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Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
1125 PM MDT Sat Aug 29 2015

Short term...this evening through Sunday night
issued at 258 PM MDT Sat Aug 29 2015

Current surface analysis shows low pressure over sk...with a cold
front trailing southwestward into northwest Montana and northern Idaho. A
surface trough extends southward across eastern Montana into northeast
Wyoming. Upper level analysis shows ridging over The Rockies and into
the High Plains. Flow aloft has become westerly over the area and
will become southwesterly into tonight. Temperatures are in the 90s
across the plains...with 80s in the Black Hills. Winds are south
to southwest...breezy across portions of northeast Wyoming. Hazy
sunshine continues through the smoke...though conditions appear to
be gradually improving in most areas this afternoon.

As ridge builds over and east of the area through the weekend...hot
conditions can be expected. The cold front to the northwest of the
region will eventually make it into the forecast area late Sunday
and Sunday night...bringing mostly isolated showers and
thunderstorms...along with cooler and breezy conditions behind it
into Monday.

For tonight...skies will stay mainly clear with lows mostly in the
60s to around 70 degrees. Low level southerly jet will intensify
over the area overnight...with breezy conditions at times in the
usual areas from northeast Wyoming through southwest into south central
South Dakota. Atmosphere looks too dry to get any showers to develop with the
jet.

Sunday will see mostly sunny to partly cloudy skies with highs in
the 90s to around 100 degrees on the plains as the thermal ridge
moves across western into central South Dakota during the day. Exact timing of
the cold front is still a bit uncertain...but it should move into
northeast Wyoming late in the day and across the rest of the forecast
area Sunday night. Winds will switch to the west-northwest and
become breezy to windy across northwest into west central South Dakota
overnight. Embedded energy in southwest flow aloft will combine with
the front to produce at least isolated showers and storms over a
good portion of the County Warning Area Sunday night. The threat for strong to
severe storms is minimal with the timing of the front...though winds
could get gusty with some of the showers behind the front.

Long term...Monday through Saturday
issued at 258 PM MDT Sat Aug 29 2015

Negative height anomaly over the Pacific northwest will remain nearly
stationary through the period...with generally warm conds over the
northern plains as upper level SW flow persists. The western noam
upper trough will gradually shift east as a stronger northern
stream impulse merges with it...leading toward breakdown of the
persistent ridge. In the meantime...above normal temperatures will
persist through most of the period...with mainly dry conds. Weak
cold front will advect through the area Monday morning...
supporting cooler but still seasonal temperatures in a cold air advection regime Monday.
Central noam ridge will re-surge Tue-thur...with very warm conds
expected once again as southerly flow spreads over the region.
Weak SW flow impulses could support a few isolated rain showers/ts in the
Tuesday-Wednesday period...especially with any concentrated positive Theta-E advection.
However...lack of any appreciable signals preclude any pop
mention. Northwest Pacific upper trough will bias east by the end of the week
with cooler weather looking more likely with increasing chances
for rain.

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1124 PM MDT Sat Aug 29 2015

VFR conditions will prevail through Sunday afternoon. Low level
wind shear is expected on the South Dakota plains through Sunday morning as
a low level jet from 30-40kts occurs. Isolated -tsra possible
over the far west late Sunday afternoon/evening.

&&

Fire weather...
issued at 258 PM MDT Sat Aug 29 2015

Warm and dry conds will persist across NE Wyoming. Relative humidity
across portions of the northeast Wyoming plains will drop to 15
percent or below this afternoon and again Sunday afternoon. Gusty
southwest winds will continue through Sunday...and are expected to
be strongest Sunday afternoon ahead of a cold front. SW winds of
20 to 30 miles per hour with gusts to around 35 miles per hour are expected sun.
Partially mixed conds can be expected tonight given pressure
falls...with SW winds continuing under poor relative humidity recovery. Went
ahead and extended the red flag warning through Sunday afternoon
for this.

&&

Unr watches/warnings/advisories...
South Dakota...none.
Wyoming...red flag warning until 8 PM MDT Sunday for wyz259-297-298.

&&

$$

Short term...26
long term...jc
aviation...helgeson
fire weather...jc

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