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860
FXUS63 KBIS 210322
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1022 PM CDT Fri Sep 20 2024

.KEY MESSAGES...

- Expect low to medium chances (25 to 50 percent) for showers
  and thunderstorms tonight. The best chances will mainly be
  north of the Highway 200 corridor.

- Windy conditions are possible late tonight into the day
  Saturday behind a cold front, with sustained winds ranging
  from 20 to 25 mph.

- A cooling trend is forecast through the weekend and into early
  next week, with forecast highs this weekend in the 60s. Some
  areas of frost are possible Sunday morning across the west.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1014 PM CDT Fri Sep 20 2024

A strong thunderstorm developed in eastern Montana, producing
severe gusts, and now has moved into northwest North Dakota. It
is less organized than an hour ago so we issued a SPS for 55mph
winds. Another thunderstorm in Renville County has formed. This
one could have a hail threat, not sure yet with little CAPE.
This is all being fed by the cold front moving in. The storm
moving into North Dakota has a low level jet at its back. The
marginal risk continues in this area, and we have put
thunderstorms back into the forecast.

UPDATE
Issued at 650 PM CDT Fri Sep 20 2024

A surface trough is producing scattered showers on the leading
edge through central North Dakota. Meanwhile storms on the
Canadian border on the cold front move east/northeast. We did
get in a marginal risk of severe weather this evening in the
far northwest, however the threat is very very low. There is not
much CAPE or shear. Plus, the cold front is almost all the way
through the marginal risk area anyways, and no storms formed.
The rest of tonight will be breezy as the cold front sweeps
through, with scattered showers mainly west and north.
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&&

.DISCUSSION...
Issued at 313 PM CDT Fri Sep 20 2024

Mostly clear skies are present across much of North Dakota this
afternoon, with some high clouds moving into the northwest ahead of
a large upper level trough over southern Saskatchewan, as well as
some fair weather cumulus in the southwest. At the surface, very
weak low pressure sits to our northwest, with a somewhat tightened
pressure gradient fueling some slightly breezy southwesterly winds
in the west. Temperatures mostly remain within the 70s, with some
areas in the southwest potentially seeing highs in the low to mid
80s.

Through the rest of the evening, the aforementioned trough is
forecast to slowly make its way eastward, with an associated cold
front beginning to approach the Dakotas. As a result, cloud coverage
is forecast to increase in the northwest, expanding eastward heading
into the evening. There will be enough synoptic scale ascent to help
aid the formation of showers ahead of the front as well, however
instability remains very limited, with only an isolated thunderstorm
or two expected. Steepening low level lapse rates ahead of the front
has lead to a very small portion of the northwest being included in
a Marginal Risk (level 1 of 5) from the SPC. Some gusty winds are
possible with these storms, but otherwise the threat remains very
marginal given the very low instability and lack of deep layer
shear. Winds are forecast to decrease closer to sunrise,
shifting to more westerly later tonight prior to the arrival of
the front.

Late tonight and early Saturday morning, the aforementioned cold
front is forecast to sweep across the state, moving from northwest
to southeast. Chances for showers will continue to move east across
the state ahead of this front, with a line of showers extending from
the Turtle Mountains to the southwestern corner of the state. A
secondary push of precipitation is possible across the north as
well. These waves of precipitation should exit the area by sunrise,
at which point the winds will begin to increase behind the front.
After veering more northwesterly, sustained wind speeds will
increase to around 20 to 25 mph, with gusts up to 35 mph possible.
One thing to note, right as the front initially moves through, winds
could become quite gusty, with model soundings indicating the mixing
height dropping to around 200 ft and substantial height falls along
the front. Winds could briefly exceed advisory criteria for an hour
or two, but our current thinking is that once the front moves
through, the winds should moderate back to 20-25 mph. Definitely
something we`ll keep an eye on in case winds behind the front begin
to trend higher than anticipated. Otherwise, overnight lows tonight
range from the lower 40s west to lower 50s in the James River Valley.

As the trough moves east, positioned to the north of the
International Border, cooler air will fill into North Dakota,
resulting in a cooling trend through the weekend. High temperatures
on Saturday will sit firmly in the low to mid 60s, with Sunday
seeing highs generally in the mid to upper 60s. Breezy northwesterly
winds will continue through the day on Saturday, beginning to
decrease in the afternoon and evening as the front moves out of the
area to our east. On the back side of the trough, surface high
pressure is expected to strengthen and transit the western half of
the state, resulting in clearing skies Saturday evening and
overnight into Sunday morning. As a result, low temperatures
Saturday night into Sunday morning are forecast to be in the mid 30s
in the west, raising concerns for frost in the area. Areas of
frost will be possible, with the most likely areas being the
usual cold corridors in the southwest as well as portions of the
northwest. Current deterministic guidance is suggesting light
winds, clear skies, and dominant high pressure in the west
during this period, so there is potential for these low
temperatures to decrease a bit further. Once again, this will be
something to monitor closely as we approach the weekend.

Beyond this weekend, a mostly dry pattern is expected through the
rest of next week. Aloft, a secondary trough is forecast to pass
across the Northern Plains on Monday and Tuesday, but the forcing
remains rather week, keeping chances for precipitation very low.
From Tuesday onward, long range guidance suggests ridging building
in from the west, thus beginning another warming trend. High
temperatures will range largely from the mid 70s to mid 80s by
Thursday and Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
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Issued at 1014 PM CDT Fri Sep 20 2024

VFR ceilings and visibilities through the period. Mid level
clouds tonight with scattered rain showers and a possible
thunderstorm. Winds around 20kts from the south, turning
northwest with a cold front overnight. Low level clouds will
briefly move in after 06z in the north. Saturday will continue
to be breezy from the northwest at 30kts.
-- End Changed Discussion --

&&

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

&&

$$

UPDATE...Smith
DISCUSSION...Besson
AVIATION...Smith