Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 181723
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1123 AM MDT SUN SEP 18 2016

.SHORT TERM...(Today Through Monday Night)
Issued at 230 AM MDT Sun Sep 18 2016

Current surface map shows low pressure across Saskatchewan with
trof into the northern plains. 130kt jet streak located across
the Pacific Northwest will move eastward along the Canadian border
today, allowing weak cold front to slip through the western
Dakotas. Deep mixing will result in gusty northwest winds, with
the strongest winds across northwest South Dakota. Will be near
advisory criteria this afternoon, mainly along the North Dakota
border. Combination of wind and low relative humidity will put
Grassland Fire Danger Index into the extreme category for much of
northwest South Dakota and far southwest South Dakota. Lowest
relative humidity will be across southern portions of Campbell
County into Fall River County. That area may approach Red Flag
conditions this afternoon.

For tonight, models have been showing a light precipitation event
for far northwest South Dakota for several days. However, latest
runs backing off on upper forcing and also maintaining drier air
below 5000 ft agl. Have trimmed back pops overnight but did keep
some mention of sprinkles late tonight. Surface high sets up
across northern South Dakota for Monday.

.LONG TERM...(Tuesday Through Saturday)
Issued at 230 AM MDT Sun Sep 18 2016

Very warm temperatures are expected on Tuesday, as upper ridge
amplifies slightly over the region. A surface low will begin
moving through the Dakotas. With southwesterly winds over the
southern half of the CWA and easterly winds over the northern half
of the CWA, highs will range from the mid 70s across northwestern
SD to near 90 across southwestern/south central SD. A weak wave
will pass through the upper ridge dry late Tues/Wed, although
cooler air will be pulled into the area. Highs Wed will cool to
the 70s and lower 80s.

A Pacific Northwest upper low will slowly approach the region
towards the end of the week. The 00Z runs of the GFS and ECMWF are
in better agreement than previous runs; however, there is still some
uncertainty on track of the low and whether the CWA will receive
significant moisture or be dry-slotted. As the low slowly crosses
the region next weekend, strong winds will also be a possibility.
Temperatures for the end of the week and into next weekend will be
below average.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1121 AM MDT Sun Sep 18 2016

Breezy northwest winds will decrease early this evening. VFR
conditions are expected through the forecast period.

&&

.UNR Watches/Warnings/Advisories...
SD...None.
WY...None.
&&

$$

SHORT TERM...7
LONG TERM...Pojorlie
AVIATION...13



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