358
FXUS63 KBIS 211128
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
628 AM CDT Sat Sep 21 2024

.KEY MESSAGES...

- Low chances (20 to 30 percent) of rain showers will continue
  through the early morning hours, mainly across the north
  central and northeast.

- Northwest winds will continue to increase through the morning
  and into the afternoon. Sustained winds to 25 mph and gusts to
  40 mph will be possible.

- Expect cooler temperatures through the weekend and into early
  next week, with forecast highs today and Sunday mainly in the
  60s. Some frost is possible Sunday morning across portions of
  the west.

&&

.UPDATE...
Issued at 619 AM CDT Sat Sep 21 2024

Rain showers continue to diminish and move out. We will continue
to see a few hanging around for another hour or two in the
Turtle Mountains and vicinity and also portions of the James
River Valley. Otherwise, expect decreasing clouds and increasing
winds through the first part of the day. No major change were
needed for this update other than to tweak precipitation chances
based on the latest radar observations and trends.

&&

.DISCUSSION...
Issued at 300 AM CDT Sat Sep 21 2024

An upper level trough and surface cold front continue to move
east across the region early this morning. Forcing from these
two features will maintain low to medium chances (20 to 60
percent) for showers across much of western and central North
Dakota, with the best chances along and north of the Highway 2
corridor. A few rumbles of thunder will also remain possible
along the International border across the north central. While
instability is limited, SPC mesoanalysis does suggest some
pockets of 250 J/kg MUCAPE, likely driven by steep midlevel
lapse rates.

After the trough moves through early today, high pressure will
start to move in later this afternoon and tonight. Showers
should pretty much move out of the area to the northeast by 15z
or so. Clouds will also start to erode from west to east through
the day as high pressure moves in. Behind the front, northwest
winds will also be on the increase through the morning and into
the early afternoon. Most guidance has strong pressure rises and
strong cold air advection sweeping across the state through the
mid to late morning. Very steep low level lapse rates are then
forecast to develop across all of western and central North
Dakota by the afternoon hours. This will mean increasing
northwest winds through the morning and maintaining them into
the afternoon. Sustained values up to 25 mph and gusts to 40 mph
will be possible. As of now, it appears that the strongest
winds will generally be south and east in the mid morning
through mid afternoon. It will be much cooler today with highs
in the lower 60s north to the mid to upper 60s south. Combined
with the windy conditions, it should feel quite blustery, but
there should be plenty of sunshine.

Winds will relax by this evening as high pressure continues to
slide in. A clear sky and generally light winds will lead to a
fairly cold Saturday night/Sunday morning, especially across
portions of the west. The latest NBM shows widespread lows in
the mid to upper 30s across the western third of the state. This
will be a tricky forecast as even the NBM 50th percentile
suggests we will see several more sites in the mid 30s and some
in the lower 30s. If we trend more towards the NBM 25th
percentile, we could see widespread lows in the lower 30s (maybe
even a few upper 20s). As the NBM has warmed slightly over the
last few runs, some uncertainty remains about how low we will go
Sunday morning across the usual cold spots over the southwest.
Pattern recognition would say that we should trend towards the
lower side of guidance but we will continue to roll with
straight NBM for now given the uncertainty. Frost headlines will
likely be needed across the southwest and possibly the entire
west should we, in fact, do trend colder. There was some
discussion of issuing a Frost Advisory on this shift, but we
decided to hold off until the next shift in coordination with
our neighboring offices.

Highs will mainly be in the 60s again on Sunday but it will be a
touch warmer (maybe a few lower 70s returning to the southwest).
Winds will be much lighter was well, so it will likely feel
warmer than it actually is when compared to Saturday. Northwest
flow aloft will dampen through the day on Sunday, becoming
nearly zonal before the next shortwave trough approaches on
Monday. For now, it appears that most of the synoptic forcing
with this next wave will remain north of the International
border. That being said, it wouldn`t be a surprise if we
eventually see some lower rain shower chances introduced late
Monday afternoon or evening.

Ridging starts to move in again by mid to late week, leading to
at least a modest warmup. Highs on Monday are forecast to range
from the mid to upper 60 north to the low to mid 70s south and
then maybe just a touch warmer on Tuesday. By Wednesday through
Friday, the NBM has some low to mid 80s returning to the
forecast as ridging moves across the state and we transition
back into southwest flow aloft.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 619 AM CDT Sat Sep 21 2024

Most of the rain has moved out of the area but we will continue
to see a few showers hanging around the northeast and southeast
for the next hour or two. Some MVFR ceilings have also
developed in the vicinity of KDIK and these should start to lift
over the next few hours. Otherwise, VFR conditions should
prevail through the period. Winds will continue to increase
through the morning and into the afternoon, out of the northwest
up to 25 mph with gusts to 40 mph. The strongest winds will
generally be across the south and east. Winds will start to
relax late this afternoon and into this evening.

&&

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

&&

$$

UPDATE...ZH
DISCUSSION...ZH
AVIATION...ZH