Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 172022
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
322 PM CDT Sun Sep 17 2017

.SHORT TERM...(This evening through Monday)
Issued at 321 PM CDT Sun Sep 17 2017

Forecast highlights in the short term period will be a slight chance
of showers tonight in the southwest and James Valley, along with
some patchy frost southwest. Otherwise a warming trend in the offing
for Monday.

Currently, satellite pics indicated the upper low associated with
our recent rains in North Dakota was over central Manitoba. Another
large low was pushing into the west coast of British Columbia,
leaving a zonal upper level flow aloft across the western US.

A weak upper level shortwave in the flow aloft was over southern
Montana/Wyoming this afternoon. This weak wave is forecast to move
east across southern North Dakota and South Dakota. Look for
increasing cloudiness this evening in southern North Dakota, with a
low chance of showers in the south central through the James Valley
tonight.

Weak upper level ridging aloft will occur on Monday over the Dakotas
ahead of the large British Columbia low that begins expanding
eastward into the Canadian and northern US Rockies on Monday. Look
for southerly winds and warm advection, resulting in afternoon highs
from the upper 60s in the Turtle Mountains to the 70s
elsewhere...upper 70s in the far southwest.

.LONG TERM...(Monday night through Sunday)
Issued at 321 PM CDT Sun Sep 17 2017

A large area of low pressure developing into the Pacific Northwest
and eventually the Northern Plains will highlight the long term
period.

Monday night through Tuesday night: An upper level low pressure
system over southern British Columbia Monday evening moves east into
southern Alberta Tuesday. As it does, a significant shortwave in the
base of the low ejects out of Idaho/Wyoming and moves east quickly
across the Dakotas Tuesday and Tuesday night. This will trigger
cyclogenesis in the lee of the Rockies of Montana, Wyoming, and
Saskatchewan, including a strong surface cold front. This cold
front moves east into the western Dakotas/Saskatchewan Tuesday
morning, sweeping east across the Dakotas/Manitoba Tuesday afternoon
and night. We can expect increased southerly winds ahead of the
front and westerly winds behind the front. The increased southerly
winds will also extend well into the mid levels of the atmosphere as
a low level jet that develops up the Plains. This will act to
transport plenty of moisture northward into the Northern Plains.
This scenario will favor good chances of showers and thunderstorms
across much of the Northern Plains. MU CAPE over 2500 J/Kg and 0-6Km
bulk shear of around 50 knts i the James Valley (NAM model) will
provide a favorable environment for strong to severe storms. The GFS
model again is slightly faster than the NAM/ECMWF, but models are
beginning to look a bit closer together regarding movement/timing of
this front. At this time it appears the best chances for severe
storms would be east of Highway 83, favoring the Highway 281
corridor for Tuesday afternoon and perhaps into the early evening
hours.

In addition to the thunderstorm threat, strong winds associated with
the system will be of concern. Bufkit soundings are indicating
strong southerly winds aloft, but a surface inversion with perhaps
some stratus clouds in the near surface layers not allowing mixing
with 40 to 50 knots aloft will make for a mostly cloudy and cool day
with thunderstorms triggered by the front and upper level shortwaves
- mainly in the afternoon - and more likely in the James Valley.
However, forecast soundings are indicating the strong and gusty
westerly winds behind the front will translate to the surface. Thus
expecting a windy day for western and much of central North Dakota
with west winds of 20 to 30 mph with gusts nearing 40 mph at times.

Wednesday: The strong upper low remains over Alberta/Saskatchewan
and becomes more elongated as it deepens into a longwave trough
extending southwestward towards northern California. A strong
southwesterly wind component develops at upper, mid, and low levels.
This would result in gusty southwest winds for much of western and
central North Dakota.

Thursday through Sunday: The upper low/trough continues to deepen
and elongate, becoming a longwave trough extending from Hudson Bay
to its base in southern California by Friday. The trough begins to
make its way across the Rockies through the weekend. This will
result in an unsettled period with off and on chances of showers and
thunderstorms, with fairly seasonable temperatures with highs in the
60s to lower 70s and lows mainly in the 40s to lower 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1218 PM CDT Sun Sep 17 2017

VFR conditions are expected through the forecast period with a light
southerly flow, although beginning more westerly at KJMS through 00
UTC Monday. Band of mid clouds and possible showers will lift from
south central into eastern ND 06-12 UTC Monday. Added a scattered
VFR layer at KBIS and broken VFR ceiling with VCSH at KJMS during
this period. Patchy ground fog possible southwest 10-14 UTC Monday,
but at this time best probability looks to remain south of KDIK.


&&

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

$$

SHORT TERM...JV
LONG TERM...JV
AVIATION...TWH



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