084
FXUS63 KBIS 191749
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1249 PM CDT Sun May 19 2024

.KEY MESSAGES...

- Low rain shower chances (20 to 30 percent) lift south to north
  this morning.

- Isolated to scattered severe storms late this afternoon
  through the evening from the Standing Rock Reservation to the
  southern James River Valley. Expected hazards include large
  hail to ping pong ball size and damaging wind gusts to 70
  mph, with a tornado or two possible.

- Below normal temperatures with daily chances for rain this
  coming week through the upcoming holiday weekend.

&&

.UPDATE...
Issued at 1227 PM CDT Sun May 19 2024

A warm front continues to lift north across South Dakota, which
can be observed on visible satellite imagery along the cloud
shield near the South Dakota/North Dakota border. This boundary
should continue lifting north, promoting clearing to it`s south
as it does. There is a rather dense area of high clouds
currently located over western North Dakota, however it is
fairly narrow at the moment and fast moving. Will be be able to
clear out enough for robust surface based convection in North
Dakota? We will have to see how things evolve over the next few
hours but that`s the big question. CAMs continue to show storm
initiation in the 21z to 23z time frame over the south central
North Dakota with the strongest UH tracks near the South Dakota
border. Some CAMs have also started to pick up on a strong cell
or two coming out of Montana into west central North Dakota
around the same general time. SPC has expanded the Marginal
Risk (level 1 out of 5) west and north to account for this
potential activity.

UPDATE
Issued at 945 AM CDT Sun May 19 2024

Showers are now located from around northern Stutsman and Foster
counties, up into the north central and northwest. These showers
should continue to be fairly light as they drift east northeast,
maybe amounting to a few hundredths of rain at most. We have
also started to see some clearing across the southwest and parts
of the south central over the last couple of hours. This will
have an impact on severe weather potential later this afternoon
and evening, especially if we can get some more clearing further
east before peak heating. No major changes were needed for this
update. Just blended in the latest observations to the going
forecast.

UPDATE
Issued at 620 AM CDT Sun May 19 2024

Showers continue to lift northeast across the forecast area. We
received a hundredth of an inch /0.01/ at the BIS ASOS from 1 am
through 6:30 AM. We made some minor adjustments to sky cover
and pops based on the latest radar and satellite imagery.
Otherwise no changes to the forecast this morning. Updated text
products will be transmitted shortly.

&&

.DISCUSSION...
Issued at 152 AM CDT Sun May 19 2024

Currently, a broad area of high pressure extended from eastern
Montana, south and east across western and central North Dakota
and into southern Minnesota. Low pressure was situated over the
Northern/Central Rockies, ahead of an advancing upper level
trough over the Pacific Northwest.

This morning, cyclogenesis over the Central High Plains and
shortwave energy lifting northeast through a broad southwest
upper level flow will result in increasing mid level cloudiness
and isolated to scattered showers as a result of increasing
warm advection and mid-upper level forcing. Clouds are already
increasing along the ND/SD border with convection noted in north
central South Dakota. The main question this morning will be how
widespread will shower activity be as it lifts northward through
the forecast area. Forecast sounding indicate that as the cloud
cover lifts north the threat for thunder will diminish. For now
have not added thunder to the forecast through the morning, but
will monitor. Soundings also indicate that the potential for
shower activity looks a little better as forcing lifts farther
north. We utilized a blend of short term guidance to tone down
the potential (mainly 20%) for showers as the activity lifts
north this morning, then a little better chance later this
morning into this afternoon across the north (20-40%).

This afternoon, surface low pressure exits into the plains with
a surface low developing over western South Dakota. Continued
warm advection with and increasing southeast surface flow will
result in an increasingly moist and unstable but capped
atmosphere developing over South Dakota and into southern North
Dakota. Shortwave energy tracking through the upper level trough
will approach the area this afternoon which should eventually
provide the forcing to break the cap and initiate convection
over the western Dakota, and also farther south into the Central
Plains.

There looks to be a fairly small area in south central North
Dakota which could see strong to severe convection this
afternoon. In general, from Grant and Sioux Counties east
through Lamoure and Dickey counties in the southern James River
Valley. As you go north of this area, the thermal profile
quickly becomes unfavorable. SPC has a marginal risk of severe
weather within this area, and a nose of slight risk extending
from the Central Plains north through central South Dakota and
into far south central ND (McIntosh and portions if Emmons
counties). The marginal risk does poke up into far southern
portions of Morton, Burleigh, Kidder and Stutsman counties, but
at this time it looks like the main threat will be more along
the North Dakota/South Dakota border and southward.

