Area Forecast Discussion
Issued by NWS Bismarck, ND

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023
FXUS63 KBIS 302338
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
638 PM CDT TUE AUG 30 2016

.UPDATE...
Issued at 634 PM CDT Tue Aug 30 2016

A few light showers continue to show up on radar over portions of
western North Dakota, though these have been diminishing over the
past hour or so. Models continue to show greater chances for
showers and thunderstorms developing overnight as low level jet
increases, with chances sliding easterly early Wednesday morning.
Going forecast continues to reflect this well. Only change for
early evening update was to increase cloud cover a bit over the
west with the ongoing light showers and clouds remaining from
previous activity.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 251 PM CDT Tue Aug 30 2016

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

Upper level ridging continues across eastern Montana and the
western Dakotas this Tuesday afternoon. A weak wave is producing
some isolated showers as it interacts with a moisture/instability
axis over the Mondak region. Expect these showers to dissipate as
they move east into more stable atmosphere over central ND.

The next shortwave looks to be a little slower than previously
forecast. Latest iterations of short range models have pushed
development of showers and thunderstorms to around midnight or
later. Will keep a minimal pop over the northwest this evening but
it looks like better chances will slide from northwest into
central ND during the overnight hours as the low level jet spreads
eastward.

On Wednesday, any shower or thunderstorm activity lingering in the
central is expected to diminish during the morning hours. Focus
then shifts back to the west, and fire weather issues, as the low
level jet becomes re-established over the west ahead of a deep
upper trough and its associated surface development over eastern
montana. See fire weather discussion below for details on fire
weather issues.

Thunderstorm activity shifts north and west of the area Wednesday
through Thursday afternoon. Thunderstorm activity increases
Thursday evening, and again Friday afternoon and night as the
upper level ridge moves east of the area and strong forcing with
good instability move over western and central North Dakota. Best
forcing and less cap will be situated over the west central
through north central.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 251 PM CDT Tue Aug 30 2016

Main highlight is increasing chances for precipitation through the
long term period.

Showers and thunderstorms look to increase in areal coverage
Saturday as a cold front slowly moves from west to east during the
day, not exiting the southern James River Valley until late Saturday
night. Per GFS/ECMWF, the strongest 0-6km bulk shear increases
behind the front, in excess of 40kt to 60kt; while along and ahead
of the front, shear weakens from 30kt to 20kt. Most unstable cape
between 1500-2500 j/kg along and ahead of the front and given shear
values near 30kt, strong to severe thunderstorms possible for
central ND. The ECMWF is less robust with precipitation during the
day, but increases the coverage Saturday night.

For Sunday through Labor Day Monday, the GFS and ECMWF diverge with
regards to precipitation. The gridded forecast data is closer to the
ECMWF solution, which depicts the cold front stalling across South
Dakota and low pressure developing and riding up along the front
with chances for showers continuing Sunday through Sunday night.
The GFS is much drier for Sunday as it shunts the showers farther
east. Both models continue to indicate a slow moving mid/upper level
trough approaching from Northern Rockies Sunday night which will
propagate across western and central ND Monday through Tuesday.
Both solutions yield another round of showers increasing from west
to east on Labor Day, and continuing Monday  night. Although
sufficient 0-6km shear is present, cape is limited to 200-500 j/kg
in the far south, so any threat for thunderstorms should be limited
at best. The ECMWF is slower with this system keeping decent chances
of precipitation going through Tuesday, while the GFS is faster in
moving this upper trough and indicating drying conditions taking
place Tuesday. The gridded data continues to resemble the ECMWF or
wetter solution. It will be cooler with highs in the mid to upper
60s Monday and Tuesday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 634 PM CDT Tue Aug 30 2016

Isolated to scattered thunderstorms possible overnight into
Wednesday morning over western and central North Dakota.
Otherwise...VFR conditions expected.

&&

.FIRE WEATHER...
Issued at 251 PM CDT Tue Aug 30 2016

Fire weather concerns are heightened on Wednesday and Thursday. On
Wednesday, 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 mph with gust 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 the moisture advection into the southwest.
We could still mix out a bit today but relative humidities are
about 5 to 10 percent higher than forecast. If we do realize our
forecast afternoon minimum humdities...think we will see fire
weather highlights. If, like today, dewpoints remain higher than
forecast, it will be harder to reach critical fire weather
conditions. Will let the evening and overnight shifts monitor for
possible fire weather watch/warning for Wednesday.

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. 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...
NONE.
&&

$$

UPDATE...JJS
SHORT TERM...TWH
LONG TERM...KS
AVIATION...JJS
FIRE WEATHER...TWH



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