Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 210432

Area Forecast Discussion
National Weather Service Bismarck ND
1132 PM CDT Sun Aug 20 2017

Issued at 1132 PM CDT Sun Aug 20 2017

Latest 00Z model suite continues the trend of an increasing 850mb
jet across the west overnight. Large scale ascent increases per
NAM/GFS as a shortwave trough swings southeast from Alberta into
Saskatchewan. Multiple weaker shortwaves were seen across eastern
Montana, and these also shift east overnight. Regional radar indicative
of the above as reflectivities are increasing in western ND, with
a lightning strike observed over Beach in Golden Valley. Current
forecast has scattered showers/thunderstorms evolving from west to
east overnight and this idea remains on track.

UPDATE Issued at 945 PM CDT Sun Aug 20 2017

A few showers continue across south central ND towards the
southern James River Valley. These have been diminishing, and that
trend should continue. Attention then shifts west with the next
wave and an increasing low level jet overnight. The latest NAM and
short term models still agree with increasing rain chances across
western North Dakota, which spread east overnight into Monday.
Have seen some development already in SD, with a few lightning
strikes. The SREF brings the thunder chances a bit farther north
then previous forecast, and have followed that general idea.

UPDATE Issued at 641 PM CDT Sun Aug 20 2017

Late afternoon MRMS Reflectivity at Lowest Altitude product
continues to shows a few showers drifting east across parts of
south central North Dakota towards the James River Valley. The
latest short term high resolution models linger the showers a
little longer than the previous forecast, so have updated to keep
scattered showers around a few more hours. Decided to remove the
thunder mention for early this evening since there has not been
any recent lightning strikes and instability is weak. The next
round of showers will arrive later tonight from the west, and the
forecast has that well covered.


.SHORT TERM...(This evening through Monday)
Issued at 319 PM CDT Sun Aug 20 2017

Cloudy skies and some high-level smoke from fires in Montana are
expected to make the eclipse viewing on Monday a bit iffy. Western
parts of the state appear to have a better shot at mostly sunny
skies by late morning. In Bismarck, the partial eclipse begins at
around 1132 am CDT...with maximum eclipse coverage of 84% occurring
at 1252 pm CDT...and the event ending at 214 pm CDT.

Cool high pressure was centered ovr North Dakota this afternoon with
zonal flow aloft. Scattered light showers over south central North
Dakota - mainly over the southern tier of counties - continued
moving east. These showers were associated with weak upper level
energy impulses in the zonal flow aloft. We expect these showers to
be east of the James Valley by this evening. The latest mesoanalysis
reveals some elevated CAPE - even above the 100mb mixed layer - and
the showers have tapped into this small area of energy and some
lightning strikes were noted in Grant and Emmons counties.

Tonight a shortwave in the upper flow ejects out of the Rockies of
Montana and moves east across ND later tonight through Monday. This
will bring increasing clouds and chances of rain and isolated
thunderstorms to western North Dakota late tonight, then shifting
into central ND during the daytime on Monday. This scenario will
make viewing the eclipse from much of North Dakota challenging with
mostly cloudy skies in the offing. Cant say for sure but looks like
a better chance for clouds than clear skies across the south. Parts
of the west may see some clearing by late morning though. The other
sky element will be high level smoke from fires in Montana. The
latest air quality models indicate light high-level smoke over much
of western and central North Dakota tonight and Monday.

.LONG TERM...(Monday night through Sunday)
Issued at 319 PM CDT Sun Aug 20 2017

The extended forecast begins Monday with scattered showers and
thunderstorms associated with short wave energy currently moving
onshore in the Pacific northwest. This feature will move
southeast into the Northern Plains

Monday night a western upper level ridge builds with the upper level
Canadian low over western Ontario, moving east. This will set up a
northwest flow aloft over North Dakota through at least mid-week.
This scenario will result in a dry but cool forecast for western and
central ND, with highs from the mid 70s to lower 80s. Lows Monday
night from the mid 40s to lower 50s, and lows in the 50s for the
rest of the week.

On Thursday the global models depict the apex of the western ridge
moving east across the Dakotas, as the next low in the upper flow
moves from southern British Columbia and moves east across the
southern Canadian Rockies. This will set up a southwest flow aloft
across the western Dakotas, and chances of showers and thunderstorms
are back in the forecast for late Thursday night through Friday
night with an upper level shortwave in the flow, and associated
surface front moves east across the Dakotas.

Saturday the Canadian low lingers over central Saskatchewan/Manitoba
with weak cyclonic flow over North Dakota, with the system moving
east and setting up a dry northwest flow over ND on Sunday. The
latest consensus models have a dry forecast for Saturday and Sunday,
with high temperatures remaining in the mid 70s to lower 80s.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1132 PM CDT Sun Aug 20 2017

For this TAF period, have a tempo -shra mention at KDIK/KBIS/KMOT
mainly in the 09z-13z timeframe. This might be extended or
adjusted based on current radar trends overnight. Cigs/vsbys still
expected to remain vfr despite the showers. Will watch for
thunderstorms and adjust as needed. A cold front slips through
western and central ND during the day Monday, ending any shower
threat from west to east during the morning and early afternoon.




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