Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 222002
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
202 PM MDT Sat Jul 22 2017

.DISCUSSION...(This Evening Through Saturday)
Issued at 134 PM MDT Sat Jul 22 2017

Latest upper analysis shows an upper low center over Winnipeg
swinging a weakly defined upper trough across the forecast area.
An associated surface boundary is currently moving into
southwestern/south central South Dakota, aiding the development of
isolated showers and thunderstorms there. Weak low and mid level
cold advection behind the surface boundary is combining with
diurnal heating to increase the depth of the mixed layer, leading
to breezy northwesterly winds over northwestern South Dakota.

The upper ridge will continue to build and broaden, leading to dry
and warm weather tonight and on Sunday. Modest low level jet will
develop on Sunday night which may lead to localized, elevated
convection.

On Monday the upper and thermal ridge will peak over the forecast
area ahead of a cold front. Readings near 100F likely on Monday
afternoon, especially if southwesterly downslope flow develops in
the afternoon. Some thunderstorms are possible on Mon aftn/night
as the cold front crosses the area.

Progressive upper flow is expected through much of next week with
a series of upper shortwaves and sfc fronts cross the forecast
area and bringing low chances of precip. The models continue to
show Wednesday as having the best chance of more widespread
showers and thunderstorms. Temperatures will be noticeably cooler
by mid-week given expected increased cloud cover and higher RH
and PoPs.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 134 PM MDT Sat Jul 22 2017

Isolated showers will continue to cross south central SD this
afternoon before dissipating or moving out of the area. Smoke
from fires in central Montana may result in periods of MVFR
visibility at times. Otherwise VFR conditions are expected.

&&

.FIRE WEATHER...
Issued at 134 PM MDT Sat Jul 22 2017

Breezy winds are developing over northwestern South Dakota as
diurnal heating increases the depth of the mixed layer. Relative
humidity has already fallen to around 15 percent in many areas so
will keep the Red Flag Warning in place over northwestern South
Dakota. Conditions will improve early this evening.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning until 7 PM MDT this evening for SDZ261-266.

WY...None.
&&

$$

DISCUSSION...10
AVIATION...13
FIRE WEATHER...10



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