Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 181205

Area Forecast Discussion
National Weather Service Bismarck ND
605 AM CST Sat Feb 18 2017

Issued at 605 AM CST Sat Feb 18 2017

Latest Bowman and other regional radars show a trend towards
increasing reflectivitys over a greater areal coverage across
southeast Montana, far southwest North Dakota, and western South
Dakota. The latest 06z guidance per NAM/GFS, as well as the
higher resolution NAMNest and NMM east have initialized well with
current radar trends. Thus, have followed the above models to
update/increase POPS and areal coverage today, following the
synoptic scale ascent and frontogenetical forcing as it shifts
from southwest to northeast through the day.


.SHORT TERM...(Today and tonight)
Issued at 325 AM CST Sat Feb 18 2017

The latest water vapor imagery shows a return towards a longwave
upper trough along the west coast which will continuously reload,
as several shortwave troughs eject out into the central and
northern high plains in the days ahead. That said, with a west
coast trough, a predominate west to southwest flow aloft will mark
the transition toward a more active weather pattern in western and
central North Dakota resulting in a potpourri of wintry/springlike
weather at times, as there is a potential for thunderstorms south
central and southeast Monday.

For today, a couple of shortwaves scooting northeast from southeast
Montana is already producing mid/high level clouds into southwest
North Dakota. Bowman radar showing some weak reflectivity`s within
the clouds. The NAM/GFS indicate enough synoptic scale ascent aligning
with weak 850mb-700mb frontogenesis to generate a mention of low
pops/slight chances of rain showers west into portions of south
central today. This idea also has support from the simulated composite
reflectivity`s per NAMNest, ARW-East, and NMM East high
resolution models. Otherwise expect a mostly cloudy day with highs
in the upper 30s north to upper 40s southwest.

Warm air advection ensues tonight with south to southeasterly low
level flow. With increasing vertical motion and moisture advection,
expect more clouds forming tonight, most likely much lower in
height/stratus clouds becoming dominant per BUFKIT soundings.
Overnight lows will be in the upper 20s to lower 30s.

.LONG TERM...(Sunday through Friday)
Issued at 325 AM CST Sat Feb 18 2017

As mentioned in the short term discussion, an active long term
period lies ahead. With multiple shortwaves embedded within a
southwest flow Sunday, synoptic scale forcing is maximized in the
north central with a chance for light freezing rain Sunday morning,
then warming to above freezing temperatures for a chance of rain
in the afternoon. Clouds will hold during the day across the north
resulting in highs in the upper 30s, while farther south, it should
become partly sunny with highs in the mid 40s south central and
lower 50s southwest.

For Sunday night and Monday, a well defined shortwave trough
currently in southern California ejects into central North/South
Dakota Monday morning. With strong synoptic scale ascent aligned
with lower level frontogenetical forcing, and mid level lapse
rates around 6.5C/km resulting in conditionally unstable
environment, expect likely pops with a wintry mix west and north
in the morning, with rain showers likely elsewhere. A chance of
thunderstorms in the southern James River Valley is also possible
with this potent shortwave trough. SPC Day 3 has south central ND
and the James River Valley in a General Thunderstorm Outlook.
Given the GFS 0-6km bulk shear of 50kt in the southern James River
Valley along with 250 J/kg most unstable 0-1km cape, will follow
SPC and add in a slight chance mention of thunderstorms in the
southern James River Valley Monday. Will re-evaluate future model
runs as to whether or not to expand this area into south central
ND in later forecasts.

Although timing differences emerge between the faster GFS and
slower ECMWF, both indicate another shortwave ripping through
Tuesday through Wednesday. This will mainly effect northern North
Dakota based on the low pressure tracking north of Interstate 94
on both models.

As was been mentioned in previous discussions, there is another
impressive shortwave for Thursday and Friday, but trends continue
to favor a southerly track. This would mainly affect southern
North Dakota into South Dakota, essentially along and south of
Interstate 94. However despite the recent trends of a more southern
track, a lot of uncertainty remains this far out. Behind this
system, the weather pattern appears colder and continued active on
both the GFS and ECMWF.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 605 AM CST Sat Feb 18 2017

Mid level clouds will overspread the terminals today (approximately
10kft AGL). Winds will remain light and become east to southeast
this afternoon through tonight. Low level moisture will increase
Saturday night, with low clouds/mvfr cigs developing late tonight at
KDIK/KBIS,between 10z-12z Sunday. Ifr to lifr cigs are anticipated
at KISN/KMOT respectively, between 04z-12z Sunday.




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