Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 151157

Area Forecast Discussion
National Weather Service Bismarck ND
657 AM CDT Fri Sep 15 2017

Issued at 657 AM CDT Fri Sep 15 2017

Latest radar imagery shows showers continuing to push into western
and central ND. Well defined upper low centered over southern
Wyoming shows up nicely in GOES-16 mid-level water vapor imagery,
slowly advancing northeastward. Have a few reports of around 0.25
inches of precipitation over far western ND already. Forecast is
on track, so no changes were made.


.SHORT TERM...(Today and tonight)
Issued at 322 AM CDT Fri Sep 15 2017

Widespread rainshowers, gusty northeasterly winds, chilly temperatures,
along with embedded isolated to scattered thunderstorms southwest
and south central today.

The latest water vapor imagery shows two distinct/strong shortwaves.
The first was over eastern Utah, and the second over southeastern
Oregon/southwestern Idaho. Multiple leading/weaker shortwaves
were out ahead of these more significant ones mentioned above. Local
and regional radar shows scattered showers in western and central
ND, with a large swath of rainshowers in eastern Montana and
northwestern South Dakota, all moving to the northeast.

For today/tonight, it will be the shortwave trough in eastern Utah
rotating up and moving into southwestern North Dakota this afternoon,
then moving into the Turtle Mountains tonight. Synoptic scale ascent
associated with this shortwave trough is strong, and will overlap
with strong 850mb-700mb frontogensis for roughly a 6 to 12 hour
period as the maximum area of lift/vertical motion shifts from
western into north central ND today/tonight. This is where
precipitation amounts will be highest with rainfall forecast
amounts between 1 and 2 inches through tonight. Between 0.50
inches and 1 inch of rainfall is expected for most of south
central ND through tonight, with around a third of an inch in the
southern James River Valley. A closed 700mb low moves into
southwest ND this afternoon with a strong vertical motion field
per GFS/NAM BUFKIT sounding profiles. Elevated thunderstorm
potential that was mentioned in yesterday`s discussion highlighting
strong to marginally severe remains on track. The high resolution
models/simulated composite reflectivities certainly show a trend
of embedded thunderstorms southwest and south central beginning
mid to late morning and continuing through the afternoon. Environment
will be characterized by low cape/high shear. Elevated Cape of
500 J/kg to 750 J/kg above 700mb along with high effective shear
of 35kt to 40kt. Some of these thunderstorms may produce small
hail. The SREF 3hr calibrated severe thunderstorm forecasts keeps
the higher probabilities in the far southern James River Valley
today. Per SPC outlook, General thunderstorms can be expected
across southwest and south central today. Gusty northeasterly
winds today of 15 to 30 mph will result in apparent temperatures
in the mid to upper 30s for portions of the west, keeping in mind
that actual highs will be in the upper 40s. Quite a difference
from the mid 90s from a few days ago. Overall, a raw day
temperature-wise with upper 40s west, to lower 50s central, to
some lower 60s in the southern James River Valley.

The rain continues tonight, but does begin to taper off in the
south central and southeast after midnight, as the strongest
forcing shifts into the north central and Turtle Mountains.

.LONG TERM...(Saturday through Thursday)
Issued at 322 AM CDT Fri Sep 15 2017

A longwave trough continues in the west through the long term
period resulting in an unsettled weather pattern. Frost late
Saturday night into Sunday morning across the west still remains
on track.

The second shortwave trough mentioned from the short term period
swings through Saturday, focusing most of the rain showers in the
west and north central. The south central has more of a dry slot
pushing through, limiting precipitation. With plenty of clouds and
northerly winds, highs will once again range from the upper 40s
west to lower and mid 50s elsewhere. As this shortwave departs
Saturday night, a clearing sky in the west along with light winds
will give way to overnight lows Saturday night/Sunday morning in
the mid 30s. Thus, frost looks increasingly likely.

Sunday will be dry as a transitory ridge slides through. Afternoon
highs will rebound into the lower 60s. A weak shortwave migrates
through Sunday night, mostly affecting south central ND and the
James River Valley with a chance of showers. After a break in the
shortwaves/precipitation Monday, another shortwave pushes through
Tuesday/Tuesday night. Instability parameters on the GFS shows
some potential for strong to possibly severe thunderstorms south
central and into the James River Valley Tuesday afternoon/evening.
Will continue to monitor the timing of this shortwave and an
associated cold front. The next in a series of waves and
precipitation affects western and central ND Wednesday night
through Friday. Highs will mostly be in the 60s and 70s.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 657 AM CDT Fri Sep 15 2017

Showers continue to spread across ND as a fall storm system
approaches the region. All locations are already IFR due to low
cigs with exception of KMOT and KBIS. Expect mainly IFR conditions
at all locations through tonight. Breezy northeasterly winds are
also expected. Some elevated instability is in place so have
included VCTS for KBIS and KJMS this afternoon and early evening.




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