242
FXUS63 KBIS 211954
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
254 PM CDT Fri Jun 21 2024

.KEY MESSAGES...

- Showers are likely this evening, with a chance for
  thunderstorms (20 to 30%). Chances for precipitation decrease
  to mostly 15 to 30% overnight.

- Chance of showers and thunderstorms (ranging from 20% south
  to 70% north) return Saturday. A few afternoon or evening
  storms over central North Dakota could be strong to severe,
  with the main expected hazards being quarter sized hail and 60
  mph winds.

- Temperatures increase through the weekend, topping out in the
  80s north to lower 90s south on Monday, then slightly cool to
  the upper 70s to upper 80s through next week.

- Mostly on and off chances for precipitation (ranging from 20
  to 40%) last through next week, with the best chances for
  showers and thunderstorms on Monday and Thursday.

&&

.DISCUSSION...
Issued at 248 PM CDT Fri Jun 21 2024

Some pop-up showers that originated in far eastern Montana have
moved into western and central North Dakota, congealing into a large
area of showers covering much of south central North Dakota. Some
rumbles of thunder are possible with this area of showers, but its
not expected to intensify much more than it already has. Some
additional pop-up showers and isolated thunderstorms have formed
across the north as well, moving into Canada and bringing about some
short-lived locally heavy downpours of rain. Given the lack of
instability and forcing across our area, severe development is not
anticipated through the rest of the evening and into tonight. Weak
surface high pressure is analyzed over northeastern North Dakota,
while an inverted surface trough sits to our southwest across
Wyoming. Aloft, southwesterly flow persists around the southern edge
of a trough, helping bring about the weak forcing needed for the
current showers. Temperatures across the south were kept pretty cool
due to the overcast decks that built in through the morning, with
highs only reaching into the mid 60s in some areas. These showery,
cloudy conditions are expected to continue into the overnight hours,
though the chances for precipitation decrease to around 25 to 50
percent through this period. Lows tonight remain largely in the 50s.

Saturday sees the arrival of a quick moving shortwave aloft,
swinging through the southern edge of the aforementioned trough and
helping bring about another wave of showers and thunderstorms. With
warmer temperatures filtering in, instability is forecast to
increase through the afternoon and evening hours, mostly across
central North Dakota and the James River Valley. Current
deterministic analysis suggests a large area in that region of 1000
to 2000 J/kg of MUCAPE, while the northern half of that region sees
a narrow corridor of 40 to 50 kt 0-6 km bulk shear. As a result, the
SPC has outlined much of our northern areas with a Marginal Risk
(level 1 of 5) for severe weather. For the few brief hours that
these ingredients line up, any storm that forms could certainly
strengthen and produce 60 mph wind gusts and quarter sized hail, but
given how marginal the ingredients themselves are, the risk for this
will remain somewhat low. Otherwise, Saturday is expected to bring
in the beginning of a brief warming trend, with highs in the mid 70s
to lower 80s expected.

Sunday and Monday will continue the warming trend as a thermal ridge
builds in from the southwest, helping raise temperatures into the
mid 80s and lower 90s by Monday. Flow aloft on Sunday will shift to
northwesterly as a ridge quickly builds into the area as well,
resulting in a fairly dry and mostly clear day on Sunday. Flow aloft
shifts to become more zonal Sunday night, which leads into a
potentially wetter Monday.

While Monday is expected to be the warmest day in the forecast
period, it is also of particular interest due to the severe
potential across the far eastern portions of our area (most notably
in the James River Valley). Given the heat, as well as the moisture
that has continued to be transported into the area from the south
recently, instability will be plentiful, along with more than enough
shear needed to sustain strong to severe storms. Current
deterministic guidance suggests prominent midlevel height falls,
nearly collocated with an axis of modest ML mixing ratios and MUCAPE
ranging from 2500 to 3500 J/kg, along with roughly 40 kt 0-6 km bulk
shear. The main factor reducing the confidence with this setup is
the forcing needed to get these storms going; whether that be the
location of the most prominent height falls, the location of the
surface warm front, or the location of the attendant surface low
sweeping through the area. The ingredients are absolutely there for
a risk for severe weather, but without knowing where storms will
fire off, we can not say for certain where in our area this threat
will be. Regardless, there is still a chance for sub-severe
thunderstorms and showers in the James River Valley, but confidence
is just too low to expand that chance further west into our area.

From Monday night onward, we are expecting to enter another semi-
active and warm pattern, with mostly zonal flow aloft through the
end of next week. Ridging to our southwest will nudge some continued
warm air into our area, keeping high temperatures firmly in the mid
70s north to mid 80s south. Chances for precipitation are also
pretty spotty, with the middle of the week appearing to be fairly
dry, while the end of the week may see some slight chances of
showers and thunderstorms. However, given how weak the impulses are
that would bring us these chances for rain, confidence is fairly low
in the timing and extent of these showers. Come Friday, there are
some relatively large differences in some of the long range models,
with some solutions indicating another drier and warmer period
beneath a potent ridge, while other solutions suggest continued
zonal flow aloft with daily chances for precipitation. Taking a look
at the most recent WPC cluster analysis, it appears to be around a
60/40 split, favoring the solution that brings about the more
prominent ridge. At the very least, we can expect continued warm
temperatures in the 70s and 80s, potentially reaching into the 90s,
by the end of next week and into next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1233 PM CDT Fri Jun 21 2024

Showers and thunderstorms have developed and are moving through the
northwestern and southwestern portions of the state, with further
development expected into the south central over the next few hours.
As such, every terminal (with the exception of KMOT) is expected to
enter IFR/LIFR conditions within the next 4 hours, with KDIK and
KXWA already seeing IFR/LIFR ceilings and visibilities. Showers and
thunderstorms will continue on through the day today, moving east.
Overnight, IFR ceilings will continue to prevail across nearly the
entire area, while chances for thunderstorms and showers decrease
heading into Saturday morning. Winds will initially be generally
easterly around 10 kts, becoming light and variable overnight,
shifting to the west at around 10 kts by Saturday afternoon.

&&

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

&&

$$

DISCUSSION...Besson
AVIATION...Besson