538
FXUS63 KBIS 280242
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
942 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- The threat for severe thunderstorms has ended across western
  North Dakota, and has greatly diminished over central North
  Dakota.

- Isolated severe storms remain possible across central North
  Dakota through the early overnight hours. The main expected
  hazard is damaging winds up to 60 mph.

&&

.UPDATE...
Issued at 941 PM CDT Thu Jun 27 2024

The threat for severe storms is quickly diminishing across western
and central North Dakota.

Storm structures per radar analysis have become much less organized
and intense over the past hour, and convection is now moving into a
more stable and weaker shear environment. The highest potential for
a severe storm through 11 PM CDT is from the Standing Rock
Reservation and Cannonball River into western Emmons County where 0-
3 km shear is still as high as 30 kts per SPC mesoanalysis. The
Tornado Watch has been cancelled.

UPDATE
Issued at 718 PM CDT Thu Jun 27 2024

Numerous severe thunderstorms continue across western North
Dakota. Things are progressing about as expected, with a few
initial discrete supercells that had funnel cloud / brief
tornado reports, as well as large hail. Behind these storms, a
significant line of storms has developed and is quickly moving
east, getting quite close to absorbing the initial supercells.
Multiple wind gusts in the 80 mph range have been observed at
mesonet stations, and as this line continues moving east,
expecting damaging wind to be the primary threat with 0-3km
shear in the 30-35 knot range and 900-1000 J/kg of DCAPE. The
expectation is still for the severity of storms to slowly
decrease as it moves east through central North Dakota through
the evening. We do now have a Severe Thunderstorm Watch out for
most of central and parts of northern North Dakota, enclosing
the Tornado Watch, valid until 2 AM CDT.

UPDATE
Issued at 450 PM CDT Thu Jun 27 2024

Update for the issuance of a Tornado Watch for most of western
North Dakota until 10 PM CDT.

&&

.DISCUSSION...
Issued at 207 PM CDT Thu Jun 27 2024

The biggest forecast challenge remains the enhanced risk for severe
weather late this afternoon into tonight.

A warm frontal boundary with a NNW to SSE orientation off east
Montana surface low pressure should trigger thunderstorms late
this afternoon. Initially, this will result in a near
perpendicular orientation of the 0 to 6 km bulk shear and the
frontal boundary. As a result, there will likely be a few
supercells that develop in eastern Montana and/or western North
Dakota late this afternoon. Very quickly, trailing cold frontal
boundary will begin to occlude the front and bulk shear will
switch out of the southwest. This should result in thunderstorms
rapidly becoming clustered and then potentially linear.

All threats remain on the table during the supercell phase. As the
frontal boundary occludes, the triple point is progged to slide
from northwest to southeast mainly across southwestern North
Dakota, or rather, somewhere south and west of the Missouri
River. Or, potentially across far northwestern South Dakota.
The exact path of the triple point is uncertain, however, this
will be the area where tornadoes are most favored to occur as
highlighted by the highest sig tor parameter values. In regard
to very large hail, with a ribbon of instability potentially
reaching as high as 4000 J/kg co-located with 50 kts of 0 to 6
km bulk shear and strong anvil level winds, hail up to the size
of baseballs is entirely possible.

Of note, one major factor also favoring the southwest more so
than the northwest for discrete cells this afternoon is that
thick low level stratus is present over most of the area, except
the far southwest. This will help erode any capping that is in
place. At present, billow clouds are observable on satellite
that highlight things are presently stable with high shear. One
thing we will be watching for is when billow clouds begin to
dissipate and vertical agitation occurs. That will suggest
thunderstorms might fire within the next couple hours.

As storms begin to cluster and potentially line out during the
evening and move towards Highway 83, the tornado threat will
decrease as will the hail threat, although the straight line
wind risk may increase (up to 80 mph gusts possible). Hail up
to the size of ping pong balls and strong winds up to 80 mph are
possible mainly between areas along and east of Highway 83 and
west of Highway 281. As storms approach Highway 281 and areas
east, the threat will become mainly 70 mph winds, perhaps with
hail up to the size of quarters. All that said, there are
questions as to whether or not severe storms will have trouble
penetrating further east tonight, especially for locations east
of Highway 83, due to aforementioned thick low level stratus
that may hinder higher instability.

Conditions should be mostly dry Friday morning before another
shortwave off southern Canadian upper low pressure brings
additional showers and thunderstorms to the area on Friday.
Locations most likely to see additional rainfall Friday are
those in the north. Generally speaking, severe weather is not
anticipated, although there is a marginal risk for Rolette
County and clipping eastern Dickey and Bottineau Counties.
Saturday should then be dry and cold for this time of year with
highs mostly in the 60s. Slightly warmer temperatures are then
expected for next week with highs mostly in the low 70s to low
80s. Showers and thunderstorms are then likely to return by late
Sunday night and into early next week. A few storms may be
severe.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 718 PM CDT Thu Jun 27 2024

Widespread thunderstorms will continue across western and
central North Dakota this evening into tonight. Significant
wind gusts of up to 70 knots are possible within the next few
hours at KDIK and KBIS, and are less likely but still possible
at KXWA/KMOT. TSRA and very large variable wind speeds were
used in TAFs to depict the most likely timeframe for severe
weather at a particular terminal. Across the far north, low MVFR
to IFR ceilings are persistent, with areas of fog leading to
MVFR visibilities. Expecting all thunderstorms to be out of the
area by around 7 or 8Z.

&&

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

&&

$$

UPDATE...Hollan
DISCUSSION...Telken
AVIATION...Jones