214
FXUS63 KBIS 250607
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
107 AM CDT Tue Jun 25 2024

.KEY MESSAGES...

- Scattered showers and isolated thunderstorm are possible across
  far southern North Dakota tonight. The threat for severe
  weather is low.

- A drier and quieter middle of the work week is expected, with
  mostly clear skies and highs in the 70s and lower 80s on
  Tuesday and Wednesday.

- Medium to high chances (ranging from 60 percent south to 80
  percent north) for showers and thunderstorms Thursday
  afternoon through Thursday night.

- Friday and Saturday will cool further, with highs in the 60s
  north to lower 70s south.

&&

.UPDATE...
Issued at 105 AM CDT Tue Jun 25 2024

Convective development late tonight remains confined to
southeast Montana and northern South Dakota, though satellite
does show increasing mid level clouds from southwest into south
central North Dakota in response to strengthening 700 mb
moisture transport. It remains likely that the strongest
convection will remain well south of the border, but scattered
showers and a few thunderstorms could develop across the
southern tier of counties later overnight into early Tuesday
morning.

The biggest forecast adjustment with this update was to
introduce slight chance (20 percent) PoPs across much of
northern and central North Dakota Tuesday afternoon and evening.
High-resolution guidance has become more insistent that at least
a few showers and storms will form in a low CAPE/high shear
environment, though there is greater ensemble disparity in
timing and placement. The potential intensity of convection
Tuesday afternoon and evening will be discussed further in the
next full forecast package update.

UPDATE
Issued at 950 PM CDT Mon Jun 24 2024

Front has mostly moved through the CWA late this evening.
Chances for thunderstorms along it during the next hour or so now
appear minimal. There is some increasing confidence for chances
for showers and thunderstorms late this evening through tonight
as this front stalls near the SD/ND border. These would be
elevated in nature, although could be in an environment of
up to 1500 J/kg MUCAPE. Shear will remain high at 40 to 50
knots, with the shear vector along the boundary perhaps
promoting training thunderstorms. The threat for severe weather
is still overall low through the night given the elevated nature
and lack of instability with these storms. Although any
isolated stronger storms could still produce hail up to the size
of quarters and wind gusts up to 70 mph based on the high
amounts of shear. For now updated PoPs for tonight based on the
latest hi-res guidance.

UPDATE
Issued at 643 PM CDT Mon Jun 24 2024

Overall the forecast remains on track. A cold front from
Northern Minnesota to south central North Dakota still looks to
be the focus for thunderstorms this evening through tonight as
the front moves eastward. Overall the consensus is low chance
(20 percent or less) for thunderstorms through the evening in
our CWA. The one area to monitor will be the boundary currently
in the southern James River Valley. This boundary is already
producing storms to the northeast. However, our area is more
capped and does not have as good of forcing as the north. Still
there is a small window between now and sunset a thunderstorm
is possible, perhaps becoming strong to severe quickly.
Confidence in these storms developing in our CWA is low,
although maintained slight PoPs through the evening in this
mentioned area.

&&

.DISCUSSION...
Issued at 254 PM CDT Mon Jun 24 2024

Currently, mostly clear skies are present across western and central
North Dakota, with a few high cirrus streaming into the northwest,
and some fair weather cumulus across the south central.
There were some billow clouds in the south central earlier as
well, but they have since eroded away, indicating the
possibility that the boundary layer is beginning to destabilize
across the south central, especially in the southern James
River Valley. There was a single little clump of cells
attempting to strengthen in western Stutsman County about an
hour ago, with a few attempts looking pretty decent in terms of
reflectivity. Each subsequent attempt resulted in better looking
updrafts and higher reflectivity values, but it was just a bit
too narrow for it to really sustain itself, and within the past
30 to 60 minutes it has completely fallen apart. Lightning was
also analyzed in this storm, showing up after a few attempts,
but overall, the storm kept weakening before becoming anything
strong, before it would attempt to strengthen again.

