461
FXUS63 KBIS 290248
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
948 PM CDT Tue May 28 2024

.KEY MESSAGES...

- Severe storms are possible Wednesday later in the afternoon
  and early evening mainly west of Highway 83. Hail up to the
  size of ping pong balls, 70 mph winds, and a tornado or two
  are the primary threats.

- With this storm complex, there is a 90 percent chance or
  greater of a wetting rain (a tenth of an inch or more) for all
  of western through central ND, including the James River
  Valley.

- Breezy to windy conditions are expected Wednesday, especially
  in the southwest and south central portions where winds could
  gust up to 45 MPH.

- Temperatures remaining near to slightly above average through
  the weekend. Shower and thunderstorm chances will also
  continue (mainly 20 to 40 percent), with a minimum Saturday.

&&

.UPDATE...
Issued at 948 PM CDT Tue May 28 2024

Once again only minor changes were made to tonight`s forecast,
with east-southeast flow becoming established as of mid evening
and observed trends supporting lows in the 40s F. We continue
evaluating the Wednesday late afternoon and evening severe storm
risk, but one signal that`s becoming apparent is the potential
may be confined to far western North Dakota, mainly along/west
of the Highway 22 corridor. We expect significant capping aloft
further east owing to marginal low-level moisture return. The
environment in far western ND will also only have effective-
layer shear ranging from 20 to 30 kt, and as a result, we expect
multicellular to only transient supercell structures. There will
also be a trend toward a linear mode Wednesday evening as deep-
layer shear vectors become parallel to the surface front. The
hazard ceiling will be somewhat restrained given these factors.
Moreover, recent guidance suggests less low-level SRH than past
simulations (now limited below 100 m2/s2 in most output). Given
that and marginal deep-layer shear for sustained supercells,
along with a tendency toward linear modes, it appears that any
tornado risk may be even more limited than earlier thought. If
those trends continue in the full suite of 00 UTC guidance, we
may remove the tornado mention from our outlook messaging. Our
messaged hail size (up to ping pong balls) and wind gusts (up to
70 mph) remain supported by the expected environment and mode.

UPDATE
Issued at 629 PM CDT Tue May 28 2024

No significant changes were needed with this update. Diurnally-
driven cumulus will fade as mixing subsides with the approach of
sunset. Surface ridging is located near a Langdon to Carrington
and Ellendale line as of early evening, and will slowly move to
the east overnight, causing winds to become southeasterly in all
areas by about 06 UTC. Afternoon dewpoints are mainly in the 40s
F, supporting the going forecast of lows in the 40s F tonight.

&&

.DISCUSSION...
Issued at 330 PM CDT Tue May 28 2024

Surface high will exit through tonight, while ridge aloft is
found. The result will be mainly clear and dry conditions. An
increased surface gradient will shift winds to the southeast,
and they may become breezy across the west. This increase in
winds should limited the fog threat tonight. Temperatures
tonight will generally be in the 40s. If temperatures can trend
toward the NBM10th percentile, then some patchy frost is
possible in the east. This is not in the forecast, but important
to note as some areas trended this way for this morning.
Something to monitor. Wednesday will see this increased gradient
will be found across much of the CWA through Wednesday. This
could bring breezy to windy conditions across the forecast area.
Pressure falls through the day and lack of upper level support
creates just enough lack of confidence to hold off on a wind
advisory for now. That being the case, there is a strong low
level jet that develops in the southwest and southcentral for
Wednesday. If these winds can mix down, then gusts 45 MPH are
possible as well as sustained winds around 30 mph. High
temperatures from this southerly flow will warm into the 70s for
Wednesday, perhaps some lower 80s.

SPC has maintained a slight risk for severe weather later in the
day Wednesday through Wednesday night. The forecast is overall
very similar to last night. The threat is conditional, and more
so on the timing of everything along with some weak capping
issues. Low lee of the northern rockies still looks to set up
with a cold front pushing through sometime overnight. The moist
gulf southerly flow will increase dewpoints and instability
Wednesday afternoon into the evening. CAPE will be abundant in
over 2000 J/KG in some areas. However, the stronger overall
shear looks to be found on the back end of the front, with 0 to
6 KM shear in the warm sector forecast to be 25 to 35 knots.
These storms could maybe tap into higher amounts of shear at the
0 to 8 KM level though. The strong low level jet could
contribute to stronger 0 to 1 KM and 0 to 3 KM shear. This
could also bring some adequate helicity to the lower levels,
although the higher values of this are in the 0 to 3 KM layer.
This is shown in some hodographs, with veering in the
atmosphere not starting right away and be slightly elevated.
One last thing to note is the 0 to 6 KM shear vector is more
parallel to the expected surface trough and front. This could
make more discrete cells tougher to come by. Given the
uncertainty, there still remains enough of a threat and window
for severe weather Wednesday afternoon through the evening,
diminishing in the overnight hours. Abundant CAPE and enough
shear with some rotating storms possible will maintain the hail
threat to ping pong. A more organized storm or supercell could
produce an isolated golf ball sized hail. Large DCAPE and
increasing 0 to 3 KM shear will maintain wind gust threat up to
70 MPH. There still remains an isolated tornado threat if a more
discrete cell can get going before the front moves through.
Heavy rain is also possible with any storm that develops as Pwat
values are in the 90th percentile and over an inch.

Cold front then takes over showers and thunderstorms sometime
Wednesday night and pushes everything eastward through Thursday.
A breezy westerly wind may be found on Thursday, with
temperatures cooler and in the 60s. There could also be some
shower and thunderstorm chances in the north. A broad trough
over the region could bring more showers and thunderstorm
chances on Friday. A lack of instability will limit the severe
weather threat. Unsettled westerly flow then looks to be found
through the weekend. Chances for showers and thunderstorms will
be isolated on Saturday, then could return to scattered on
Sunday. Temperatures look to warm each day, with highs
approaching 80 degrees on Sunday. Friday morning could see some
cooler low temperatures, with the weekend looking to see lows
more near normal.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 948 PM CDT Tue May 28 2024

VFR conditions are forecast to prevail across western and
central ND through the 00 UTC TAF cycle. Surface high pressure
over eastern ND will move eastward overnight, with winds becoming
southeast. Winds will increase Wednesday with gusts up to 35 kt
common at all terminals after 18 UTC. Odds of any stratus or fog
development tonight and Wednesday morning in the southeast wind
flow are less than 10 percent, though. We expect thunderstorms to
develop late Wednesday afternoon along the North Dakota-Montana
border, but the probability of them impacting any TAF site before
00 UTC was too low for inclusion in the current TAF forecasts.

&&

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

&&

$$

UPDATE...CJS
DISCUSSION...Anglin
AVIATION...CJS