Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 131950

Area Forecast Discussion
National Weather Service Bismarck ND
250 PM CDT Sun Aug 13 2017

.SHORT TERM...(This evening through Monday)
Issued at 250 PM CDT Sun Aug 13 2017

Latest suite of satellite imagery shows a mid/upper level low
circulating over southeast ND, with one last 500mb-300mb vorticity
lobe swinging into the James River Valley this afternoon. With
this vort passage, the mid/upper low will shift east this
evening, as a brief mid level shortwave ridge migrates into
western ND by 12z Monday. Will continue to mention isolated
showers far southern James River Valley through the afternoon.
With mixed layer cape between only between 250 and 500 J/Kg, weak
lapse rates and no shear, feel the threat for thunder will be too
minimal to mention at this time.

For tonight, dry weather will commence as a mid/upper level ridge
transitory ridge shifts from eastern MT into western ND by 12z Monday.
Despite light northerly to northeasterly winds/drier air in the
boundary layer tonight across the southern James River Valley,
enough low level moisture remains per BUFKIT soundings for some
fog formation. This trend continues in the HRRR/RAP13 surface
visibility forecast. Have utilized these models which produce an
area of fog based on expected visibility reductions from 06z-15z
Monday. Future shifts can monitor/adjust as we get closer and fog

Otherwise, the mid level transitory ridge quickly loses its
identity as southwest flow begins to impinge into western ND
Monday morning, with the approach of our next mid level shortwave
trough. NAM/GFS show the strongest synoptic scale ascent shifting
from Alberta into Saskatchewan Monday, with weaker lift extending
into western/central ND. Have collaborated with SPC on the
Marginal Risk for Severe Thunderstorms Monday through Monday night
across southwest ND. A lack of strong forcing, mixed layer/most
unstable CAPE close to zero, along with weak/marginal mid level
lapse rates of 6C to 6.5C/Km, will hinder and limit severe
thunderstorms. This despite decent 0-6km Bulk Shear of 25kt to
40kt. Thus, have gone with the gridded solution which just barely
nudges a mention of thunderstorms in Bowman County Monday
afternoon and evening. This thunderstorm mention is highly
dependent on the SREF model, which also keeps the threat for
thunderstorms/and severe thunderstorms south of our border
Monday/Monday night - per 15Z SREF Calibrated Thunderstorms.

.LONG TERM...(Monday night through Sunday)
Issued at 250 PM CDT Sun Aug 13 2017

Scattered showers expected Monday night with the initial shortwave
mentioned from the short term period. The next shortwave arriving
from the Great Basin will have stronger synoptic scale ascent,
which overspreads western/central ND Tuesday. It also appears to
have a stronger mid level low associated with it, but placement
varies between the NAM/GFS/ECMWF. Overall though, Tuesday represents
a more widespread shower/thunderstorm day then Monday/Monday night.
The SREF 3hr Calibrated Severe Thunderstorm indicates that on
Tuesday, there is some potential for severe thunderstorms in far
south central ND, closest to the ND/SD border. The SPC Day
3/Tuesday Convective Outlook portrays a Marginal Risk for Severe
Thunderstorms mainly in the James River Valley. Showers exit the
James River Valley Wednesday morning, with dry/clearing weather
elsewhere . A quasi zonal flow then ensues through the weekend
with periodic fast moving shortwaves and chances for showers/thunderstorms.
At this time, it appears that Thursday and Friday would support
some chances of showers/thunderstorms while the weekend looks dry.
Given the fast flow and timing of shortwaves, expect changes
throughout the upcoming week.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 250 PM CDT Sun Aug 13 2017

High pressure situated over northern ND into southern Saskatchewan
and Manitoba will move southeast through the forecast period.
MVFR ceilings at KBIS should lift to low VFR around 19Z, with KDIK
and KJMS lifting to VFR around 20Z and 21Z respectively. As the
surface high drifts southeast, a southerly return flow will set up
tonight setting the stage for another round of IFR ceilings and
fog again tonight into Monday morning. For now will hit KJMS
hardest followed by KBIS. Confidence in low ceilings and fog not
as high at KDIK, KISN and KMOT at this time, thus will hold off on
low ceilings and fog for these sites.




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