Looking at some of the short term guidance, if we see a period
of sunshine over south central ND after the mid level clouds
lift north, we could possibly reach or exceed our high
temperatures guidance, adding to the instability. An afternoon
sounding near Lemmon SD indicates over 60 knots of bulk shear
with a MU CAPE of 500-1000 J/K. The storm mode could potentially
be discrete with an inverted trough poking into south central
ND and nearly perpendicular bulk shear. Storm mode could also
be more of a messy to linear type as with an east-west boundary
along the warm front, situated along the ND/SD border. If we
would happen to get an initial discrete thunderstroms over the
far south central, we could definitely see golfball sized hail
and potentially a tornado. Low level shear looks more favorable
for discrete storms early on (early to mid afternoon) with
shear profiles transforming more into a straight line hodograph
(mid to late afternoon) towards 00Z UTC. With the more linear
type convection the hail size would not be as large, tornado
threat lower and an increase in wind damaging wind speeds. For
our hazards we will include all three, but with what we think is
a favoring for linear mode, we will hedge towards higher winds
and slightly lower hail than for discrete cells. We will message
winds to 70 mph, ping pong ball sized hail and possibly a
tornado or two. We should mention that although initially dry
conditions in the low levels, we see a rapid increase in
moisture with high pwat air and low LCL`s developing along the
ND/SD border.

Some failure modes include the southeast surface flow and the
potential for temperatures that do not reach our forecast
highs, thus lowering the instability. If the surface low over SD
is a little farther south, we could even get more of a east to
northeast surface flow over south central ND, also lowering
instability. I hate to say that our moisture is robbed by
convection farther south, but perhaps it may be displaced some.
There is a MCS currently tracking across NE/KS. There is also a
moderate risk of severe weather over Kansas this afternoon and
evening which could have an eventual impact on how things
develop up in our neck of the woods. I could definitely see a
can in which the strong convection doesn`t quite make it into
ND. Nevertheless, those in the south central portion of the
state should be weather aware this afternoon and evening.

Although we aren`t focusing on the north as much, there is also
a northern stream wave that will keep a risk of general
thunderstorms tonight across all of western and central ND. The
threat for severe storms though is definitely over the south.

Once convection ends tonight it looks like we will have a break
in convection on Monday. Beyond Monday we will continue to see
an active pattern over the region. However, closer to home,
it`s possible many areas could see drier conditions over the
first half of the week, with an upper low to our north and a
more southern track to waves moving through the mean flow. A
Tuesday-Wednesday system may only clip, or even miss the
forecast area. With that said we will remain within a broad
southwest to, at times, a slightly cyclonic upper flow so an
isolated shower/thunderstorm can not be ruled out each day. The
latter half of the work week could then see the next wave
provide more than just a glancing blow. This of course is well
towards the end of the extended period with much uncertainty. We
will remain cool through the upcoming work week with highs
mainly in the 60s, and even some mid and upper 50s. Overnight
lows will be mostly in the 40s, but some upper and even mid 30s
can`t be ruled out.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1227 PM CDT Sun May 19 2024

VFR conditions will prevail through the first part of the period
at all sites. However, chances for showers and storms will
increase late this afternoon and into the evening hours,
especially across the south central and into the James River
Valley. This activity also may usher in some MVFR or low VFR
ceilings to areas across the central and east, including KBIS,
KJMS, and KMOT. Some guidance is a bit more bullish on potential
IFR ceilings over the south central and James River Valley by
late tonight or early Monday morning, but this is a low
confidence solution at the moment. Thus, we will leave it out
of any site specific forecast for now. A few strong to severe
storms will be possible across southern North Dakota. The
strongest storms are likely to be mainly along the South Dakota
border but KBIS could see a storm in the vicinity and KJMS has a
better chance of a storm actually moving overhead. Further
north, a few scattered showers will be possible. Winds may
become gusty and erratic in and around thunderstorms.

&&

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

&&

$$

UPDATE...ZH
DISCUSSION...TWH
AVIATION...ZH