Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 110521

Area Forecast Discussion
National Weather Service Bismarck ND
1221 AM CDT Sat Jul 11 2020

Issued at 1218 AM CDT Sat Jul 11 2020

Decreased precipitation chances a bit through the rest of the
night as development along the front is minimal.Otherwise, no
major changes.

UPDATE Issued at 1003 PM CDT Fri Jul 10 2020

Allowed Severe Thunderstorm Watch number 352 to expire as planned
at 03Z.

Currently, frontal boundary extends from northwest to southwest
North Dakota. As the front continues to push east, isolated to
scattered thunderstorms will be possible from central to east
overnight tonight. With strong deep layer shear (especially across
the southern half) and steep mid-level lapse rates still in
place, some convective cells may become strong. However given lack
of greater theta-e source, the severe risk is low.

Issued at 848 PM CDT Fri Jul 10 2020

Water vapor imagery shows the dry slot of a potent mid-level
shortwave moving over west-central North Dakota with
showers/thunderstorms along the associated cold front currently
moving through Williams/Divide counties. Wind gusts have remained
sub-severe in this area of lesser instability.

Further south, isolated thunderstorms continue as a 500mb jet
streak pushes east over central North Dakota. With steep mid-level
lapse rates still in place across the south and an open 700mb wave
still to pass, isolated thunderstorm development will continue to
be possible across western/central North Dakota through the next
several hours.

UPDATE Issued at 720 PM CDT Fri Jul 10 2020

Quick update to add Logan and McIntosh counties to the severe
thunderstorm watch.

Issued at 559 PM CDT Fri Jul 10 2020

Severe thunderstorm watch number 352 remains valid with this
product issuance.

Storms continue to flare up across eastern Montana and the western
Dakotas ahead of a potent mid level S/WV now over northeast
Montana, projected to slowly push across northern North Dakota
tonight. Main update with this product issuance was to speed up
the eastward progression of showers/storms a bit with current
activity moving east faster. Sky cover was also increased with a
BKN-OVC anvil shield across the area. Other updates were minor
and based mainly on latest obs and trends.


.SHORT TERM...(This evening and tonight)
Issued at 145 PM CDT Fri Jul 10 2020

Thunderstorms, some severe, are expected to move into western
North Dakota this afternoon and progress into the central later
this evening. The greatest chances for very large hail and
damaging wind gusts will be in the southwest to south-central,
however there is still a severe storm threat as a front moves
through the northwest this evening. A Severe Thunderstorm Watch
has been issued for western and much of central North Dakota to
cover these threats.

At 19Z, a frontal boundary was placed north-south across far
eastern Montana with convection developing along in in southeast
Montana. Surface dew points in southwest North Dakota have been
slowly creeping up early this afternoon, currently in the low 60s
at several ASOS/NDAWN reporting sites. Beneath very steep mid-
level lapse rates of 8+ C/km advecting into the southwest, MLCAPE
values in the 2000-3000 J/kg range are forecast to develop.
Strong, line- orthogonal, shear vectors of 45-55 kts will combine
with a slowly uncapping atmosphere to provide a parameter space
for very large hail and damaging wind gusts. However there could
be a competing factor for the eastward progression of the severe
threat in the marginal boundary layer dew points currently
present. Forecast soundings indicated a capping inversion that
would require richer moisture advection to overcome. Upstream dew
points in north-central South Dakota (MBG/PIR) have risen into the
mid 60s, which may be enough to sustain a severe threat into the
south-central later this evening as moisture continues to push

A second uncertainty in this event lies in storm mode, especially
now with initial convection moving through southeast Montana. If
thunderstorms moving across the western border can remain discrete,
the primary threat will be for very large hail and locally
damaging wind gusts. Then downstream, given the eastward
progression of the initiating boundary and unidirectional
hodographs suggesting splitting and interacting storms...upscale
growth into more of an organized wind threat may be possible, more
likely in the south- central portions of the state.

Further north, in the northwest portions of the state, instability
decreases but is still adequate combined with the strong shear
for possible severe storms this evening.

.LONG TERM...(Saturday through Friday)
Issued at 145 PM CDT Fri Jul 10 2020

Near daily chances for showers and thunderstorms highlight the
long term forecast through much of next week.

By Saturday morning, the surface front should have passed through
the James River Valley and Turtle Mountains as the upper level low
begins to shift to the southeast. Showers and possibly low-topped
thunderstorms may linger in the Turtle Mountains and JRV areas
through a portion of the day with a maintenance of moderately
steep low level lapse rates amid cold air advection aloft. Highs
should be relatively cool, in the upper 70s to low 80s.

Ridge builds over the Northern Plains on Sunday as a larger scale
trough approaches from the west. Temperatures warm into the 80s with
low 90s in the southwest. A cold front should arrive in the west
Sunday evening. While strong deep layer shear and steep mid-level
lapse rates will be present, boundary moisture return will likely be
lacking for widespread surface based convection. Forecast soundings
show a capping inversion which seems likely given the thermal ridge
in place as well. However there may be a couple windows for stronger
convection, first in the far southwest where boundary layer moisture
could be adequate for overcoming the cap in the early evening. The
second question will be strength of convection as it moves east
overnight. 12Z GFS/NAM indicate a LLJ may sustain an elevated inflow
layer amid steep mid-level lapse rates and around 50 kts of deep
layer shear. If the LLJ can provide enough low-mid level theta-e
advection, strong to possibly severe thunderstorms may be possible
late Sunday night and early Monday morning. Then frontal boundary
should be pushing east through Monday as a stronger mid-level
shortwave approaches. Boundary layer moisture increases across the
central and east with strong deep layer shear in place. Severe
potential Monday afternoon/evening will depend on daytime heating as
convection may still be ongoing from earlier in the morning.

Precipitation chances after Monday become less clear as the 00Z/12Z
global model set continue to advertise a broad cyclonic trough over
Canada with differences in how the ECMWF/GFS handle the circulation
amplitude and frontal intrusions. While there are at least some
areas of slight chance PoPs in the blended forecast daily through
the week, they will depend on subtle wave timings that are difficult
to resolve at this point. This cyclonic flow should keep highs
mostly in the upper 70s to 80s each day.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1218 AM CDT Sat Jul 11 2020

VFR conditions expected with the exception of KMOT during the
early morning hours. Some MVFR stratus is likely to push down out
of Canada and impact KMOT. Lingering clouds and precipitation
across the east on Saturday.




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