246
FXUS63 KBIS 151945
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
245 PM CDT Sun Sep 15 2024

.KEY MESSAGES...

- Warm and dry today with temperatures mainly in the 80s.

- Thunderstorm chances return tonight through Monday night with
  some strong to severe storms possible along with locally
  heavy rain.

- An active pattern continues through the week, with strong to
  severe storms again possible on Tuesday, along with a general
  cooling trend from mid to late week.

&&

.DISCUSSION...
Issued at 245 PM CDT Sun Sep 15 2024

A weak surface cold front is pushing across the northern Plains
this afternoon, promoting a reorganization of the previously
variable winds to become east east southeasterly wind with
sustained speeds from around 10 to 15 mph. The passage of this
cold front, along with the high pressure building in behind it,
has promoted the generally dry conditions found today, along
with high temperatures generally in the 80s this afternoon.

The northern Plains is set to see a fairly active upper level
pattern through the short term as an obstinate upper level low
parked over the eastern CONUS will, in turn, promote the
development of upper level troughing over the western CONUS.
With southwesterly flow thus found over much of the northern
Plains, periodic shortwaves ejecting out of this trough will
promote near daily chances for showers and thunderstorms over
western and central North Dakota through much of the coming
workweek. This first of these chances will develop this evening
as a shortwave and associated surface low center over northern
Wyoming will hijack the previously mentioned weak cold front,
bringing it slowly back north as a warm front. Conditions near
the surface are expected to remain fairly stable though with a
low level jet draped across the south central, increasing
moisture behind the front promoting increased instability - with
models MUCAPE values progged from 1500 to 2000 J/KG - and at
least sufficient shear could allow a few stronger and maybe a
marginally severe storm to organize across the southwest and
south central late this evening and overnight into Monday
morning. The hazards associated with any severe thunderstorms
that do develop this evening and overnight would mainly be winds
up to 60 mph and some large up hail up to quarters in size. In
their most recent update, SPC has included portions of
southwestern and much of central North Dakota into a Marginal
(level 1 of 5) risk for severe thunderstorms for today.

Ongoing showers and thunderstorms trailing behind the warm
front are expected to persist and move across central North
Dakota overnight through Monday, along with persistant moisture
transport driving dewpoint temperatures into the upper 60s and
lower 70s across this after by Monday afternoon. With
instability maximized by this period, with model MUCAPE values
falling into the 1500-2500 J/KG range, the potential for severe
thunderstorm is somewhat higher on Monday than it today. The fly
in the ointment is again the available shear across the
forecast are during this period that, while still sufficient for
severe thunderstorm development, is stymied by poor mid level
flow. As such, the main hazards associated with any severe
storms that do develop across central North Dakota on Monday
would be hail to the size of quarters and winds up to 60 mph.
There also is some potential for an isolated tornado, with a
decent veering wind profile and low LCLs across the James River
Valley. Current, the SPC has placed much of central North Dakota
into a Marginal (level 1 of 5) risk for severe thunderstorms on
Monday. With redeveloping convection along the slow moving warm
front and PWATs exceeding 1.5, some areas could see locally
heavy rainfall. Otherwise on Monday, south southeasterly winds
will strengthen behind the warm front, with sustained speeds
from 15 to 20 mph and gusts from 25 to 30 mph generally
expected, with the highest speeds across the south central,
south of the I94 corridor. Seasonable warm temperatures, with
highs generally in the 80s, also continue on Monday, though
portions of the north central ahead of the warm front will only
reach the mid to upper 70s.

Monday night into Tuesday morning, the upper level trough will
close off as it tracks over the Rockies, promoting a transient
upper level ridge that will help clear out any lingering showers
and thunderstorm over the forecast area during the early
morning hours. Late Tuesday afternoon and Tuesday evening,
another cold front will be dragged through the northern Plains
as the previously mentioned surface low begins to move northward
into Canada. Another round of showers and thunderstorms are
anticipated to develop along and behind this front Tuesday
evening, with some potential for severe weather shifting in out
of eastern Montana and over the western Dakotas. As it stands,
the SPC has placed much of western and portions of south central
North Dakota into a Marginal (level 1 of 5) risk for severe
thunderstorms on Tuesday. High temperatures will also peak ahead
of the cold front on Tuesday, forecast from around 80 in the
north central to the lower 90s in the southwest.

As the the inciting upper level low begins to shift northward
into the Canadian Prairies Wednesday, the another upper level
low will dig into the western CONUS and sustain the active
weather pattern through at least the end of the workweek. The
potential for, the timing of, and the strength of any showers
and thunderstorms become increasingly uncertain this far out,
however, especially as the better moisture returns from the golf
experienced earlier in the week is expected to be cut off in
the later half. There is better agreement for a cooling trend
through the end of and into next week, as NBM forecast highs
drop broadly into the 60s by the coming weekend and into next
week. Individual ensemble members remain fairly discordant to
the degree of cooling however, with a 5 to 10 Fahrenheit spread
between clusters depending on the relative speed and strength of
the second low passing through the northern Plains by the end
of the forecast period.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 1245 PM CDT Sun Sep 15 2024

Mainly VFR ceilings and visibility are anticipated at all TAF
sites throughout the 18Z TAF period. Overnight into Tuesday,
showers and thunderstorms are expected to develop over portions
of southwestern and central North Dakota, with convection being
possible over the terminals KBIS and then KMOT during this
period. As such, we have included VCTS and -SHRA at those
terminals for this update. Chances for showers will also be
found at KDIK and KJMS, though confidence is lower at this time.
As such, VCSH have been added to those terminals. Where showers
or thunderstorms do develop, MVFR ceilings and variable winds
are possible. Otherwise, variable winds will organize behind a
weak cold front moving through western and central North Dakota
today, becoming south southeasterly this afternoon with speeds
from 10 to 15 mph, before generally diminishing overnight
through the end of the TAF period.

&&

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

&&

$$

DISCUSSION...Adam
AVIATION...Adam