Area Forecast Discussion
Issued by NWS Bismarck, ND

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000
FXUS63 KBIS 121249
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
649 AM CST Tue Dec 12 2017

.UPDATE...
Issued at 646 AM CST Tue Dec 12 2017

Made some minor adjustments to sky cover, clearing the west a
little quicker than previously forecast. Otherwise no updates
needed other than populating the latest sensible weather elements
and interpolating to mid-morning values.

&&

.SHORT TERM...(Today and tonight)
Issued at 410 AM CST Tue Dec 12 2017

A mild/tranquil day, then another potent clipper sweeps through
tonight with gusty winds and a wintry mix (mainly east central ND).

Early this morning, the latest fog/stratus satellite imagery loop
and surface analysis/observations continue to show a stratus deck
moving from north to south, and at the same time propagating
eastward, ahead of a low level warm front. Stratus is currently
bounded along and east of a line from Rolla to Rugby, and from
Harvey to Selfridge. Expect this area to exit the Turtle Mountains
and James River Valley 12z-15z today. Upstream into central and southern
Canada, scattered mid/high clouds will be directed south today via
a northerly flow aloft. Western and central ND will remain in the
warm sector today, thus expect another nice afternoon with plenty
of sunshine. Highs will mostly be in the 40s, with low and mid
50s in the southwest.

The tranquility will not last. Latest water vapor imagery indicative
of our next shortwave and associated surface cold front/clipper.
A compact/potent mid to upper low was vividly seen over central
British Columbia this morning, moving atop a persistent/highly
amplified upper level ridge which stretched from Nevada through
the northern Rockies. This upper low is similar to the one that
moved through 24hours ago, and will expect similar weather conditions
as Monday night. The shortwave will will arrive in northwest ND
near midnight tonight, and exit south central ND by 12z/6AM CST
Wednesday. In doing so, a quick but intense area of synoptic
scale ascent will push from northwest to southeast between
midnight and 6AM. A surface cold front will also shift from north
to south, as west to northwest boundary layer winds increase to
between 25kt to 35kt. BUFKIT soundings show top layer mixed winds
to around 40kt. Expect increasing winds overnight through
Wednesday morning, then diminishing in the afternoon. The 3 hourly
pressure rises are not as strong as Monday nights system, but
nonetheless, a strong west to east pressure gradient, and
strong/unidirectional winds within a well mixed layer will
transfer down to the surface resulting in windy conditions. Most
likely the sustained winds/gusts will fall within wind advisory
criteria, but will let the dayshift and possibly the evening shift
re-evaluate the timing and strength of the winds with the latest
upstream observations and guidance. In terms of precipitation with
this system, after collaborating with our neighboring offices, we
sided with the wetter ECMWF and GFS for precipitation. Soundings
show a wintry mix developing from the Turtle Mountains south into
the James River Valley tonight, extending west to near Bismarck.
Like we saw Monday night, with a well mixed boundary layer,
surface temperatures will remain above freezing except in the
Turtle Mountains and in the far northern James River Valley
through 6AM Wednesday. Light freezing rain and/or snow is the most
likely weather scenario, given we gradually lose ice production
aloft followed by weak omega/vertical motion within a low level
saturated/supercooled layer. Along with the Grand Forks Weather
Forecast Office, we will be issuing a Special Weather Statement
highlighting the wintry mix potential and strong winds.

.LONG TERM...(Wednesday through Monday)
Issued at 410 AM CST Tue Dec 12 2017

The long term remains active with successive clippers resulting in
periods of gusty winds and continued chances for precipitation.

As mixing heights increase by mid Wednesday morning, the saturation
level looks to get back into the -10C to -12C ice crystal growth
zone, resulting in a light snow/light freezing rain mix across
east central ND. Elsewhere it will be windy but dry. This will be
short lived too, as another shortwave and clipper in the northwest
flow aloft sweep through Wednesday night/Thursday. Winds not as
strong, and precipitation looks to be mainly in the form of light
snow. Central ND could see a dusting to a half inch through Thursday
morning. Another break in the weather Thursday night into Friday
morning, followed by the next clipper Friday afternoon into
Saturday morning, and another late Sunday into Monday.

Beyond this long term period, the weather pattern is still trending
much colder towards the end of next week. More on this in future
discussions.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 646 AM CST Tue Dec 12 2017

Mvfr cigs now exiting KJMS. Elsewhere, vfr cigs will continue
this Taf period. A cold front will push from northwest to
southeast after 00z Wednesday. Increasing west to northwest winds
to between 25kt and 35kt will evolve 00z-06z Wednesday. Prior to
the strong winds at the surface, there will be a brief period of
low level wind shear at KDIK/KBIS/KJMS.

&&

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

$$

UPDATE...TWH
SHORT TERM...KS
LONG TERM...KS
AVIATION...TWH



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