967
FXUS63 KBIS 191138
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
638 AM 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 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 /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 620 AM CDT Sun May 19 2024

VFR conditions to begin the 12Z TAF period. Expect mid level
clouds and scattered showers to lift north through the area this
morning. This afternoon into this evening, there will be
lowering clouds north with a hit and miss shower and possibly at
thunderstorm, but too uncertain to mention thunder at this time.
Added a VCSH at KXWA and KMOT after 00 UTC. In the south,
especially from KBIS to KJMS, there will be the potential for
showers and thunderstorms late this afternoon through this
evening. The favored area looks to be south of KBIS so added a
VCTS at 00 UTC. AT KJMS we added a VCTS beginning at 02 UTC with
a TEMPO for a thunderstorm 02-06 UTC. Increasing low level
clouds will also lift into the area with the potential for MVFR-
IFR around KBIS-KJMS and south after 00Z Monday. For now we
included MVFR ceilings at both KBIS and KMOT. It is possible
that MVFR to IFR ceilings become even more widespread but will
limit lower ceilings to these two sites for now. Light winds to
begin the TAF period. Winds will become south to southeast
this morning and then shift east to northeast later in the day
and then north to northwest tonight. Winds generally 10 to 20
knots after mid morning but southeast flow will be on the
higher side of this range by Sunday afternoon.

&&

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

&&

$$

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