798
FXUS63 KBIS 181150
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
650 AM CDT Fri Oct 18 2024

.KEY MESSAGES...

- Periods of light rain will continue across south central and
  eastern North Dakota through this afternoon, with expected
  amounts around a few hundredths to one quarter inch.

- Unseasonably warm and dry weather will return for the weekend
  into early next week.

- Near-critical fire weather conditions are expected in
  northwest and west central North Dakota on Saturday.

&&

.UPDATE...
Issued at 649 AM CDT Fri Oct 18 2024

The forecast for today remains on track. Current conditions and
trends were blended in for this update. Periods of light rain
will continue to fall from south central North Dakota to the
James River Valley throughout the day, with a lull expected
around midday.


&&

.DISCUSSION...
Issued at 311 AM CDT Fri Oct 18 2024

Early morning upper air analysis places a deep trough over the
western CONUS, with amplified ridging from the Great Lakes to the
Gulf Coast. A surface cold front extends from the Manitoba/Ontario
border to the Nebraska panhandle, with upstream high pressure trying
to build over southern Saskatchewan. The upper level pattern places
southwest flow aloft with a continuous stream of cyclonic shear
vorticity over the Northern Plains. This, combined with low to mid
level frontogenesis and the right entrance region of an upper jet,
is providing enough forcing for scattered rain showers from western
South Dakota through central North Dakota early this morning. As the
day progresses, a closed upper low is forecast to cutoff from the
base of the western CONUS trough while the northern stream flow
remains progressive. This will pivot the axis of scattered showers
slightly in a clockwise direction so that the rain will mainly be
located over south central and eastern North Dakota later this
morning through the afternoon, followed by a dissipation and
eastward drifting of the rain this evening. Forecast rainfall
amounts of a few hundredths to near a quarter of an inch remain on
track, but there will likely be a sharp drop-off in additional
accumulations to zero to the north and west of the axis of rainfall.
A mostly cloudy sky will keep afternoon temperatures in the 50s
today, closer to 50 where periods of light rain persist and closer
to 55 to 60 where it remains dry.

A southwest-northeast oriented surface ridge axis is forecast to
slide through the region tonight. Its timing should promote strong
radiational cooling, especially in the favored corridor from the
southwest corner of the state to just south of Lake Sakakawea. The
low temperature forecast for tonight was decreased as low as the
50th percentile of the NBM distribution, giving lower to mid 20s in
the aforementioned corridor and upper 20s to mid 30s elsewhere.

Mid to upper level flow will turn more zonal on Saturday as the
southwest cutoff low continues to detach itself from the northern
stream. Low level to surface flow will become southwesterly and
strengthen as the pressure gradient force is tightened between
deepening low pressure over Alberta and the departing surface ridge.
This will make for a breezy day on Saturday for most areas, but
windy will be a more appropriate term for the northwest where
sustained speeds near 25 mph and gusts to 35 mph are likely. Given
the favorable low level wind orientation for strong diurnal mixing,
the high temperature forecast on Saturday was bumped into the 50th
to 75th percentile range of the NBM distribution, resulting in 60s
across all of western and central North Dakota. Humidity could fall
as low as 25 percent across much of western North Dakota Saturday
afternoon, which combined with the southwest winds is expected to
result in near-critical fire weather conditions.

The zonal flow pattern looks to continue into early next week, with
a possible low amplitude ridge over the area as the southwest cutoff
low drifts into the Central Plains. Ensemble guidance shows high
confidence in well above normal temperatures Sunday through Monday,
with very low spread in the NBM. Highs are mainly expected to be in
the lower to mid 70s both of these days, and nighttime temperatures
before, in between, and after these two days are likely to remain
above freezing. For late Monday through Tuesday, the cutoff low is
forecast to open as it nears the Great Lakes while a shortwave
ejects from the base of a Pacific Northwest trough and quickly moves
east along the international border. These two features are the
cause for low to medium precipitation chances (20 to 40 percent) in
the most recent NBM Monday evening through Tuesday night. Cluster
analysis does not reveal any stark contrasts in potential outcomes,
and all solutions display only low QPF at most (the NBM probability
of at least 0.25" is less than 10 percent). Temperatures should
return closer to normal on Tuesday and be notably cooler north
compared to the south. The cold front attendant to the shortwave is
also likely to create breezy conditions on Tuesday.

Beyond Tuesday, ensembles tend to favor another period of dry
weather with above average temperatures for mid to late next week,
with mean upper ridging over the western/central CONUS. Although, it
should be noted that average temperatures are rapidly falling this
time of year.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 649 AM CDT Fri Oct 18 2024

Periods of light rain will continue across south central and
eastern North Dakota this morning and afternoon. Ceilings and
visibility should mostly remain VFR. Previously thought KJMS
would see a period of MVFR ceilings, but confidence in this has
lowered. Therefore, included a TEMPO group for this set of TAFs.
Winds will generally be out of the north around 10 kts today,
with some higher gusts across south central and southeast North
Dakota.

&&

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

&&

$$

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