Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 260300

Area Forecast Discussion
National Weather Service Bismarck ND
1000 PM CDT Tue Apr 25 2017

Issued at 939 PM CDT Tue Apr 25 2017

Latest guidance has been shifting tonight`s mesoscale banding
setup further west...placing a stronger zone of ascent focused
over the southeast corner of the CWA. This area could see up to
2-4 inches of snowfall with a possibility of higher localized
amounts under stronger mesoscale banding...especially in Dickey
and LaMoure counties. Otherwise, blended temperatures with the
latest observations.

UPDATE Issued at 639 PM CDT Tue Apr 25 2017

Current forecast looks in good shape. Populated latest sensible
weather elements and interpolated to mid evening values. Did lower
sky cover a bit early this evening far north, but expect mid and
high level clouds to increase there through the evening. As far as
the potential mesoscale banding tonight into Wednesday, latest
iterations of the HRRR/RAP continue to focus mainly on Dickey and
Lamoure counties in the southern James River Valley. Currently
not much going on over southern North Dakota. A band of light snow
is developing over northeast South Dakota. Will see how this
develops over the next several hours as upper low is forecast to
propagate from western SD this evening, into north central SD
around midnight, and then move slowly into northeast SD through
through midday Wednesday.


.SHORT TERM...(This evening through Wednesday)
Issued at 328 PM CDT Tue Apr 25 2017

Weather concern is for a potential mesoscale banding of snow
setting up across the far southern James River Valley late tonight
through Wednesday. Per Oakes NAM/RAP13 Oakes BUFKIT sounding, even
without mesoscale banding, there is enough large scale ascent/omega
occurring within the dendritic growth zone (-12c to -20C) along
with steep mid level (700mb-600mb) lapse rates to produce
snowfall amounts of between 2 and 4 inches tonight through
Wednesday afternoon. This covers central/eastern LaMoure and
Dickey counties, with some potential to extend a bit farther west
into Logan and McIntosh counties per RAP13.

Collaborated with WPC and surrounding offices, and the overall
assessment is that the NAM12 holds merit with regards to large
scale forcing/ascent, but mesoscale processes associated with the
high qpf/snowfall has enough uncertainty at this time to question
its validity. Thus confidence is low at this time for heavy
snowfall. The banding of snow, if it does setup, would not do so
until 3 to 6hr prior to the event, so a close monitoring with
later tonight into Wednesday for any indications of mesoscale
banding is the best course of action at this time.

Confidence is higher with the 2 to 4 inch range in the southern
James River Valley, as the experimental HRRR/GFS20/ECMWF/SREF are
more in line with WPC snowfall amounts.

Latest suite of satellite imagery shows a mid/upper level closed
low circulating over eastern Wyoming. This is forecast to slide
and transfer east into western and central Minnesota Wednesday.
With the 500mb low lingering over the far southern James River
Valley Wednesday along with a 60kt jet streak, precipitation is
expected to continue for most of the day Wednesday before tapering
off in the evening. The 12Z NAM12 holds this jet through most of
the day, while the GFS shifts it east after 12z Wednesday.

Rest of forecast area is dry and cold with sky conditions improving
from mostly cloudy to mostly sunny, from west to east in the
afternoon. Highs will range from the upper 30s Turtle Mountains
south into the James River Valley to the 40s elsewhere.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 328 PM CDT Tue Apr 25 2017

Overall a dry and cool pattern continues initially (through
Friday), with temperatures moderating into the 50s Saturday
through Tuesday. The storm track remains with the southern jet
stream which remains south of North Dakota. Other than a weak
frontal passage Saturday with a chance of pops northwest, expect a
fairly tranquil pattern through Sunday. Monday and Tuesday the
pattern looks to become active again as the northern stream eventually
pushes a cold front through by the end of the extended period.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 939 PM CDT Tue Apr 25 2017

Mainly MVFR ceilings at KDIK, KBIS and KJMS through tonight and
Wednesday morning. Periods of IFR ceilings are possible,
especially at KJMS around 09-13 UTC when snow approaches the site.
For now went with a VCSH and a tempo -SN with 5SM VSBY and BKN 800
ft ceiling during that period. Ceilings improve to VFR at KDIK
and KBIS Wednesday afternoon. At KISN and KMOT mainly VFR
conditions, with a period of MVFR ceilings possible Wednesday
morning, especially at KMOT. North to northeast flow will
continue at all TAF sites through the forecast period.




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