Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 211139

Area Forecast Discussion
National Weather Service Bismarck ND
639 AM CDT Fri Jul 21 2017

Issued at 635 AM CDT Fri Jul 21 2017

Not much change with this forecast update for today, as the severe
potential remains unchanged, as well as the uncertainty in the
CAMs through the 10 UTC HRRR. Did add PoPs for thunderstorms
across northwest North Dakota this morning. This could be a signal
for an upper level shortwave across eastern Montana that could
yield a round of earlier initiation north central around midday.
However, this remains somewhat uncertain.


.SHORT TERM...(Today and tonight)
Issued at 401 AM CDT Fri Jul 21 2017

Severe potential this afternoon and evening central, and near
critical fire weather conditions southwest highlight the short
term forecast.

See the fire weather discussion below for details regarding near
critical conditions southwest this afternoon and early evening.

Regarding severe convective potential, uncertainty still remains
in how the event may evolve as highlighted by run to run
inconsistencies across the CAMs through the 07 UTC HRRR. However,
the potential for large, destructive hail to 2 inches in diameter
or greater, damaging wind gusts to 75 mph, and a tornado or two
are possible across most of central North Dakota this afternoon
and evening.

A cold front approaching the US Highway 83 corridor around 18 UTC
with a likely pre-frontal trough, with a weak stationary front
across the US Highway 2 corridor will be the surface focal points
for initiation. Aloft, a few weak impulses across southeast
Montana this morning will propagate into south central North
Dakota by midday. A second stronger wave across southern Canada
arrives late this afternoon and early evening along the
international border. A moist boundary layer characterized by
surface dewpoints in the mid to upper 60s, possibly in the 70s
across the James River Valley, beneath steep mid level lapse rates
yields strong MLCAPE values of 2000-3000 j/kg. Deep layer shear
of 30-40kts, locally higher, perpendicular to the cold front/pre-
frontal trough favors discrete supercells in a highly unstable
environment. Thus, all threats with severe convection are
possible as mentioned above. The one limiting factor regarding the
tornado potential is weak low level flow and resulting SRH and
shear. However, given the strength of instability, relatively low
LCLs and likely supercells, a tornado or two is possible. Timing
of initiation is uncertain, as a couple rounds of initiation are
possible with the various forcing features. However, initiation as
early as 18-20 UTC is possible along the pre-frontal trough with
the earlier impulses, with a later round of initiation possible
with the stronger Canadian wave. A special 18Z sounding will be
launched today at Bismarck.

.LONG TERM...(Saturday through Thursday)
Issued at 401 AM CDT Fri Jul 21 2017

Critical fire weather conditions Saturday highlight the extended
forecast. See the fire weather discussion below for details
regarding the possibility for critical conditions southwest and
south central Saturday.

Will continue to monitor the potential for severe convection on
Monday as a cold front is favored by the 00 UTC global suites to
propagate across North Dakota.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 635 AM CDT Fri Jul 21 2017

A cold front will push into western terminals (KISN/KDIK) 12z-15z
Friday, then into the central terminals (KMOT/KBIS) 18z-00z, and
exiting KJMS by 03z Saturday. Threat for showers/thunderstorms will
increase along and ahead of the front, especially during the
afternoon across central ND. Severe Thunderstorms are also expected
with large hail and damaging winds.

With high uncertainty on exactly where/when the precipitation will
erupt today, will continue to mention a VCTS at KMOT/KBIS/KJMS and
await to see how the precipitation evolves. The last of the
precipitation threat ends by 02Z Saturday at KJMS. Morning
thunderstorms are possible at KISN and added a TEMPO group.


Issued at 401 AM CDT Fri Jul 21 2017

Near critical fire weather conditions are possible behind a cold
front this afternoon across southwest North Dakota. Relative
humidity is expected to fall to 15 to 20 percent with high
temperatures in the 90s. The source of uncertainty is forecast
wind behind the front at 15 to 20 mph sustained from the west,
which at this time may fall short of critical levels and occur
during a narrow window. This will closely be monitored.

For Saturday, afternoon humidity between 15 and 25 percent,
northwest winds sustained at 20 to 25 mph with higher gusts, and
temperatures in the 80s are forecast across southwest and south
central North Dakota. When combined with dry fuels, critical fire
weather conditions are possible. A Fire Weather Watch is in


Fire Weather Watch from Saturday afternoon through Saturday
evening for NDZ020-031>035-040>046.



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