Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 200654
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1254 AM CST Fri Jan 20 2017

.UPDATE...
Issued at 1245 AM CST Fri Jan 20 2017

Current forecast looks good. Dense fog now in Bismarck with one
quarter mile visibility. Just updated the current conditions.

UPDATE Issued at 941 PM CST Thu Jan 19 2017

Based on satellite trends through 03 UTC and the
HRRR/RAP/GLAMPMELD iterations through 02 UTC, expanded the Dense
Fog Advisory into Burleigh, Morton, Sioux and Wells counties. An
additional expansion is possible later tonight.

UPDATE Issued at 758 PM CST Thu Jan 19 2017

Little change with this forecast update other than to blend to
observed trends through 01 UTC. Fog continues to expand west per
satellite trends, beginning to slowly build into the Bismarck and
Mandan area between 04-06 UTC. Will continue to monitor trends
for a possible expansion of the Dense Fog Advisory later tonight.
Some freezing of fog droplets on roads and sidewalks are possible.

UPDATE Issued at 423 PM CST Thu Jan 19 2017

Based on trends in surface observations/webcams and visibility
forecasts from the rapidly updating suites through 21 UTC, issued
a Dense Fog Advisory through Friday morning for much of the James
River Valley and the far south central, anticipating an expansion
of fog west through the night. The advisory may need to be
expanded even further west later tonight.

&&

.SHORT TERM...(This evening through Friday)
Issued at 248 PM CST Thu Jan 19 2017

The main issue in the short term period is fog and resulting
temperatures.

Weak low pressure remains at the surface with a low level
southerly flow continuing to bring moisture into the northern
plains. Currently, a thin band of stratus/fog is situated over
eastern ND into central and eastern SD, including the southern
James River Valley. This band has been nearly stationary all day.
Latest iterations of the mesoscale models continue to advect this
area east. They`ve been too fast but expect we will see the
stratus/fog spread into central ND tonight. Too little of an areal
extent at this time and too much uncertainty on how quick the low
deck will move west to issue any dense fog headlines, but
certainly see something issued later this evening or on the
overnight shift.

Farther west over central into western ND, it`s been mostly sunny
all day. High clouds will increase tonight, and low stratus will
approach Friday, but we should have a good period of cooling this
evening. Thus we leaned to the cool side of guidance for our
forecast lows for much of central and western ND, with warmer
temperatures in the James River Valley and the far west.

Weak low pressure at the surface and upper levels will remain over
the area Friday. We still have the potential for patchy drizzle or
freezing drizzle, depending on the temperature, mainly over the
James River Valley. Elsewhere, stratus and fog is expected to
spread across the forecast area.

.LONG TERM...(Friday night through Thursday)
Issued at 248 PM CST Thu Jan 19 2017

The main forecast issue in the extended period is the potential
for light accumulations of freezing drizzle through the weekend.

Friday night through Saturday night upper level low pressure lifts
slowly northward through the forecast area, with a weak reflection
remaining at the surface. Forcing will not be strong through the
entire period, but may be enough to create some light qpf, mainly
across eastern portions of central ND through the weekend. This
period, and more specifically late Saturday through Saturday
night, we will see the highest potential for some mixed
precipitation, and some light accumulations of any freezing
precipitation. There are some model differences in cooling and
saturation of the upper levels, thus some significant differences
in resulting ice accumulations. Right now the most threatened area
looks to be around the Turtle Mountains. A GFS solution would
change precipitation over to snow earlier and any ice
accumulation would be light. The NAM indicated that the ice
present aloft will be a lot less, resulting in additional ice
accumulation. We utilize a blend of various models which results
in a mix of light snow and freezing drizzle with meager amounts of
ice accumulation. Will certainly need to monitor the Saturday
afternoon through Saturday night period for possible hazards due
to icing, mainly over eastern portions of central ND. Otherwise,
most areas will remain cloudy through the weekend with area of fog
possible, but most locales over central and western ND will have
much less potential for any accumulating freezing precipitation.
Most areas see the precipitation type change over to snow by
Sunday. Temperatures remain seasonable to slightly above normal
through the weekend.

Next week we see a slow cooling trend. Weak ridging over the area
on Monday breaks down and upper level flow turns northerly with
strong ridging off the west coast, allowing colder air to spill
into the northern plains. A midweek storm tracks across the
central plains late Tuesday through Wednesday. We will still need
to monitor but at this time the track remains mainly across South
Dakota and Nebraska.



&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)

Issued at 1250 AM CST Fri Jan 20 2017

LIFR/VLIFR conditions in freezing fog will continue through much
of the 06Z period at KJMS and KBIS, and will develop Friday into
KMOT. Both KISN and KDIK will trend MVFR-IFR by Friday evening.
Patchy MVFR/IFR fog is possible elsewhere across western North
Dakota this morning. For KJMS & KBIS, some improvement during the
day but conditions deteriorate again Friday night.


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST /11 AM MST/ today for NDZ022-
023-025-034>037-045>048-050-051.

&&

$$

UPDATE...WAA
SHORT TERM...TWH
LONG TERM...TWH
AVIATION...NH


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