Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 311505

Area Forecast Discussion
National Weather Service Bismarck ND
1005 AM CDT WED AUG 31 2016

Issued at 1001 AM CDT Wed Aug 31 2016

Thunderstorms continue to hold on across central north dakota in
an narrow axis of moisture and instability. Have extended the
flood advisory for portions of Logan and Emmons counties as
thunderstorms continue to re-develop in this axis. Mesoscale
models do have this area weakening and shifting slowly east today.
Update mainly for pops and sky cover based on latest satellite and
radar imagery.

UPDATE Issued at 648 AM CDT Wed Aug 31 2016

Focus on this update will be the convection across south central
North Dakota. Current thinking follows the HRRR and diminished the
storms as the low level jet to the west mixes out during the daytime


.SHORT TERM...(Today through Friday night)
Issued at 348 AM CDT Wed Aug 31 2016

Fire weather concerns, windy conditions, and thunderstorm chances
highlight the short term period.

An upper level ridge was well established across the lee of the
Rockies and western Plains states, with an upper level low/trough
off the British Columbia coast. A large surface high was centered
over northern Manitoba with the ridge axis extending south along the
Red River Valley. Meanwhile low pressure continued to develop over
the Rockies. A h925-h850 southeasterly low level jet was already
established, extending over a large area from eastern WY/MT and the
western Dakotas northward into Saskatchewan/Alberta.

Early this morning, the models were depicting developing
thunderstorms over northeastern MT and northwestern ND as upper
level energy moving through the upper level ridge reaches the low
level jet. The showers and thunderstorms would expand and develop
eastward into central ND. Some models were confining the convection
to the north central, while other models hinted at convection
developing along the eastern edge of the low level jet - from Lake
Sakakawea southeast to Bismarck, Napoleon, Ashley area. The
thunderstorms developed east and southeast of Bismarck, likely along
the eastern edge of the low level jet. A good possibility storms
will develop farther north/northeast along the eastern edge of the
LLJ. Any convection is forecast to diminish late this morning.

This afternoon, the upper level ridge axis moves into the western
Dakotas. Surface low pressure continues to develop over the Rockies,
and the pressure gradient tightens across the Plains. Look for
increasing southeasterly winds today. This will allow for increasing
low level moisture to the Dakotas, but the axis of higher dewpoints
shifts eastward into the central Dakota and allows drier air off the
lee of the Rockies to edge eastward into the western Dakotas.
Forecast soundings indicate a good mixing day with adiabatic lapse
rates up to around 5000 feet or around h750. This will allow the
strong low level jet to mix out with the surface layer, and expect
mixing winds to be southeast at 20 to 25 mph over southwestern ND,
and 15 to 20 mph northwest and central ND. Look for highs from the
upper 70s Turtle Mountains and James Valley to near 90 far west. See
fire weather discussion below for details on fire weather issues.

The low level jet increases tonight over ND and reaches far north
into northern Canada. The upper level ridge axis moves east across
ND. This will bring increasing dewpoint temperatures into the state,
with 50s and 60s F values. However, mixing out with the mid levels
is depicted in the forecast soundings should lower afternoon
dewpoints into the 40s and lower 50s. This will also tap into the
low level jet wind speeds. Thus Thursday is setting up to be a very
windy day, with south winds of 25 to 35 mph over western ND and 20
to 25 mph in the central. A wind advisory may be needed for
southwest and parts of south central ND.

The ridge axis moves east of our area beginning Thursday night with
the approach of a large scale upper level low/trough. Thursday night
we should see the beginnings of a series of upper level energy
impulses in the southwest flow aloft reaching ND, bringing small
chances of thunderstorms Thursday night and Friday. The surface
low/trough that develops in the lee of the Rockies ahead of the
upper level trough moves east and approaches western ND on Friday,
bringing warm advection, a continuing very strong southerly low
level jet, and continued low level moisture. Looking at highs Friday
in the 80s to lower 90s.

The surface warm front/trough enters western ND Friday evening, with
the cold front portion of the system catching up to the warm front.
This cold front moves east into central ND Friday night. This will
continue to bring scattered thunderstorms to our area.

.LONG TERM...(Saturday through Tuesday)
Issued at 348 AM CDT Wed Aug 31 2016

The main highlight continues to be increasing chances for
precipitation through the long term period.

The extended period will be impacted by a slow moving h500
trough/ridge system over the central us that will keep a chance for
thunderstorms in place through much of the period.

At the surface the h500 trough will be reflected by a slow moving
surface frontal boundary that becomes aligned with the southwest
flow aloft. This slow moving frontal boundary will be the focus for
thunderstorms across the region Saturday through Wednesday. the
front will also usher in some cooler air with highs falling from the
lower 80s Saturday to the 60s Monday through Wednesday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1001 AM CDT Wed Aug 31 2016

Developing low pressure across eastern Montana will be the focus for
widely scattered thunderstorms between 12z-18z across central North
Dakota as strengthening low level southeast winds bring additional
moisture into the region. Too uncertain to add TSRA to forecast as
the thunderstorms will be widely scattered. Otherwise vfr.


Issued at 348 AM CDT Wed Aug 31 2016

Fire weather concerns are heightened today and Thursday.

Today, minimum humidities drop into the upper teens to
lower 20s across the southwest portion of the state as a band of
higher RH air associated with the morning convection lifts into
central ND, and drier air works into the far southwest. Increasing
pressure gradient will produce sustained winds around 20 to 25 mph
with gusts up to 35 mph over the far southwest. This is where
vegetation has mostly cured and where the greatest fire danger will
exist. The limiting factor will be that these conditions may exist
for 3 hours or so. Confidence is not that great that the RH would
get that low and winds that strong for at least 3 hours. Also
confidence is reduced because yesterday dewpoints were higher than
forecast...and there may be a fine line between high/low dewpoint
values as the low level jet continues to strengthen.

On thursday, we definitely see more moisture advected into
southwest and our lowest afternoon humidities shift farther east
where there is still a significant green component to the
grasses. Another mix-out day, and relative humidity values as low as
25 percent are possible in the northwest, parts of the north
central, and in south central ND. Higher RH is forecast for the
southwest part of the state. However, winds will definitely be
stronger with sustained winds likely 25 to 35 mph and gusts up to 45
mph. Possible wind advisory criteria in addition to possible fire
weather issues. Will continue to monitor.


.BIS Watches/Warnings/Advisories...


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