the potential for the
timing to eventually overlap a bit is there, and is being
picked up by the CSU machine learning severe guidance which is
showing a potential over central and parts of southwest North
Dakota, so will continue to monitor. Friday also looks to be the
warmest day, with highs pushing into the mid 70s to mid 80s.

Cooler air moves in for Saturday, with a modest rebound for the
upcoming week. Pattern remains active, with daily chances (20-40
percent) for precipitation.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 1025 PM CDT Wed May 15 2024

MVFR/IFR ceilings and visibility are becoming more prevalent at
KJMS than was expected. Recent satellite trends have shown a
slowing of the erosion of low clouds from the west, and it is
possible that the low ceilings could translate into a persistent
fog/mist through the night. Elsewhere, VFR conditions are likely
through the forecast period, with a few possible exceptions.
Patchy fog could develop later tonight into Thursday morning
across central North Dakota. There are also low to medium
chances for showers expanding across the state from west to east
through the night, which could bring a brief period of MVFR
visibility. The major terminal most likely to be impacted by
rain overnight is KXWA. Additional shower and thunderstorm
development will be possible Thursday afternoon, with the
highest chances at KBIS. Light winds are expected through
tonight, becoming westerly around 10 kts on Thursday.

&&

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

&&

$$

UPDATE...Hollan
DISCUSSION...JJS
AVIATION...Hollan