Area Forecast Discussion
Issued by NWS Bismarck, ND

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471
FXUS63 KBIS 110934
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
334 AM CST Sun Dec 11 2016

.SHORT TERM...(Today and tonight)
Issued at 334 AM CST Sun Dec 11 2016

Snow will continue ending from west to east through this morning,
leaving relatively quiet, but continued cold weather in its wake.

As of 09 UTC, a well-defined back edge of moderate intensity snow
is crossing the Highway 83 corridor. Recent RAP and HRRR model
simulations have been well-assimilating current trends and show a
continued eastward progression of the snowfall as the middle- and
upper-level low in northeastern MT continues its movement east. A
very deep dendritic growth zone is present in south central ND per
RAP analysis soundings, with a depth over 11 thousand feet at both
Bismarck and Jamestown. We had an astounding 75 to 1 observed snow
to liquid ratio at Bismarck from 00 to 06 UTC in that environment.
In contrast, observed liquid-equivalent moisture was significantly
less than forecast (relatively-speaking), and that compensated for
the high-end ratios (and likely aided them through lower moisture
content that may have influenced snow crystal structures). That is
leading to snowfall amounts that appear in line with expectations
from the past day. That said, we certainly won`t be surprised if
isolated totals greater than 4 inches are observed in locations
where snow-to-liquid ratios were maximized through the event.

Given good agreement in the consensus of rapid-refresh and high-
resolution guidance, we relied on it to build hourly chances of
precipitation through the day. That generally means that we are
advertising a continued end of snow from west to east early this
morning concurrent with decreasing QG forcing as DCVA diminishes
aloft and mid-level cold air advection begins behind the 850 and
700 mb trough axes. Upstream ASOS trends support some lingering
very light snow or flurries under stratus, but the accumulating
snow will end shortly along the Highway 83 corridor and in the
James River valley between 12 and 15 UTC. We carried some modest
PoPs in the James River valley into the early afternoon though as
the mid-level trough won`t clear that area until 18 to 21 UTC.

A surface high will then quickly move across the area today, and
that will keep temperatures cold with forecast highs mainly near
zero F again. As that high shifts into eastern SD tonight, there
may be an opportunity for enhanced radiational cooling to occur
over parts of south central ND this evening. Thus, depending on
cloud trends, forecast lows may not be cold enough in spots. Yet
another Arctic cold front will be quick on its heels though and
is forecast to enter western ND late tonight. A chance of light
snow will accompany the front between 06 and 12 UTC. Finally, we
need to note that another wind chill advisory may be needed for
parts of northwest and central ND tonight and early Monday with
a later forecast, as well.

.LONG TERM...(Monday through Saturday)
Issued at 334 AM CST Sun Dec 11 2016

Well below-normal temperatures will continue through the week.

The 00 UTC GFS and ECMWF and their ensembles continued to show a
quick-moving, low-amplitude shortwave trough crossing the region
Monday. There`s a quick-hitting, but noteworthy batch of forcing
with this wave per forecast 500-300 mb Q-vector convergence, and
guidance generally agrees in simulating light QPF in the cyclonic
flow accompanying the wave and a low- and mid-level cold frontal
passage early in the day. This could end up being a high PoP/low
QPF scenario with a dusting of snowfall possible in some locales
Monday morning. Behind the cold front a reinforcing shot of cold
air will arrive and deep northwesterly flow will continue through
Wednesday keeping a frigid air mass in place. Guidance suggests a
blustery period will be in store with boundary layer winds around
20 kt making for breezy conditions Monday through Wednesday. Given
the low-density snow pack that`s residing on top of an older, deep
snow field, this will likely be enough to generate patchy blowing
snow and areas of drifting snow in open country. However, analysis
of the Baggaley blowing snow model suggests surface winds need to
be sustained near 30 mph for headline-worthy blowing snow issues.
We`ll continue to monitor for signs of that, but the present set
of model guidance didn`t provide much support for such a scenario.

The global model suites continued to suggest a deeper trough will
likely eject out of the West and into the Plains by late week. We
are carrying a chance of snow in the forecast by Friday since the
00 UTC GFS and ECMWF both supported that possibility, though the
details of that trough`s evolution remain uncertain. It does look
like yet another batch of even colder air could be pulled south-
ward into the region behind that wave, though. The multi-model
consensus and thus our official forecast therefore call for highs
staying well below zero F next Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 334 AM CST Sun Dec 11 2016

A swath of light snow will continue to propagate across western and
central North Dakota through 12z Sunday, then ending from west to
east between 12z and 18z Sunday. With the snow, expect solid mvfr
cigs and ifr vsbys, with temporary ifr cigs at KMOT through 12z
Sunday. After the snow ends, cigs will slowly lift to low vfr by mid
to late afternoon. A cold front will approach KISN/KMOT between 03z
and 06z Monday resulting in a vcsh in their respective terminal
forecasts.

&&

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

$$

SHORT TERM...CJS
LONG TERM...CJS
AVIATION...KS



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