692
FXUS63 KBIS 151739
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1239 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Scattered severe thunderstorms are possible across western and
  central North Dakota late this afternoon through early Sunday
  morning. Expected hazards include damaging winds up to 70 mph
  and hail up to tennis ball size, with a tornado or two
  possible.

- The highest risk for damaging winds is across northwest and
  north central North Dakota this evening through early Sunday
  morning, where isolated gusts to 80 mph are possible.

- Isolated to scattered severe thunderstorms are possible across
  south central and southeast North Dakota Monday through Monday
  night.

- Warm and humid today, followed by below normal temperatures
  through the first half of next week. Windy in the northwest on
  Sunday.

&&

.UPDATE...
Issued at 1238 PM CDT Sat Jun 15 2024

There has been a slight uptick in lightning activity with the
showers moving through northwest North Dakota early this afternoon.
These showers and storms should continue to progress northeastward
into southern Canada through mid afternoon. Severe weather remains
unexpected with this activity. Farther south, satellite imagery
shows attempts at convective initiation along an eastward
progressing boundary in southeast Montana. Latest SPC mesoanalysis
indicates weakening SBCIN in southwest North Dakota, so there is
potential for initiation much sooner than previously anticipated.
Should this occur, there is sufficient shear to support a strong to
severe storm in the southwest, but not as much as is forecast for
later in the afternoon and evening.

UPDATE
Issued at 1011 AM CDT Sat Jun 15 2024

A few showers had developed over southern Grant/western
Sioux Counties earlier this morning in a small pocket of 850 mb
frontogenesis, but have since dissipated. Back to the
northwest, an area of rain with occasional lightning continues
to track northeast through northeast Montana. CAMs do not appear
to have a good handle on the current state of this complex, but
extrapolation of current trends would bring it into Williams
and Divide Counties between 11 AM and noon CDT. Any storms with
this activity should not be severe.

There are two notable trends in 12Z CAMs. The first is that there
appears to be a lower probability of convective initiation anywhere
in western and central North Dakota prior to 5 PM CDT, likely owing
to the strength of low to mid level capping. The other more
concerning trend is an increased probability for a higher-end
damaging wind event across northwest and north central North Dakota
from approximately 8 PM to 1 AM CDT this evening into tonight. The
CAPE/shear parameter space looks impressive, with MUCAPE on the
order of 2000-3000 J/kg, 0-6 km bulk shear as high as 60 kts, and 0-
3 km bulk shear as high as 45 kts. The low level kinematic setup is
also favorable, with strong 850 mb poleward moisture transport and
surface to 925 mb winds directly opposing forward-propagating
Corfidi vectors. We will continue with our current messaging of
isolated winds to 80 mph, but will shift to honing in on that
potential across northwest and north central North Dakota after the
regularly scheduled issuance of the SPC Day 1 Convective Outlook
around 1130 AM CDT.

UPDATE
Issued at 640 AM CDT Sat Jun 15 2024

Limited updates needed this morning. The first of two upper
level waves may bring an isolated to scattered shower across
the northwest and north central this morning. Some lightning has
been observed in Montana with these showers, and may also do so
as they traverse North Dakota. A secondary wave combined with a
surface low could then bring strong to severe storms tonight.
Overall made only minor updates this morning and the forecast
remains on track.

