651
FXUS63 KBIS 291955
AFDBIS

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

.KEY MESSAGES...

- Seasonably cool temperatures today, with highs in the 60s.

- 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.

&&

.DISCUSSION...
Issued at 255 PM CDT Sat Jun 29 2024

A seasonably cool late June day continues today, as a broad
high pressure is centered over North Dakota and has been
filtering in cooler air through the day. Widespread cloud cover
associated with an exiting surface low and attendant upper
shortwave has been quite slow to exit, and still extends across
much of southwest and south central North Dakota. North of this
stratus, fair weather cumulus has developed, which will diminish
later this evening with the loss of (rather limited) daytime
heating. Highs will be in the 60s across the area. Cool and
quiet tonight, with lows in the mid 40s to lower 50s.

Sunday is forecast to be warmer and more active, as a shallow
ridge quickly builds over the Northern Rockies before flattening
as an embedded wave moves through later on Sunday. Southerly
return flow will boost highs back into the lower 70s to lower
80s, with dew points around 60 degrees in southwest North
Dakota. With the approaching wave, a surface low is progged to
deepen over northern Wyoming and move east/northeast. The
tightening surface gradient should produce breezy southeast
winds across the entire forecast area, and strong winds across
the southwest, closer to the center of the low. There is some
uncertainty on if winds will be advisory-level but will likely
be close.

High-res guidance is relatively consistent on scattered
convection developing off the higher terrain in Montana late in
the afternoon and through the evening, moving east towards North
Dakota. The main concern is that with a stronger thermal ridge
in place across western North Dakota, capping will be too
strong for convection to overcome. However, a low- level jet in
place could potentially be enough for strong to severe
convection to sustain itself as it crosses the state line into
an environment characterized by up to 1000 J/kg of bouyancy and
35-45 knots of bulk shear. The 12Z HREF has a few max UH tracks
crossing into western North Dakota late Sunday evening around
midnight, but the more likely threat is west of the forecast
area. SPC continues a Day 2 Slight Risk (level 2 of 5) focused
on parts of western North Dakota, with a decreasing risk to the
east. Our threat message remains consistent, with expected
hazards being hail up to the size of quarters and wind gusts up
to 60 mph.

To start the work week, a deepening upper trough and closed low
will continue pushing east into the central CONUS on top of a
relatively moist airmass. CSU machine learning and SPC are both
highlighting parts of the central and eastern Dakotas for severe
thunderstorm potential ahead of the trough base and attendant
front that are expected to move through Monday afternoon and
evening. The expectation is that this potential will likely be
dependent on what happens Sunday night into Monday morning, and
if that lessens the higher threat ceiling for convection on
Monday. For now, deterministic guidance is advertising a narrow
plume of instability around 1500 J/kg, and with seasonably
strong bulk shear around 50 knots, it would be a sufficient
environment for strong to severe storms to develop.

The work week looks relatively consistent, temperature wise,
with highs generally from the mid 70s to mid 80s. Persistent
cyclonic flow aloft is expected to continue the active pattern
we`ve been in, with on and off chances of showers and
thunderstorms through the work week. Currently, the highest
blended POPs are during the day on the Fourth of July, so will
have to watch how precip chances trend through the next couple
of days.

NBM 25th/75th percentile spreads are showing modest confidence
in the coolest temperatures late this week before a warming
trend through the weekend. This is from general consensus in
ensemble guidance for a broad upper ridge to develop across the
western CONUS late next week. However, it is worth noting that
there is a small cluster of ensemble members, around 15 percent,
that has the ridge axis much further to the east. NBM
percentile temperature spreads aren`t too large for this amount
of lead time, generally around 10 degrees, but a shift of tails
on the cooler side does indicate a fair amount of ensemble
members advertising highs cooler than the 25th percentile. The
question then becomes whether temperatures are near normal, in
the lower 80s, or above normal, in the mid to upper 80s. NBM
precipitation probabilities are noticeably lower this weekend
into next week than they have been recently, so there are some
signs of a drier period setting up.

&&

.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.

&&

$$

DISCUSSION...Jones
AVIATION...Jones