Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 171855

Area Forecast Discussion
National Weather Service Bismarck ND
1255 PM CST Sat Feb 17 2018

Issued at 1254 PM CST Sat Feb 17 2018

No changes for this afternoon. The latest data suggests a slightly
further north migration to the heaviest axis of snow
tonight/tomorrow. Headlines will likely be needed for this event.
We will provide more details soon.

UPDATE Issued at 930 AM CST Sat Feb 17 2018

No major changes required for this update. We will focus on the
approaching storm in detail for the next forecast issuance.

UPDATE Issued at 659 AM CST Sat Feb 17 2018

Little change with this update outside of observed trends through
12 UTC.


.SHORT TERM...(Today through Sunday)
Issued at 322 AM CST Sat Feb 17 2018

An upper level ridge located over the Pacific Northwest will begin
to flatten as a shortwave trough approaches the Northern Plains.
At the surface, a cold front was moving northwest to southeast
across western North Dakota, helping to spark off some light snow
showers across southeastern Montana, western South Dakota, and extreme
southwestern North Dakota. This progressive pattern will promote
the beginning of a cool down, with widespread highs forecast in
the upper teens and lower 20s across the area this afternoon.

Behind the cold front, high pressure will move into the region and
winds will be a bit breezy, mainly across the Missouri and James
River valleys. As we quickly transition to southwest flow aloft,
snow chances will increase from the west late tonight.

For Saturday night into Sunday morning, a quick moving Alberta
Clipper will overspread western and central North Dakota with
light to moderate snow. Moderate to strong frontogenetical forcing
in the lower levels will overlap strong Q-Vector divergence in
the upper levels. Relative humidity greater than 70% in the
dendritic growth zone, coupled with strong upward motion and steep
low level lapse rates all suggest a fairly potent band of snow
will setup somewhere between US Highway 2 and the Interstate 94
corridor. Much uncertainty still exists with regards to placement
of this band as the GFS and Canadian deterministic iterations have
remained consistent regarding a more southerly solution, while
the ECMWF and NAM have remained consistent in advertising a more
northern solution.

The more northern solution seems to make more sense synoptically,
as the dendritic RH looks unrealistic north of the frontogenetical
zone on the GFS as most of its heavier QPF is displaced from the
best frontogenesis/Q-Vector/instability overlap. Still, the 00 UTC
GEFS plumes show fairly tight clustering over KBIS with liquid
QPF values ranging from 0.14 to 0.34 inches. This distribution
resembles the SREF solution as well. Therefore, elected to go with
a blend since there is just too much uncertainty in the forecast
track at the moment. The best bet is still that the area most
favored for at least 3 inches of snowfall accumulation will be in
between I-94 and US Highway 2, and maybe moreso between ND
Highway 200 and US Highway 2 per the northern solutions. With the
banded nature of this event, it is entirely possible that some
locations may see upwards of 5 or 6 inches. Due to the uncertainty
factor, will defer any advisory decisions to the next shift and
will update the SPS as needed.

As the wave departs, breezy winds will cause the potential for
some patchy blowing snow Sunday afternoon, mainly across the
James River Valley, where reduced visibility will be possible in
open country.

Finally, BUFKIT soundings do suggest the potential for some
freezing drizzle to mix with snow at times early Sunday morning
along and south of I-94.

.LONG TERM...(Monday through Friday)
Issued at 322 AM CST Sat Feb 17 2018

On Monday, another shortwave will skirt our southern and
eastern zones, bringing the potential for some more light snow
across these areas. Behind these waves, another shot of arctic air
will bring the potential for dangerous wind chills across western
and central North Dakota through the middle of the week. A slight
warmup is possible by the end of the work week.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1127 AM CST Sat Feb 17 2018

Snow is expected to spread across the state tonight into Sunday
morning. All terminals should experience reduced visibilities and
ceilings in snow and possibly blowing snow. Will carry the
greatest reductions in visibility / ceilings generally after 06Z
with some improvement late in the period, primarily towards KJMS
and KBIS. Light freezing drizzle is possible, especially in
southern North Dakota. The snow is still expected to diminish
Sunday afternoon.




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