Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 230633 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Bismarck ND
133 AM CDT Fri Mar 23 2018

Issued at 116 AM CDT Fri Mar 23 2018

As of 625 UTC, precipitation was observed on the ND ARB Bowman
radar spreading into far southwest North Dakota. RAP soundings and
observed surface temperatures favor mostly snow with
precipitation onset in the Dickinson area, with a possible mix
further southwest. With strong winds and temperatures near
freezing, snowfall is likely to compact. That said, the trends in
the RAP/HRRR through their 03 UTC iterations, the 00 UTC Hi-Res
Window NMM and ARW, and the 00 UTC GFS favor greater snowfall
potential given slightly cooler temperatures that are being
observed thus far, especially across southwest and south central
North Dakota. Thus, did increase snowfall amounts by a couple
inches from the previous forecast for these areas. The band of
heavy snow is expected to arrive in Dickinson around 08 UTC,
Williston around 10 UTC, Bismarck around 12 UTC, Minot around 14
UTC and Jamestown around 15-16 UTC based on the RAP/HRRR.

GOES-East Mesoscale Sector Number 1 is in place over the Northern
Plains for this storm.

UPDATE Issued at 956 PM CDT Thu Mar 22 2018

Just some minor updates to pops to account for a slightly slower
arrival of precipitation to the southwest late this evening. A
look at the latest mesoscale guidance for pops during the morning
Friday shows a pattern very similar to the previous forecast. With
a later arrival, this cut back QPF slightly before midnight.
Overall, no significant changes to the current snowfall forecast.
Updated text products will be sent shortly.

UPDATE Issued at 640 PM CDT Thu Mar 22 2018

No significant updates early this evening other than populating
latest sensible weather elements and blending to mid-evening
values. Areas of fog have mostly dissipated this afternoon, but
some patchy areas of fog remain and expect areas of fog and
stratus overnight ahead of the approaching storm system. No
changes to current hazards. Updated text products will be sent


.SHORT TERM...(This evening through Friday night)
Issued at 238 PM CDT Thu Mar 22 2018

Main highlight is the winter storm set to arrive early Friday
morning. All types of wintry precipitation will be possible with
heavy snow likely for northwest, central, and eastern North

Water vapor analysis depicts a potent Pacific trough with southwest
flow over the Great Basin and into the northern Rockies. The
downstream upper level ridge axis was centered over the eastern
Rockies into eastern Montana and through the western Canadian
prairies. Light winds and subsidence associated with the
anticyclonic flow aloft was keeping fog in place through areas of
western and central North Dakota. Would expect at least areas of fog
to continue tonight as the upper ridge axis shifts over the state.

Overnight tonight a shortwave ejects out of the western trough and
on over the northern Rockies. Mid level winds turn southeasterly,
with winds at 850 mb increasing to 40-50 knots by early Friday
morning and enhancing moisture transport ahead of this wave. A band
of deep frontogenesis overlaid by Q-Vector convergence crosses into
southwest ND during the overnight hours, signifying the arrival of
strong mesoscale-synoptic coupled ascent. This band pushes eastward
through the day. Expect mostly rain in the far southwest where a
warm nose aloft remains strongest and a transition to snow over west-
central ND. Greatest confidence for heavy accumulating snow lies in
a swath of 8 to 12 inches from northwest and north-central ND down
southeast through the upper James River Valley.

The major note of concern in this forecast remains precipitation
type along a thermal gradient mostly aligned with the Missouri River
through Lake Sakakawea. Forecast soundings in this area depict a
temperature profile near freezing for much of the event which will
A) create lower snow ratios and B) potentially create an area of
more liquid precipitation which would drastically cut down snow
accumulation totals on the southwest edge of the band of snow.

A second area of concern in snowfall totals is an area of drier air
in the 12Z NAM/GFS runs progged to pass over south-central North
Dakota by mid-day Friday. The impact on snow accumulations will
depend on the depth of this dry layer, but could be a reason for a
lull in precipitation across the south-central during the day

Tightened surface pressure gradients associated with the deepening
low will be responsible for wind speeds up to 20-30 kts. While
this means blowing snow and lowered visibilities will be a threat
with this storm, the nature of the wetter snow will mean the
blowing snow threat will be less than what would normally be
expected with this wind/snowfall combination.

As this wave meanders off to the east, a loss of ice growth aloft
will lead to a threat of freezing drizzle on the back end Friday night.

.LONG TERM...(Saturday through Thursday) Issued at 238 PM CDT Thu
Mar 22 2018

The aforementioned Pacific trough crosses the western coastline
overnight Friday night into Saturday, continuing southwest flow
over the Northern Plains. Another wave ejects over the northern
Rockies early Sunday morning, bringing chances for mixed
precipitation through the day. Models diverge in agreement on
synoptic forcing and moisture associated with this system, which
leaves high uncertainty for totals and precipitation types.

Into next week, global models hint at a deep low moving through
the southwest with a northern Canadian low to our north. There are
signs of a few impulses moving through the cyclonic flow over our
area but once again certainty in any timing or intensity remains


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 116 AM CDT Fri Mar 23 2018

Widespread LIFR/VLIFR conditions in heavy snow developing through
the night across southwest North Dakota, spreading into northwest
and central North Dakota Friday morning. The band of heavy snow
is expected to arrive at KDIK around 08 UTC, KISN around 10 UTC,
KBIS around 12 UTC, KMOT around 14 UTC, and KJMS around 15-16
UTC. Fog is likely to precede precipitation for most areas. Strong
southeast winds with gusts of 30-40 kts are expected to accompany
the snow. Snow may change over to rain across southwest North
Dakota Friday afternoon. Precipitation will decrease from west to
east Friday evening. Patchy freezing drizzle is possible Friday
night into Saturday morning.


Winter Storm Warning until 7 AM CDT /6 AM MDT/ Saturday for

Winter Weather Advisory until 1 AM CDT /midnight MDT/ Saturday
for NDZ017-032-033-041-042-045-046.

Winter Storm Warning from 7 AM this morning to 7 AM CDT Saturday
for NDZ001>005-011>013-022-023-025-036-037-047-048-050-051.



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