766
FXUS63 KBIS 210539
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1239 AM CDT Fri Jun 21 2024

.KEY MESSAGES...

- Isolated to scattered showers and thunderstorms possible
  tonight.

- Patchy to areas of fog possible tonight, especially along and
  south of Interstate 94.

- Widespread showers and scattered thunderstorms are expected on
  Friday, with a Marginal Risk (level 1 of 5) for isolated
  severe storms over portions of the far southwest and far south
  central.

- Showers and thunderstorms will diminish through Saturday
  morning, with continued daily chances for showers and
  thunderstorms into the middle of next week.

- Temperatures will continue warming through the weekend, with
  expected highs on Monday in the mid 80s to lower 90s.

&&

.UPDATE...
Issued at 1227 AM CDT Fri Jun 21 2024

We kept a slight chance for thunder in the northwest for a few
hours with the ongoing convection over northeast Montana and
southern Saskatchewan. It looks unlikely that convection will
make it into ND but can`t rule it out. Otherwise we removed
thunder from the forecast tonight and limited pops to slight
chance. Cams have shower activity over SD too far north and
think it`s unlikely it will make it into ND overnight, or
possibly tomorrow in many areas as well, but we`ll get to that
later. Updated text products will be transmitted shortly.


UPDATE
Issued at 955 PM CDT Thu Jun 20 2024

Mainly some minor updates to PoPs based on current radar trends
were done late this evening. Showers and thunderstorm chances in
southern portions were delayed until later tonight as a bulk of
these showers are currently located in South Dakota. Also
reduced thunderstorm chances in the northwest and north central
through the late evening hours as storms in Montana have been
diminishing as they approach the ND/MT border. With the sun now
setting, the threat for severe weather through the rest of the
night is low. There is some increasing confidence in fog
development, mainly across the south, tonight especially if
precipitation delays. For now kept mention of fog to patchy
although something to monitor throughout the night.

UPDATE
Issued at 650 PM CDT Thu Jun 20 2024

Limited changes needed early this evening. Currently monitoring
some thunderstorm in Montana, however, as these storms push east
they appear to be weakening. That said, there still remains a
window this evening of generally uncapped 1000 J/KG CAPE and 40
to 50 KTS of 0 to 6 KM shear across the northwest and north
central. The lift along the boundary these storms could from on
appears to be limited yet present. Thus there cold be an
isolated strong to severe storm threat in these areas this
evening. Otherwise look for isolated to scattered showers though
the night. Hi-res models picking up on the potential for fog
tonight into Friday morning, mainly along and south of
Interstate 94. Winds may stay steady through the night which may
hinder this, or help advect in increase moisture and help fog
formation. For now have added in some patchy fog mention to
account for this potential.

&&

.DISCUSSION...
Issued at 247 PM CDT Thu Jun 20 2024

Precipitation has been slow to arrive today, with very few radar
returns in the northwest and southwest. There may be a few drops of
rain reaching the ground in these areas, but it seems rather
unlikely at this point. Surface high pressure dominates north of the
International Border, with a weak pressure gradient across most of
the state. Southwesterly flow aloft continues, with a weak embedded
impulse moving through the flow to our south, across South Dakota.
Convection is ongoing in that area, with the expectation that this
convection won`t move north into North Dakota. The SPC has
introduced a Marginal Risk (level 1 of 5) to eastern Montana, but
this risk stops short of the North Dakotan border. As such, we can
really just expect to see some showers and an occasional
thunderstorm in the northwest and south today and tonight, with the
greatest chances for thunder being in the northwest, aligned with a
narrow corridor of MUCAPE near 1500 J/kg and 0-6 km bulk shear of
around 40 to 50 kts. Severe weather is not anticipated at this time,
though some storms that perfectly ride the CAPE boundary may see
some small hail.

After a brief break in precipitation overnight, chances begin to
move back into the area from the south on Friday. An upper level
trough positioned across Alberta is expected to dive south through
Friday, helping drive some more embedded shortwaves across the
Northern Plains. A surface low across eastern Wyoming and western
South Dakota is expected to deepen and track northeastward through
Friday, helping push that precipitation northward. At the moment,
chances for precipitation range from 40 to 70 percent, with the
highest chances expected during the late evening and early overnight
period. Similar to today, we are anticipating most of this to be
showery, with some isolated thunderstorms. However, this time the
SPC has outlined a Marginal Risk (level 1 of 5) for the very far
southwestern corner of the state, as well as right along much of the
border with South Dakota. There`s a very narrow corridor of MUCAPE
near 1500 J/kg in this area, combined with 0-6 km bulk shear values
nearing 50 kts. The setup just outside of our area is a bit more
potent, which may result in greater chances of storms forming
outside of our area, riding the CAPE boundary and intensifying as it
approaches our border, and briefly being able to sustain itself and
potentially strengthen once they enter North Dakota. However, given
how borderline the event is to begin with, the chances for anything
being severe within our area is still rather low, but also still non-
zero. Given the quick reduction in instability and shear as you move
east, any thunderstorm that forms across much of the rest of our
area is not expected to become severe.

As the aforementioned upper level trough continues moving east, we
are expected to enter a slightly drier and warmer pattern, with a
fairly pronounced ridge building into our west. While temperatures
today and Friday are expected to be slightly below normal, we can
expect to see a quick warmup into the mid 80s and lower 90s by
Monday, which is also expected to be the warmest day of the forecast
period. Chances for precipitation will be on and off, with 15 to 30
percent chances for showers and thunderstorms on Monday, and 10 to
15 percent chances for showers each subsequent day. Due to how warm
it will be, and with the continued southerly flow bringing in decent
moisture over the next few days, instability values will support at
least isolated thunderstorms associated with these showers each day.
The shortwaves embedded within the upper level flow that will bring
these chances each day are not very strong, given the more west-
northwesterly flow aloft, so the exact positioning and timing of
these waves of precipitation are not well resolved from Monday
onward. Tuesday will see a slight reduction in temperatures,
dropping into the upper 70s to lower 80s, and with the upper level
pattern remaining largely the same, these high temperatures are
expected to remain consistently within this range through at least
the end of next week. NBM spreads are somewhat high, owing to the
confidence in this pattern holding true, so we can expect to see
similar conditions from Tuesday onward to at least next Friday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1227 AM CDT Fri Jun 21 2024

MVFR to possibly IFR ceilings and possibly some MVFR vsbys
south.

MVFR cigs to begin the 06Z TAF period at KDIK, otherwise VFR.
MVFR ceilings are expected to lift north from SD into North
Dakota through the overnight hours and expect MVFR to at times
IFR ceilings through much of the day Friday. Shower and possible
thunderstorm activity will also lift north into ND, but there is
much uncertainty as to whether this will make it up to the TAF
sites. Convection could also track west to east over the
southern TAF sites during the day Friday. For now, kept only a
period of VCTS and some VCSH as uncertainty in timing is high.
Also kept ceilings mainly MVFR for not although guidance shows
widespread IFR. IFR vsbys are possible, but WSUP IFR
probabilities are generally around 30 percent along the I-94
corridor. Genially an easterly surface flow is expected through
the TAF period.

&&

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

&&

$$

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