Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 151840
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1140 AM MST Wed Nov 15 2017

.DISCUSSION...(Today Through Tuesday)
Issued at 218 AM MST Wed Nov 15 2017

09z surface analysis had low pressure over northern MN with main
cold front into western OK and secondary trough into northwest SD.
Band of ST just behind the trough will affect far northwest SD
this morning. Water vapour had upper trough east of the CWA with
upper ridge building over the Rockies toward the CWA.

Today and tonight, normal weather expected. ST over the far north
will exit the CWA. Return flow begins over northeast WY and
intensifies tonight as low level warm air advection perks up.
Temperatures will be near guidance.

Thursday, upper ridge moves into the northern Plains with thermal
ridge peaking over the CWA. Pressure falls over the Dakotas will
support gusty west/southwest winds at times, especially over the far
southwest where gusts may surpass 40 MPH at times. Some guidance
suggests high wind warning criteria could be met across southern
Campbell into Weston County, but that would require full mixing
to 700mb which will have 50-60kt winds. Further shifts will need
to look at model trends. Temperatures will be 10-20F above normal
Thursday.

Thursday night into Friday, pre-frontal trough moves through the CWA
as upper trough approaches from the west Thursday night. Cold front
moves through the CWA Friday with much cooler temperatures. Should
be a narrow band of frontogenesis associated with front, but
moisture availability big question. GFS quite wet with several
inches of snow possible given wet bulbs, but other guidance much
drier. Consensus tilts toward low QPF, so will continue with this
thinking.

Saturday into early next week, weakly amplified upper ridge
dominates with little moisture and forcing supporting a dry forecast
and near normal to slightly above normal temperatures.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1139 AM MST Wed Nov 15 2017

VFR conditions are expected through the period. As southwesterly
flow increases tonight, some low-level wind shear will be possible
across parts of the area.

&&

.FIRE WEATHER...
Issued At 218 AM MST Wed Nov 15 2017

Gusty west/southwest winds expected Thursday with minimum
relative humidities in the 20s creating elevated fire danger.
Colder and moister air settles into Thursday night into Friday as
a cold front moves through.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...Helgeson
AVIATION...15
FIRE WEATHER...Helgeson



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