689 
FXUS63 KUNR 171043
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
443 AM MDT Sun Sep 17 2017

.DISCUSSION...(Today Through Saturday)
Issued at 237 AM MDT Sun Sep 17 2017

Latest analysis shows upper low over SK/MB swinging an upper
trough across the eastern Dakotas and yet another weak upper
trough over the western CONUS. At the surface, cool high pressure
is centered over SD. May still see some patchy frost in protected
low lying areas this morning, although due to the recent 
rainfall, dewpoints at most locations are remaining in the mid 
30s and mid level warm air advection is developing over the
western parts of the forecast area early this morning.

For today, warmer temperatures are expected with breezy southerly
winds developing in the tightening surface pressure gradient
between the departing sfc high and a sfc trough strengthening on
the east side of the Rockies. A weak shortwave will cross the area
late this afternoon and evening. There may be enough low level
moisture return for a slight chance of thunderstorms over far
southwestern South Dakota, however only isolated thunderstorms are
expected with minimal rainfall amounts.

Monday will be even warmer as a short-wave ridge and low-level 
thermal ridge cross the area. Southerly winds are expected to be  
breezy again during the afternoon and into Tuesday morning. A 
strong upper trough will cross the area Tuesday aftn/night, which
will be preceded by a cold frontal passage Tuesday. The GFS
remains the outlier, being about six hours faster than the 
NAM/GEM/ ECMWF/MPAS models. This should lead to a band of 
scattered SHRA moving across much of the area Tuesday afternoon 
and evening.

A large upper trough will then become established over the western 
CONUS by Thursday with an unsettled weather pattern across the 
central plains due to continued southwesterly flow aloft.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 437 AM MDT Sun Sep 17 2017

Scattered low clouds are dissipating across the CWA this morning. MVFR
conditions will be possible in showers/storms today across 
southwestern into west central SD. Otherwise, VFR conditions are 
expected through the period.

&&

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

$$

DISCUSSION...10
AVIATION...Pojorlie