While these storms failed, it was interesting to see how quickly it
seemed to overcome the cap that had been in place. The environment
within this area is absolutely worthy of supporting some strong to
severe storms, with deterministic MUCAPE values exceeding 3000 to
4000 J/kg as a result of the very warm and moist environment. 0-6 km
bulk shear isn`t as high, with values only in the 30 to 40 kt range,
but its certainly still supportive. As a result, the SPC kept much
of our far eastern portions within a Marginal Risk (level 1 out of
5), supporting isolated strong to severe storms through this
evening. However, the main concern from previous forecasts has been
the strength of the cap across the area. Initially, we had been
anticipating the cap to be very strong, which would help subdue most
attempts of convection. If anything managed to break through later
this evening, we would anticipate quick growth into a strong to
severe storm, but CAMs have not been resolving really any convection
in the area whatsoever. The fact that there has already been a storm
strong enough to start intensifying has suggested that the cap may
not be as strong as initially thought. It is still certainly strong,
but definitely worth following closely, in case more signs begin
to point towards it weakening.

Something else we`ve noticed has been the presence of some sort
of boundary, stretching roughly west to east from southwestern
Kidder county, through central Stutsman county, and into Barnes
and Cass counties within Grand Forks` forecast area. This cell
formed on the western half of this boundary, which leads us to
believe that this may have been a residual, slow moving outflow
boundary from the convection earlier this morning. We`ll
continue to monitor how both this boundary and this storm
develop, but if this boundary can sufficiently help erode the
cap as it slowly wanders east southeast, we may see more
attempts at convection strong enough to overcome the cap and tap
into the potent instability across the southern James River
Valley this evening. Given that instability is expected to
decrease quite a bit later this evening, the threat for severe
weather isn`t expected to last long. Temperatures today continue
to climb, with many places in the south approaching the upper
80s. Some places may briefly see 90 degrees, which combined with
dew points in the mid 60s to lower 70s, may make it feel even
warmer than 90.

The middle of the work week is expected to be a bit quiet, with
temperatures on Tuesday and Wednesday forecast to largely be in the
70s, with lower 80s possible in the southwest. Aloft, zonal westerly
flow will be present through Wednesday morning, before shifting to
be more northwesterly Wednesday night. Minimal precipitation chances
are expected during this time, as well as generally clear skies, as
surface high pressure from southern Saskatchewan and Manitoba slides
southeast across North Dakota. It might be a bit breezy in the north
on Tuesday as well, as the pressure gradient deepens a bit with the
approach of the surface high. All in all, a generally quiet period
is expected from tonight through Wednesday evening.

Late Wednesday night sees the arrival of our next wave of
precipitation chances. Flow aloft becomes a bit more disturbed and
out of the southwest early Thursday morning, as a deep trough across
the Pacific Northwest deepens and moves east into the northern High
Plains. The attendant surface low is forecast to deepen and move
east through South Dakota, resulting in wraparound moisture
filtering into North Dakota and bringing about a good amount of
rain. Current long range guidance suggests PWAT values within the
90th to 95th climatological percentile for PWAT values at
Bismarck (roughly in the 1.1 to 1.3 inch range), with a few
areas potentially even higher than that, which indicates that
any showers and thunderstorms that develop will be very
efficient producers of precipitation. It`s also worth noting
that the NBM PoPs have already begun to advertise widespread 60
to 80 percent chances for showers and thunderstorms on
Thursday. This could also be our next wave of severe weather as
well, with long range deterministic guidance also indicating
favorable conditions for all hazards. CSU machine learning
guidance continues to advertise the potential for severe weather
across much of our western and central areas as well.

Temperatures on Thursday will remain warm, with temperatures ranging
from the 70s in the northeast to the lower 90s in the southwest. As
the system moves through on Friday and Saturday, highs will cool
quite a bit, with highs on Saturday only in the 60s for much of the
area. Precipitation chances decrease and temperatures increase once
more heading into the start of next week, with zonal flow aloft and
ridging arriving from the west once again.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 105 AM CDT Tue Jun 25 2024

VFR conditions are likely to prevail through the forecast period.
There are low chances for showers and thunderstorms across northern
and central North Dakota this afternoon and evening. Light winds
overnight will become northwest around 12-17 kts on Tuesday,
strongest across the north.

&&

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

&&

$$

UPDATE...Hollan
DISCUSSION...Besson
AVIATION...Hollan