035
FXUS63 KBIS 210309
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1009 PM CDT Sat Jul 20 2024

.KEY MESSAGES...

- Isolated to scattered thunderstorms are expected on and off through
  Monday. The threat for severe weather remains low.

- Smoke aloft from distant wildfires will be found through the
  weekend (at least).

- High temperatures will mainly be in the 80s through Monday,
  while some 90s will likely return mid to late week.

&&

.UPDATE...
Issued at 958 PM CDT Sat Jul 20 2024

Storms continue to push south along a line from eastern Sheridan
county, down to northeast of Pingree in Stutsman county. A few
of these cells have perked up to near severe limits with the
potential for hail up to the size of nickels and winds to
around 40 mph or so. It seems that these storms have moved into
a pocket of marginally better effective shear at around 25
knots. With capping starting to settle back in, minimal forcing,
and shear dropping off quickly, we expect there should be a
weakening trend here over the next hour or two. We did go ahead
and update precipitation chances through the night based on the
latest radar observations and guidance trends.

The other main change for this update was to add some patchy
fog to the forecast late tonight into early Sunday morning,
mainly along and north of the Missouri River. The HRRR and RAP
are more bullish than most of the other CAMs regarding fog
development but the environment will be similar to the last two
nights when we had some fairly widespread ground fog at times.

UPDATE
Issued at 625 PM CDT Sat Jul 20 2024

No major changes were needed for this update. Just blended in
the latest observations to the going forecast. Isolated
thunderstorms have developed as expected and should continue
until we lose daytime heating later this evening.

&&

.DISCUSSION...
Issued at 143 PM CDT Sat Jul 20 2024

Broad high pressure was in place over the Northern Plains this
afternoon, with a sharp upper ridge extending through the
Canadian Prairies to our northwest, leading to northerly flow
across the forecast area. A few showers and thunderstorms were
ongoing as of 19 UTC across the south central and southeast,
with plenty of instability available but very low shear, so the
expectation is for pulse type, airmass thunderstorms. CAMs have
been relatively inconsistent in timing and location of any
convection, but have been most consistent in the north central
this evening. Overall, we have broad-brushed low POPs across
most of the forecast area through tonight to account for this
potential, especially with limited forcing aloft to increase
chances in any one place. Flow aloft is very weak, so any storms
that develop will be very slow moving.

This northerly flow is also bringing in large amounts of smoke
aloft from wildfires in Alberta and British Columbia. We opted
to not include any near-surface smoke with this update, as
confidence is not quite high enough at the moment, but we cannot
rule out that some locations could experience minor visibility
reductions at some point. Otherwise, the latest HRRR smoke
forecast shows no reprieve from thick smoke aloft, so
continuing the message of hazy skies through the rest of the
weekend.

A similar day is expected on both Sunday and Monday, with highs
in the 80s, light winds, and chances (20-40%) for showers and
thunderstorms. Sunday`s precipitation might be a bit more
spatially limited, while on Monday, a back door cold front and
attendant upper wave (although relatively weak) will bring
higher chances for showers and thunderstorms during the day.
With continued weak shear, the potential for severe
thunderstorms is very low.

As the upper ridge begins to build and shift to east through the
week, temperatures will start climbing, especially across
western North Dakota. The ridge axis is progged to be overhead
of the Northern Plains Wednesday into Friday, with blended
guidance suggesting these will be the hottest days of the
extended period. Highs around 100 degrees F are within reason
mainly on Thursday, with low to medium probabilities of
exceeding this threshold across western North Dakota, especially
in areas along the Montana state border. Lower dew points are
co-located with these hotter temperatures which is keeping
current forecast apparent temperatures just below criteria, but
this will be something to watch in the coming days. Chances for
precipitation are low Tuesday through Thursday.

Upstream of the ridge, a deep upper low is forecast to move
onshore and into the Canadian Prairies late in the week, pushing
the ridge out of the area. More consistent POPs, although low,
begin showing up during this time, while machine learning
probabilities indicate low but increasing chances for severe
thunderstorms late in the week. NBM temperature percentiles
show that after Friday, temperatures will slowly decrease
through the weekend, although expect highs to stay in the mid
80s to mid 90s.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 625 PM CDT Sat Jul 20 2024

VFR conditions are generally expected through the period.
Isolated hit or miss thunderstorms will continue across western
and central North Dakota through the evening and then again on
Sunday afternoon. If a storm moves overhead, brief MVFR to IFR
visibility reductions will be possible. The isolated nature of
convection precludes mention for any specific site forecast but
any storm that moves overhead could produce brief heavy
downpours and small hail. Winds may also become gusty and
erratic in the vicinity of any thunderstorms.

&&

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

&&

$$

UPDATE...ZH
DISCUSSION...Jones
AVIATION...ZH