&&

.DISCUSSION...
Issued at 430 AM CDT Sat Jun 15 2024

Isolated to scattered severe thunderstorms still expected today
into tonight across portions of western and central North
Dakota. This morning, a low level just could bring a few
isolated thunderstorms to eastern areas, while a developing
surface low and weak wave in southwest flow aloft brings some
showers to the west. Surface low then looks to develop through
the day today, setting up a warm front across much of the state.
High temperatures will rise slightly today as a result, with
some southwestern sites seeing highs in the lower 90s. Southerly
flow at the surface will advect higher dewpoints in today. NBM
forecast afternoon dewpoints in the mid 60s. Perhaps this is a
touch high as dewpoints of this magnitude are as far south as
Nebraska at this time. However, even dewpoints in the upper 50s
to lower 60s combined with strong heating today will bring
abundant amounts of instability with MUCAPE over 2000 J/KG, and
some areas even seeing up to 3000 J/KG. Shear will also be
robust today, with 0 to 6 KM shear up to 50 knots. The limiting
factor during the day will be capping. This breaks down later
this afternoon through this evening when another more potent
shortwave aloft moves through. An isolated severe storm is
possible ahead of this wave, although the highest confidence in
timing for today`s severe weather will be when this mid level
shortwave moves through. Given this the highest confidence in
timing for today`s severe weather is roughly 5 PM to 1 AM CDT.
Storm mode will greatly determine today`s hazards. The shear
vector is generally west to east today, until it becomes more
along the cold front tonight. Thus if storms linger into the
late evening or overnight hours, a linear storm mode can be
expected. However, storms that can go earlier in the evening
have the potential to be discrete or at the very least
multi-cluster. These storms will be the ones to watch for all
hazards. High CAPE and high shear aside, hodographs showing good
veering this evening, giving fair amount of 0 to 1 KM and 0 to
3 KM SRH. STP values over 1 are also found during this time.
LCLs are about 1000 m, which would be adequate for tornado
development. Thus any discrete cell that forms early in the
severe window will have the possibility of creating a tornado or
two. Large hail will also be of concern today given mentioned
parameters. Historical data showing a lot of cases with similar
parameters bringing baseball size or larger hail. Would like to
see perhaps a touch higher shear to have higher confidence in
this larger sized hail. The tornado threat also may tone down
hail slightly. Still decided to raise the max hail size today to
tennis ball size. The wind threat also remains high today. Kept
in 70 mph winds with some isolated 80 mph gusts. This again
goes along with what will the storm mode be. The higher wind
gusts would likely be if severe weather goes later and closer to
the cold front. This timing brings high DCAPE over 1000 J/KG
and 0 to 3 KM shear 25 to 30 knots. MUCAPE could be little
higher for these stronger winds, although will be adequate. Thus
kept wind values messaged as is. Of note too are higher Pwat
values and average storm motions. Thus heavy rain could also be
possible today. Cold front should progress quickly tonight
across the CWA, moving or diminishing severe weather during the
early to mid overnight hours. A switch to westerly winds may
also be found, and they could become breezy at times. Lows
tonight behind this front will be in the lower 50s in the west,
while near 60 degrees can be expected in the east.

A generally post frontal day is then expected for Sunday. Look
for cooler temperatures and breezy to windy westerly winds.
Some areas in the north and west should still be monitored for
potential advisory level winds. SPC maintained a Marginal Risk
for severe weather in southcentral and southeastern portions.
Shear will remain high, although instability looks limited.
Perhaps as the front stalls an isolated severe storm is still
possible in these areas later in the day through the night.
Highs on Sunday look to be in the mid 60s to mid 70s, with some
lower 80s in the far southeast. Lows Sunday night look to be mid
40s to mid 50s. Of note too for Sunday will be lowering RH
values in the afternoon into the 20s. Fuels may still be too
green for fire weather concerns, although breezy to windy winds
and lowering RH could bring at least some increased concerns.
The front remains stalled for Monday, then is reinforced by
another cold front through Monday night. This could bring the
next round of showers and thunderstorms. SPC now has a Marginal
to Slight Risk across central and eastern North Dakota. Shear
will again be high on Monday, although CAPE is somewhat modest
though increased over Sunday. Large hail and damaging winds
right now look to be the main threats. Another post frontal day
could then be found on Tuesday, with further cooling of
temperatures into the 60s. Lingering showers and thunderstorms
may also be found. Tuesday night into Wednesday morning could
then be quite cool for some areas. NBM forecast temperatures are
currently in the 40s for most areas. ECMWF EFI values for Min T
during this time period though are around -0.8. Looking at the
NBM 25th percentile gives some lows in the upper 30s across the
west Wednesday morning. Something to monitor perhaps. A gradual
warmup could then be in store for mid to late next week in a
zonal to perhaps slightly southwesterly flow. Another broad
trough could approach the area mid to later in the week,
returning near daily chances for showers and thunderstorms.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1238 PM CDT Sat Jun 15 2024

Scattered showers and a few thunderstorms will remain possible
across northwest North Dakota early this afternoon, but VFR
conditions should prevail. Later this afternoon and evening,
chances for thunderstorms will increase across western North
Dakota, shifting into central North Dakota later in the evening
and overnight. Some storms could be severe with very large hail
and damaging wind gusts as high as 60 kts. The highest
probability for storms is from northwest to north central North
Dakota during the late evening and early overnight hours. A
TEMPO group has been introduced to the KXWA and KMOT TAFs for
TSRA with IFR visibility and 45 kt gusts. A brief period of
lower ceilings is also possible with any storm. A cold front
trailing the storms later tonight into Sunday morning will shift
winds to the west-northwest around 15 kts. Prior to the frontal
passage, KMOT could have enhanced low level wind shear
overnight.

&&

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

&&

$$

UPDATE...Hollan
DISCUSSION...Anglin
AVIATION...Hollan