645
FXUS63 KBIS 160858
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
358 AM CDT Mon Sep 16 2024

.KEY MESSAGES...

- Thunderstorm chances return through tonight with a isolated to
  scattered severe thunderstorms possible, along with very
  heavy rain.

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

&&

.DISCUSSION...
Issued at 208 AM CDT Mon Sep 16 2024

Convection is developing over Mercer, Oliver and McLean counties
of central North Dakota. This is near/ahead of an east to west
band of 35-40kts of effective shear and on a gradient of strong
MUCape (2000J/KG) to the south and weak (<500J/KG) to the north.
This is also on the nose of a quite strong low level jet
lifting north-northwest through central/western ND. This
activity has the ingredients to produce severe hail up to ping
pong ball size and possibly some locally gusty winds. The main
question here is will everything line up, and for how long.
Shear and instability is quite low just to the north, but
everything is also propagating quickly north. Also wondering if
the ingredients from the EMC RAP are keeping up with the rapid
development and northward propagation of severe ingredients.
Nonetheless we could see scattered strong to severe storms
continue over central ND for a few hours yet early this morning.

For today, ongoing convection over central ND will continue to
drift to the north and east through the day. Severe ingredients
will remain and SPC has introduced a slight chance for severe
storms over south central into northeast North Dakota, with a
marginal risk extending back southwest into far southwest ND.
Besides the potential for severe storms we will also need to
monitor for the potential for very heavy rain and areas of
localized flooding, especially if we would see multiple round of
storms or training of storms. The MCV mentioned from the central
High Plains convection looks like it`s lifting north northeast,
a bit farther to the west than was noted yesterday, which is
likely the reason the marginal risk was pulled back more into
southwest ND. This area will remain quite unstable today,
actually pretty much everywhere south of the warm front that
lifts north through the forecast areas, and multiple impulses
will continue to lift northward through the upper level flow.
However the greatest risk will likely exist within the slight
risk area from the south central into northeast ND. Will also
mention a possible tornado over the slight risk area. This area
will be favored for strong low level helicity this afternoon
with low lcl`s. Will mention golf ball sized hail and 60 mph
winds across the the slight and marginal risk area, which covers
all but the far northwest CWA.

Tonight into Tuesday morning, the western 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 upper low an its associated surface low lifts
north 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. 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, with a Slight (level 2 of 5) risk for severe storms
over northeast Montana and skirting portions of far northwest
ND. 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 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, the better moisture returns from the golf looks to be
cut off late in the week. There remains better agreement for a
cooling trend through the end of the week, as NBM forecast
highs drop broadly into the 60s by the coming weekend. Low
temperatures also drop with overnight lows mainly in the 40s
but with 25th percentiles dropping into the mid and upper 30s
over western ND late in the weekend and into early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1220 AM CDT Mon Sep 16 2024

Chances for showers and thunderstorms will increase across central
North Dakota overnight and persist through much of the day
while slowly drifting eastward. MVFR/IFR visibility will be
possible with any storm, but hail and strong wind gusts are much
less likely in the overnight hours. Outside of thunderstorms,
VFR conditions are likely to prevail, though some lower ceilings
cannot be ruled out in and around areas of showers and storms.
Easterly winds around 5 to 10 kts through the night will turn
to the southeast and increase to 10 to 15 kts on Monday, with
some higher gusts possible in the afternoon, before diminishing
by early evening.

&&

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

&&

$$

DISCUSSION...TWH
AVIATION...TWH