Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 172254

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

Issued at 554 PM CDT Sat Jun 17 2017

This update incorporated recent trends in radar imagery and CAMs
through the 21 UTC HRRR into the hourly PoP forecast this evening.
In general, we expect low-topped convection to slowly diminish the
next few hours as low-level cooling reduces MLCAPE that`s been on
the order of 500 J/kg this afternoon. However, the CAM suites are
supportive of isolated to scattered showers continuing in central
ND overnight as a quasi-stationary frontal zone becomes oriented
north-south across that area. Otherwise, we believe the threat of
non-supercell tornadoes has diminished considerably now that the
afternoon convection has dispersed ambient low-level vorticity in
the vicinity of the weak wind shift that extends from near Watford
City to Bismarck and Jamestown as of 22 UTC.


.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 00Z TAFS through 00Z Sunday evening)
Issued at 554 PM CDT Sat Jun 17 2017

Showers and thunderstorms present across western and central ND at
late afternoon will gradually diminish by 06 UTC, but scattered
showers may continue across central ND overnight. Localized and
brief MVFR or IFR conditions remain possible this evening with any
briefly-stronger storms. Otherwise, MVFR stratus will likely form
in central ND tonight and linger into Sunday morning, with a high
probability of occurrence at KMOT and KJMS.




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