Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 121123
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
623 AM CDT Wed Aug 12 2020

.UPDATE...
Issued at 622 AM CDT Wed Aug 12 2020

Rain is ending southeast. No major changes made for this update.

&&

.SHORT TERM...(Today and tonight)
Issued at 327 AM CDT Wed Aug 12 2020

Today will be hot, humid and stormy.

Low level southeast winds around 20 mph ahead of a sharpening
surface trough over eastern Montana will advect 60s-70s surface
dewpoints into western and central North Dakota. Highs are
forecast to reach the upper 80s east to upper 90s west. This will
result in heat indices in the low to upper 90s.

Convective initiation appears likely along the surface trough as
it approaches the ND/MT border late this afternoon or early
evening, but there is still uncertainty in the location and
coverage of storms. The best chance for storms appears to be
across the northwest and into southern Canada where mid level
height falls are greater, CIN is weaker and upper-level forcing is
stronger. It also appears that deep layer shear will also be
greater farther north, with an average around 40 knots vs 30 knots
across the south. With ML CAPE of 2000-3000 J/kg and 30-40 knots
of shear, organized severe storms are possible. Initially,
discrete supercells would appear to be the favored storm mode
given shear vectors should be orthogonal to the surface trough.
Even though supercells are anticipated, the tornado risk appears
very low due to higher LCLs and marginal at best low level SRH.

There are indications in the CAMs that convection could grow
upscale into an MCS and spread into central North Dakota
overnight. If this occurs then the main threat will transition
from large hail to enhanced damaging winds.

.LONG TERM...(Thursday through Tuesday)
Issued at 327 AM CDT Wed Aug 12 2020

Chances for thunderstorms continue through Friday, with mainly dry
and cool weather expected for the weekend into next week.

The larger, synoptic-scale trough will eject across the Northern
Rockies on Thursday, with a downstream surface trough refocusing
from northeast to south central North Dakota by Thursday
afternoon. Thunderstorms may redevelop along the surface trough
late Thursday afternoon or evening, but the potential for
convection earlier in the day adds uncertainty. Strong
instability and mid-level lapse rates and increasing shear would
support a severe threat with any storm that develops. Heavy rain
will also be threat given moisture transport vectors orthogonal
to the boundary and storm motion vectors and high PWATs. It will
remain warm and humid across south central and southeast North
Dakota on Thursday, with cooler temperatures farther north and
drier conditions in the west.

The upper level trough axis is forecast to shift over the Northern
Plains on Friday. The cyclonic flow regime may produce some
afternoon showers or thunderstorms in a low CAPE/high shear
environment. Beyond Friday, models tend to favor a transition to
northwest flow aloft and surface high pressure through early next
week, resulting in mostly dry weather and below normal
temperatures.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 622 AM CDT Wed Aug 12 2020

VFR at all TAF sites through the TAF period. Breezy southerly
winds will develop today. Thunderstorms are expected across
western ND late this afternoon and should push eastward through
the evening hours. KXWA and KMOT are most likely to see
thunderstorm activity and the threat is mentioned in the TAFs for
those locations. Confidence decreases further south.


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...AJ
SHORT TERM...AJ
LONG TERM...AJ
AVIATION...AJ


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