Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 200551

Area Forecast Discussion
National Weather Service Bismarck ND
1251 AM CDT Tue Mar 20 2018

Issued at 1251 AM CDT Tue Mar 20 2018

Little change was made with this update. Guidance through the 04
UTC RAP and HRRR cycles continues to suggest light snow moving
into western ND after about 09 UTC, a theme supported by upstream
radar trends. We increased PoPs slightly late tonight in western
ND with this update, and may need to adjust them slightly higher
with the next forecast release, but this will be a light event
regardless. Steep mid-level lapse rates may aide some convective
nature to the snow though, which may in turn yield localized but
noteworthy reductions in visibility.

Otherwise, we maintained patchy fog in the forecast area-wide all
the way through Tuesday morning, but based on ASOS/AWOS visibility
trends and model-derived soundings that show some degree of low-
level mixing continuing overnight, we are not very enthused with
fog prospects.

Issued at 958 PM CDT Mon Mar 19 2018

Forecast for tonight remains mainly on track. Main edits were to
hourly weather elements based on latest observations and trends.

Lingering light snow over my southeast, but this will be over by
06Z. Afterwards, still expect increasing chances for light snow
west as an embedded mid level impulse slides into the Northern
Plains. Radar returns already evident via Glasgow MT radar.

Issued at 642 PM CDT Mon Mar 19 2018

Light snow continues to push east across my eastern counties.
Modified POPs based on latest radar and observations, otherwise
other weather elements looked good.


.SHORT TERM...(This evening through Tuesday)
Issued at 222 PM CDT Mon Mar 19 2018

Light snow continues to meander through central into eastern North
Dakota this afternoon and evening. A second wave of snow will
arrive to the west later tonight. Additional accumulations will
be light.

A series of mid-level shortwaves were detected on GOES-East water
vapor imagery eminating from a parent trough moving into northern
Montana. The first wave to the east of the larger scale low was
moving over western ND with a clear mid-level dry slot signaling
the back side of today`s precipitation. Radar analysis showed
bands of light snow still present over areas of the central with
surface observations in Bismarck and Jamestown reporting light
snow at the time of this discussion. This area of snow shifts off
to the east through the afternoon and evening as the mid-level
forcing moves eastward over the state. With the new snowpack and
light winds behind the exiting wave, fog will be possible with
coverage across the west dependent on increasing southerly flow.

The next shortwave is detected over western Montana and progged to
arrive overnight. Steep mid-level lapse rates reaching 8 C/km with
a quick 925-850 mb frontogenesis band over our west/southwest
will add another quarter to half inch of snow to western ND.
Chances for light snow will continue for central North Dakota
through the day Tuesday. Just light accumulations are expected as
the frontogenetical forcing weakens as the shortwave`s focus moves
to our south.

.LONG TERM...(Tuesday night through Monday)
Issued at 222 PM CDT Mon Mar 19 2018

A western ridge begins to build Wednesday night with mid-level
winds turning to the west over ND and associated warm air
advection increasing. With clearing skies in the west expect
temperatures in the 40s Wednesday and Thursday with temperatures
in the 30s.

By Thursday night a potent Pacific trough crosses over the west
coast, marking the beginning of progressive flow aloft over the
Northern Plains. Global models are consistent with increasing mid-
level moisture flow ahead of the wave and the potential for strong
isentropic ascent and a frontogenetical response. Ensemble
guidance remains confident with this being a decent QPF event
given the anomalous precipitable water signal from NAEFS. The
major detail to work out in the coming days is how much QPF will
fall in the form of rain or snow as a thermal gradient will have a
large effect on the amount of snow accumulations possible with
this system.

The 12Z global model suite is consistent with the long wave low
moving across the northern Rockies through the weekend, creating
an active pattern with chances for precipitation from early
Friday through Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1251 AM CDT Tue Mar 20 2018

MVFR and IFR stratus will persist through the 06 UTC TAF cycle for
most of western and central ND. Ceilings will likely lower during
the overnight in many locations, and may only slowly rise Tuesday
afternoon. Light snow will likely impact parts of western ND from
about 09 to 15 UTC, including the KISN and KDIK terminals. Other-
wise, patchy fog is also possible across the area through Tuesday
morning, which could also produce local visibility reductions.




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