Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 110648
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1248 AM CST Sun Dec 11 2016

.UPDATE...
Issued at 1248 AM CST Sun Dec 11 2016

The going forecast remains on track and all we did was again blend
observational trends into the gridded forecast, which mainly meant
we increased PoPs in the 07-10 UTC time range into the 100 percent
range over more of the area. We also lingered higher-order PoPs in
northwest and north central ND a bit longer than before as RAP and
HRRR simulations suggest weak mid-level frontogenesis should cause
light snow to linger longest in that area. That guidance and the
00 UTC WRF-ARW and NMM simulations all suggest the axis with the
greatest snowfall totals near 4 inches will be from Minot toward
Harvey and Carrington by morning. Interestingly, the observed snow
to liquid ratio here in Bismarck at 06 UTC was an astounding 75 to
1, which is supported by RAP analysis soundings that show a high-
end dendritic growth zone which is about 11 thousand feet deep. In
contrast, observed liquid-equivalent moisture was only 0.02", much
less than forecast (relatively-speaking), so we believe there`s a
compensation going on that allowed us to stay the course with the
going forecast idea. That said, we won`t be surprised if isolated
totals greater than 4 inches are observed somewhere where snow to
liquid ratios remain maximized through the event.

UPDATE Issued at 924 PM CST Sat Dec 10 2016

Snow continues to spread over the area with the approach of the
aforementioned wave. Previous forecast appears in rather good
shape, and will only do some modest precipitation chance
adjustments based on current obs/radar.

UPDATE Issued at 611 PM CST Sat Dec 10 2016

Main changes for early evening update were to push up snow chances
through tonight into Sunday morning. Rather broad area of snow,
sometimes on the heavier side, has developed over eastern Montana with
the approaching wave. Have increased snow amounts a bit over the
northwest, but anticipated amounts remain below advisory criteria.
Models show that snow will probably linger into the morning over
eastern locations.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 334 PM CST Sat Dec 10 2016

The focus of the short term forecast is the expected snow continuing
this afternoon through tonight and Sunday morning. 1 to 4 inches of
snow is expected across western and central ND...with most areas
receiving 2 to 3 inches of snow.

This afternoon...good area of isentropic lift continued across
mainly western and south central ND. Strong southerly flow at h850
and westerly flow at h700...with the 285K surface showing isentropic
lift. The h700-h500 frontogenesis indicated increasing frontogenesis
from noon to 6 pm today from northwest ND to south central ND...which
shifts eastward later this evening. This is the first area of light
snowfall accumulations...which may bring 1 to 2 inches of snowfall
to some areas in the northwest and south central areas by early this
evening.

Tonight and Sunday...an upper level shortwave over central MT today
moves east across ND tonight and Sunday, bringing a period of strong
h77-500 Q vector convergence. Model consensus depicts 1 to 3 inch
snowfall totals with this feature. The snow should taper off from
west to east during the early morning hours in western ND and later
Sunday morning in the James Valley.

It is possible that some lake effect snow from Lake Sakakawea may
enhance the snowfall totals. Surface winds were easterly, with winds
just off the surface becoming southerly...thus more enhanced
snowfall may occur on the western and northern edges of the lake.

.LONG TERM...(Sunday night through Saturday)
Issued at 334 PM CST Sat Dec 10 2016

Frigid temperatures are here to stay through the long term thanks
to reinforcing surges of Arctic air Monday and Tuesday night.

The models remain in good agreement in large scale
features...keeping a deep h500 low over central Canada and cold
northwesterly flow over ND through much of next week. An arctic
front Monday...with another Tuesday night should be accompanied by
some post-frontal gusty northwest winds. A shot of light snow from
Monday`s system should bring little to no new snow accumulations.

Late in the week the deep Canadian low moves east with a more
progressive pattern resulting. A trough develops over the west coast
and Rockies as another shot of arctic air arrives. The models are
developing a surface low storm system over the central Rockies and
the storm system emerges into the Central Plains. This could bring
more snow to our area...with ND on the northern fringe of the
precipitation. Whether this occurs - or whether the reinforced
arctic air keeps the precipitation shield farther south and east of
our area - is one of the big questions with this system. For now,
the model consensus results in a chance of light snow to southern
ND. We will need to keep an eye on the model run to run consistency
with this storm system.

High temperatures mainly ranging from 5 above to 5 below zero...with
lows below zero each night through the long term.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1248 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.
&&

$$

UPDATE...CJS
SHORT TERM...JV
LONG TERM...JV
AVIATION...KS


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