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182
FXUS63 KBIS 210915
AFDBIS

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

.KEY MESSAGES...

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- Scattered showers and isolated thunderstorms today with the
  best chances (40 to 60%) along and south of the I-94 corridor.

- Chance of showers (20-30%) tonight, possibly a thunderstorm
  west.

- Chance of showers and thunderstorms (20% south to 60% north)
  Saturday. A few afternoon or evening storms over central North
  Dakota could be strong to severe with quarter sized hail and
  60 mph winds.

- Seasonable temperatures north to cool south today, then
  warming through the weekend. Temperatures top out in the 80s
  north to lower 90s south on Monday, then cool slightly through
  mid-week.
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&&

.DISCUSSION...
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Issued at 144 AM CDT Fri Jun 21 2024

Currently, high pressure was situated over the Northern Great
Lakes Region with low pressure over the Central Rockies. A
stationary front extended east from the Rockies across Nebraska
and into Iowa. This has been a focus for thunderstorms with
heavy rain across northern Nebraska and especially southern
South Dakota.

Across the forecast area early this morning, lower level clouds
were increasing across the southwest and south central and high
clouds were increasing over the area from the south and west.

Convection over northeast Montana and far northwest ND last
evening has lifted into Saskatchewan and is no longer expected
to impact the northwest. Farther south, sporadic light
reflectivities were trying to lift from SD into southern ND.

Low stratus and some reductions in visibility were noted at
Hettinger and Dickinson.

For today, a chance of showers remains mainly across the south
half of the forecast area, and especially along and south of
I-94. The past two days models have been too aggressive pushing
precipitation into North Dakota. Since arriving tonight, CAMS
have also bee to quick to lift warm advection precipitation into
the state. SPC mesoanalysis shows strong warm advection lifting
from Nebraska into south Dakota with a strong low level jet
pushing northward. Strong low level moisture transport is also
indicated pushing north through South Dakota. Not sure what the
reason (sure there`s more than one) but this strong warm
advection looks to peter out and if anything, push more off to
the east rather than continuing it`s northward track into ND.
There is surface high pressure situated from the Northern Great
Lakes, westward into North Dakota. Although this high pressure
weakens through the day, this east to west ridge axis remains
over the area. Aloft, a broad southwest flow remains over the
area, but back over the southwest U.S. there is a digging upper
level trough. The surface low pressure mentioned earlier over
the Central Rockies, pretty much remains over this area through
the day today and the strong 850 mb jet from Nebraska into
southern South Dakota pretty much remains stationary through the
day, never lifting into North Dakota. With all that said, it
remains quite uncertain as to what extent precipitation actually
makes it into the area. Plus, we will remain cloudy today and
although bulk shear remains strong, instability is meager at
best.

We do see a wave propagating through the broad southwest flow
from the Northern/Central Rockies early this morning, into the
local area this afternoon. CAMS have been consistent in
developing convection over northern Wyoming/southeast Montana
today and tracking into the western Dakota and across mainly
the southern half of the forecast area. Convection is already
noted across northern portions of Wyoming and into southeast
Montana. Perhaps we see some shower activity work it`s way into
the far south central/James River Valley today, but this
secondary wave from the northern Rockies looks to bring the
better chances for showers and possibly some thunderstorms. CAMS
have been excited at times with the convection moving into the
west today, but given the lack of instability anticipated, the
threat for strong to severe storms looks to be low. In fact, SPC
has pushed the marginal risk that was in the far
southwest/south central, farther south. I`m even a little
hesitant in any thunderstorm activity today, although there is
some elevated instability over western ND this afternoon.
Needless to say, we tried to limit pops from the previous
forecast and also qpf. We still have some 40-60 pops along and
south of the Interstate today, but if the shower activity over
SD doesn`t reach the state and if the aforementioned Nrn
Rockies wave doesn`t result in shower activity pushing into the
area, later shifts will need to continue to lower pops.

Any shower/thunderstorm activity is expected to taper off this
evening. A separate northern stream shortwave currently
tracking across northern Idaho will make its way across northern
Montana today and by late tonight will be approaching western
ND with the potential for showers and thunderstorms moving into
northwest ND.

On Saturday this shortwave will continue tracking across
southern Canada but will begin wrapping around a closed upper
circulation to its north. This lobe will track from southeast
Saskatchewan into southern Manitoba with an attendant surface
trough tracking west to east across North Dakota. Abundant 0-6km
bulk shear remains situated over the area and there should be
enough forcing from the wave and instability due to daytime
heating to produce isolated convection. This convection would
be favored along the Canadian Border, but could extend south
along the surface trough to around the I-94 corridor. SPC has
introduced a marginal risk of severe storms over portions of
western and central North Dakota Saturday. The main threats
would be wind to 60 mph and quarter sized hail.

Once this wave tracks off to the east Saturday evening, we see
upper level ridging build over the area, limiting convection but
allowing warm temperatures to lift northward into the forecast
area. Highs on Sunday will climb into the 80s over western and
southern portions of the forecast area. By Monday, 80s are
expected across the forecast area, with some lower to mid 90s
far south. It`s possible we see some overnight convection late
Sunday evening into Monday as another northern stream wave
flattens the upper level ridge with convection dropping
southeast from Canada possibly clipping northern and eastern
portions of the forecast area. After Monday we see temperatures
drop back into the 70s north to 80s south through the remainder
of the forecast period with maybe a hit or miss thunderstorm.
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&&

.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.

&&

$$

DISCUSSION...TWH
AVIATION...TWH