375
FXUS63 KBIS 291747
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1247 PM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Clouds will gradually clear through the day today, with highs
  in the 60s across the area.

- There is a Slight Risk (level 2 of 5) for severe thunderstorms
  across parts of the west Sunday night after sunset. The main
  hazards are hail up to quarter size, and wind gusts up to 60
  mph.

- Breezy winds are expected Sunday, with the strongest winds in
  the southwest.

- There is also a Slight Risk (level 2 of 5) for severe
  thunderstorms across south central North Dakota on Monday.

&&

.UPDATE...
Issued at 1247 PM CDT Sat Jun 29 2024

Widespread fair weather cu have developed behind the main
expanse of stratus with cloud bases around 4 to 6k feet. Early
afternoon temps are still quite chilly for late June, in the mid
50s to lower 60s. We made a few sky cover tweaks, otherwise no
changes needed with this update.

UPDATE Issued at 937 AM CDT Sat Jun 29 2024

The center of a surface high pressure is analyzed over southern
Saskatchewan, northeast Montana, and into northwest Montana,
with a modestly tight pressure gradient still in place over the
James River Valley that is producing breezy northwest winds this
morning. Satellite imagery shows clouds are slowly dissipating
as this surface high and associated drier air moves in, although
this dissipation is progressing a bit slower than expected.
Adjusted sky cover forecast based on satellite trends, otherwise
going forecast looks good.

UPDATE
Issued at 647 AM CDT Sat Jun 29 2024

No significant changes were needed with this update. Low clouds
remain well-entrenched across much of the area, especially over
southwestern ND where there`s a subtle upslope component to the
wind field. However, satellite imagery reveals clearing starting
near the Canadian border and guidance continues to support this
spreading southward through the area by midday. All we did with
this update was blend observed trends into the existing forecast.

&&

.DISCUSSION...
Issued at 358 AM CDT Sat Jun 29 2024

Surface low pressure to our east has helped maintain a deck of low
clouds across essentially our entire area this morning, slowly
moving southeast as the surface low and upper level trough move off
to the east. Some areas of light rain and drizzle are occasionally
being reported, especially below the lowest cloud decks, along with
some areas of patchy fog. As such, we`ve continued the low chances
for precipitation and patchy fog across much of the area, mostly
centered across the central portions of the state, dissipating
through the early morning hours. On the back side of this surface
low, some areas in the James River Valley may see some continued
gusty winds through the morning, decreasing through the daytime
hours as the low pushes east, and as surface high pressure begins
sliding into the area from the west.

Through the day today, we can expect to see a gradual clearing of
clouds from north to south, and a gradual calming of winds from west
to east. As the aforementioned trough moves east into the Great
Lakes region, a ridge positioned over the Rockies will move east
into the Northern Plains, along with a surface high, bringing about
these generally calmer and clearer conditions. Though with the
continued northwesterly flow aloft throughout the day, temperatures
aren`t expected to warm up much at all, with forecast highs largely
in the 60s today.

Sunday appears to be a bit more active, as the upper level ridge is
not expected to persist across our area for long. By mid-day Sunday,
the axis of the ridge will be positioned across the area, along with
the 850mb thermal ridge beginning to nudge into the west. The
surface high pressure will have moved out of our area, with a
deepening surface low across Wyoming beginning to build against the
high to our east. As a result, we can expect to see warmer
temperatures and breezy conditions across the entire area, with the
highest winds expected in the southwest where the surface pressure
gradient is expected to be the highest. The ECMWF EFI currently has
highlighted that area with a value of around 0.8, which helps
further increase confidence in the windy conditions there,
potentially warranting a Wind Advisory in that area.

Heading into Sunday night, we may see our next round of strong to
severe storms, mostly across the west. The SPC has maintained a
Slight Risk (level 2 of 5) for portions of western North Dakota,
while the rest of western and portions of central North Dakota is
outlined in a Marginal Risk (level 1 of 5) for severe weather. Ahead
of the deepening surface low, moisture will be advected into the
northern High Plains, with some parts of western North Dakota seeing
dew points approaching 60 degrees. However, given the strength of
the cap across the west as indicated by model soundings, convection
will be limited during the afternoon and evening hours, despite the
presence of somewhat low instability (roughly around 1000 J/kg of
MLCAPE). The main threat with the convection Sunday night will come
much later, after sunset, as confidence has increased in the 850 mb
nocturnal low level jet (LLJ) strengthening quite a bit in the early
overnight period. With the ongoing convection expected across
eastern Montana moving into the area from the west, this LLJ could
help maintain these storms as they move through, carrying the threat
for large hail and damaging winds. Storm mode remains a bit
uncertain given how conditional this threat is, but if some of these
storms can congeal into an MCS, significant wind gusts could become
the main concern, especially along the nose of the LLJ. With the
environment quickly becoming less supportive of severe storm
development with eastward extent, storms should begin to weaken
relatively quickly as they move east. All in all, the main takeaway
is that this threat will be heavily dependent on the formation of
storms to the west of our area, the true strength of the nocturnal
LLJ, and the overcoming of the cap. If storms do get going, they
could definitely become severe, but the main concern will be if they
can get going in the first place. Given the uncertainty, our current
thoughts for the hazards are wind gusts up to 60 mph, and hail up to
1 inch in diameter.

After Sunday, we can expect to see a continuation of the active
pattern, with near daily chances for showers and thunderstorms
through the work week. Flow aloft will mostly be zonal, with
embedded shortwaves passing through the area each day. On Monday,
the previously mentioned trough and associated surface low are
expected to continue strengthening and moving east across the
central Plains, helping funnel even more moisture north towards the
area. The SPC has outlined portions of our south central in a Slight
Risk for Monday, as well as a Marginal Risk for much of the rest of
our area, as a cold front associated with this surface low sweeps
across the region. While still a bit far out, deterministic guidance
does suggest ample instability and deep layer shear, which would
support the development of a few strong to severe storms. We`ll need
to continue keeping an eye on how this situation develops. One of
the main limiting factors, at least for our area, will be the
effects of the earlier convection on the atmosphere. As a result,
this set up is once again rather conditional, depending quite a bit
on how the convection Sunday night goes. Regardless, temperatures
will remain right around normal for this time of year, with highs
generally in the 70s and lower 80s. Long range guidance tentatively
suggests ridging, drying, and warming for next weekend, with an
increase in temperatures. However, NBM spreads are still rather
large this far out.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1247 PM CDT Sat Jun 29 2024

Low VFR to MVFR stratus deck is in place over southwest and
south central North Dakota to start the TAF period. Although it
is dissipating slower than expected, we are still expecting
terminals to be at VFR conditions within an hour or two of 18Z,
although cloud cover will still be relatively widespread.
Additional fair weather cumulus has developed behind the main
area of stratus, with ceilings around 4 to 6k feet. Northwest
winds will become light overnight, shifting to the southeast
tomorrow and becoming breezy towards the end of the TAF period.

&&

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

&&

$$

UPDATE...Jones
DISCUSSION...Besson
AVIATION...Jones