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Area forecast discussion 
National Weather Service Bismarck ND
746 PM CDT Friday Aug 1 2014

issued at 712 PM CDT Friday Aug 1 2014

Updates this evening will focus on thunderstorm chances as a
passing mesoscale convective vortex pairs with afternoon
instability to support an area of thunderstorms over south central
North Dakota. By sunrise...a second mesoscale convective vortex will move through
Williston on its way to the James River Valley by sunset Saturday.
There is a risk for severe storms Saturday afternoon associated
with this second mesoscale convective vortex.


Short term...(this afternoon through Saturday afternoon)

Issued at 333 PM CDT Friday Aug 1 2014

Forecast highlights in the short term period will be thunderstorm
chances through the period.

Currently...surface low pressure centered over far southwest
North Dakota/northwestern South Dakota...with a frontal boundary
stretched from western South Dakota back northwest across eastern
Montana. Northwest flow aloft with middle level shortwave impulses moving
slowly southeast across the region. One of these disturbances is
interacting with the boundary to trigger a few showers/isolated
thunderstorms along to slightly west of the Missouri River this
afternoon. Middle level capping inversion holding convection at Bay
at the moment elsewhere...and also prevented ongoing convection
from strengthening.

Current vorticity maximum across central North Dakota coupled with
increasing MLCAPE along the surface boundary may overcome the middle
level inversion to trigger a few scattered storms late today into
this evening...currently expected across the southwest and south
central near to ahead of the middle level impulse. While widespread
severe weather is not anticipated...enough instability present and
sufficient 0-6km shear for the possibility of a few organized
updrafts and thus a small threat for large hail. Also...ceilings at
around 8-10k feet above ground level or above will elevate the chance for a few
stronger wind gusts with any storms.

Another embedded shortwave spinning over southwestern projected to continue slowly south and east
into northwest/north central ND later this evening and
overnight...sparking additional showers/thunderstorms which look
to continue past daybreak Sat morning over portions of
central/eastern ND. Area of associated surface low pressure will
accompany the middle level wave...with both advertised to linger over
eastern portions of the state middle to late afternoon before exiting
southeast in the evening. Given this forcing and the
instability/shear parameters...a few stronger storms will be
possible across eastern ND during peak heating hours Saturday
afternoon/evening...mainly east of Highway 83.

Long term...(saturday night through friday)

Issued at 333 PM CDT Friday Aug 1 2014

A return to a more active weather pattern will highlight the
extended forecast.

12z models remain in good agreement on an upper level ridge
centered across the intermountain west this weekend...slowly
breaking down with a transition to near zonal flow early next
week. This pattern shift will see daily chances for thunderstorms
associated with impulses propagating along the northern periphery
of the ridge and embedded within the zonal flow. Temperatures will
be near average...highs in the 80s and lows 55-65.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 712 PM CDT Friday Aug 1 2014

Thunderstorms will remain at kbis until 130z. The next round of
thunderstorms will begin at kisn around 05z and will likely hold
together through the day as they move southeast. Areal coverage
and timing are highly uncertain for kmot/kdik/kbis/
thunderstorms are not mentioned at those aerodromes.


Bis watches/warnings/advisories...


short term...New Hampshire
long term...New Hampshire

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