436
FXUS63 KBIS 210601
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
101 AM CDT Tue May 21 2024

.KEY MESSAGES...

- Temperatures continue to trend near to below normal this
  week, with highs in the upper 50s to around 70 and lows in the
  mid 30s to upper 40s.

- Expect medium to high chances (40 to 80 percent) for rain in
  the James River Valley on Tuesday, with lower chances
  elsewhere. Winds will also be gusty over portions of the James
  River Valley on Tuesday.

- Widespread medium to high chances for showers and a few
  thunderstorms across all of western and central North Dakota
  Thursday into Friday.

&&

.UPDATE...
Issued at 1259 AM CDT Tue May 21 2024

No significant forecast changes are needed for this update. Isolated
showers in north central North Dakota have dissipated and moved into
southwest Manitoba. Dry weather is expected across our forecast area
overnight, with rain entering the southern James River Valley early
Tuesday morning.

UPDATE
Issued at 952 PM CDT Mon May 20 2024

Little needing update late this evening. A few showers and
isolated thunderstorms remain in the northwest, although
coverage is starting to diminish or move out of the CWA. There
is still an isolated shower or thunderstorm possible into the
early overnight hours, although the chances are starting to
diminish. This wave that brought these showers today may still
linger across the area tomorrow afternoon and evening. Added in
a slight chance for these showers and thunderstorms during this
time period tomorrow across some western and central portions.
Meanwhile, southeastern portions may see some light rain late
this evening into the early overnight hours. Then the next round
of round may move in from South Dakota, which is starting to
take shape in southwestern South Dakota right now. There still
remains uncertainty on exact timing location of this rain for
North Dakota. For now made minimal changes to tomorrow`s
forecast for these areas.

UPDATE
Issued at 650 PM CDT Mon May 20 2024

A few showers have entered into northwestern ND this evening
ahead of an upper level low in southern Canada. These could
lingering through the evening, then diminish shortly after
sunset. Instability is low, although there are some modest lapse
rates in the mid levels. Given the presence of at least small
amounts of instability, there could be an isolated thunderstorm
as well through the evening. Strong to severe storms are not
expected at this time. Otherwise the forecast overall remains on
track. Continue to monitor the progression of rain in South
Dakota. For now it appears dry air is holding off this rain from
entering into ND this evening, although could start entering
into the south tonight.

&&

.DISCUSSION...
Issued at 320 PM CDT Mon May 20 2024

Western and central North Dakota sits under the influence of
southwest flow aloft as a nearly stationary upper low continues
to spin over Saskatchewan. Some diurnal cumulus will continue
this afternoon and into the early evening across much or our
central and east with high clouds streaming into the southwest.
Highs this afternoon will remain cool, generally around or just
below normal for this time of year in the 60s.

Later tonight, a southern stream short wave will eject from a
trough located to our west as a surface low deepens and kicks
out into the central Plains. This low will eventually lift into
portions of the northern Plains as a deformation band of rain
starts to organize to it`s north and west. Low to medium rain
chances (20 to 40 percent) will move into the far south tonight
with medium to high chances (40 to 80 percent) developing across
the James River Valley by mid to late Tuesday morning.
Elsewhere, expect only low chances for an isolated shower or
two. While most of the significant rain will mainly fall to the
south and east of our area, the NBM is suggesting a 30 to 50
percent chance for a half inch of rain or more across the
eastern halves of LaMoure and Dickey counties. Increasing that
threshold to an inch or greater knocks the max probabilities
down into the 10 to 20 percent range. Most of the rain will move
out to the east by Tuesday evening. Winds will also become
gusty out of the north across the James River Valley on Tuesday.
Eastern portions of LaMoure and Dickey counties could see
sustained winds approaching 30 mph and gusts up to 40 mph. It`s
not out of the question that a small Wind Advisory could
eventually be needed across our far southeast but confidence is
not high enough at this time. If the low jogs even slightly
more east, winds would probably end up trending lower.
Precipitation chances would also decrease.

For the most part, we will see a relative break in precipitation
on Wednesday as we transition into low amplitude northwest flow
aloft. Some guidance does bring a weak wave down the ridge
later in the day, leading to some low shower chances (around 20
percent) across most of the west and portions of the central
late afternoon and into the overnight hours. The ridge axis will
then amplify as it crosses the state from west to east on
Thursday with a potent upper trough/low directly on it`s heels.
This feature will be the trigger for our next chance of
widespread precipitation. The upper low moves into the tri-
border region of Montana/North Dakota/South Dakota by late
Thursday, bringing medium to high chances for rain to pretty
much all of western and central North Dakota Thursday afternoon
through Friday morning. We will also see some isolated to
scattered thunderstorms Thursday afternoon and evening with a
low chance for a strong storm or two. Shear will be more than
enough for strong to severe storms but thus far ensembles and
models suggest that meager moisture quality may keep instability
limited. Highs will also only max out in upper 60s and lower
70s across the southern third of the state where storms are most
likely. It is worth noting that both CIPS analogs and CSU
Machine Learning Severe Guidance are now showing at least low
chances for some severe weather so it will be interesting to
follow the trends as we move a bit closer. Precipitation chances
will decrease to the east through the day on Friday. Most
guidance then brings another strong upper low into the region
towards the end of the weekend, leading to more low to medium
chances of precipitation to our forecast area Saturday night
through at least Sunday as an active pattern continues. Quite a
bit of uncertainty remains regarding the track of the late
weekend system but we could also see a slight chance of
thunderstorms as it moves through the region.

Temperatures will generally remain around to just below normal
for this time of year through the forecast period, mainly
ranging from the upper 50s to lower 70s. The coolest days should
be Thursday and Friday when highs may only rise into the low to
mid 50s across the north. There also may be a chance for some
patchy frost during the early morning hours Wednesday through
Saturday as some lows dip into the mid to upper 30s at times,
especially in low lying areas.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1259 AM CDT Tue May 21 2024

VFR conditions are expected through the forecast period. Light rain
will fall over the southern James River Valley later Tuesday morning
and afternoon. The rain could reach KJMS, but categorical
visibility restrictions are unlikely. More widely scattered
showers could develop Tuesday afternoon from around KBIS to east
of KMOT. Northeast winds will increase to around 20 kts at KJMS
Tuesday afternoon, with gusts approaching 30 kts. 10-15 kt
winds are expected elsewhere Tuesday afternoon, with a northerly
direction in central North Dakota and northwesterly in western
North Dakota.

&&

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

&&

$$

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