Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 171940
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
240 PM CDT Sat Jun 17 2017

.SHORT TERM...(This evening through Sunday)
Issued at 240 PM CDT Sat Jun 17 2017

Isolated severe thunderstorms possible this afternoon and evening,
favoring the James River Valley; otherwise numerous showers and
scattered thunderstorms continue with atmospheric conditions
favorable for brief funnels and/or landspout tornadoes through
early evening.

After collaborating with Rapid City Forecast Office, will cancel
the wind advisory in the far southwest as winds have not materialized
to advisory criteria thus far. There are indications that advisory
level winds might still be possible in southern Bowman County
this evening, but we can handle it with a special weather
statement if need be.

Currently, large scale ascent sliding from north central ND into the
James River valley, (ahead of a mid/upper level shortwave trough),
will slide atop a stalled frontal boundary which is stretched out
from near Williston to Hazen, and into Jamestown. SPC mesoanalysis
continues to advertise widespread Non-Supercell Tornadic Parameter
values between 1 and 3 north of the frontal boundary. Effective
Bulk Shear has shown weakening trends across the James River
Valley over the last few hours, as the bullseye of 30kt to 40kt
effective bulk shear is now located in southeastern ND. The latest
RAP forecast shows this trend continuing into 00z Sunday, away
from the James River Valley. If this holds true, then would expect
once the convection behind the current boundary arrives late this
afternoon, the mode of convection would mimic pulse like
thunderstorms like we have been observing. The potential for
brief funnels/landspouts remains the main concern given the
strength of the low level instability and surface vorticity, in
combination with weak effective shear mentioned above.

Ascent begins to wane by 06z Sunday, thus after sunset, areal
coverage of convection and intensity should begin to shrink/weaken.
Isolated showers will linger past midnight central ND, with drier
conditions west.

For Sunday, another shortwave trough embedded within northwest flow
and cyclonic curvature will impact the Turtle Mountains south
through the James River Valley with scattered showers and thunderstorms,
mostly during the afternoon and early evening. Not expecting severe
thunderstorms at this time as CAPE values look to range between
500-1000J/Kg/, thus weak instability, along with 0-6km bulk shear
of 20kt, weak shear.

.LONG TERM...(Sunday night through Saturday)
Issued at 240 PM CDT Sat Jun 17 2017

Overall a northwest flow dominates under a persistent upper
low/trough continuing to reside over Ontario, Canada. This is
disrupted briefly at times, especially Tuesday/Wednesday when zonal
flow returns. Thereafter, cyclonic curvature dominates again with
northwest flow and periodic chances for showers and thunderstorms.

For Monday, the far north central and Turtle Mountains will be on
the fringes of some showers and thunderstorms as a shortwave trough
slides through the northwest flow. For Tuesday night, a warm
front/cold front slide through via the westerly flow, still possibly
impacting northern ND and into the northern James River Valley. The
warmest air will arrive with the zonal flow Tuesday/Wednesday with
highs in the lower to mid 80s southwest and south central. Highs in
the 70s return Thursday through Saturday with the northwest flow
aloft along with periodic showers and thunderstorms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 240 PM CDT Sat Jun 17 2017

Showers and thunderstorms will be on the increase this afternoon
across western and central North Dakota.  Coverage is expected to
increase enough to justify the current brief tempo groups in the
forecasts for this afternoon. MVFR/IFR conditions are possible in
any of the thunderstorms. Winds have been a little slow to increase
today, but still think the potential is there for them to increase
this afternoon, especially in the west.   Stratus could linger
tonight in some locations, especially across central and eastern
aerodromes.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...KS
LONG TERM...KS
AVIATION...CK



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