Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 231140

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
540 AM MDT Fri Mar 23 2018

.DISCUSSION...(Today Through Thursday)
Issued at 257 AM MDT Fri Mar 23 2018

The latest upper analysis shows the upper ridge has shifted
slightly eastward, now over the eastern Dakotas/Nebraska, leading
to strong WAA in southwesterly flow aloft over the forecast area.
At the surface, a tight surface pressure gradient associated with
a low pressure center over north central Wyoming was producing
breezy to windy southeasterly winds over the forecast area. The
region of strongest lift associated with the WAA aloft is
currently producing precipitation over the eastern parts of the
forecast area early this morning. Most areas are experiencing
rain, but over parts of northwestern South Dakota there is a
transition zone to a brief period of light freezing rain, then to
snow as the precipitation falls into a deeper region of cold air
toward north central South Dakota. Any ice accumulations are
expected to remain minimal this morning with an inch to locally 2
inches of snow possible toward north central South Dakota early
this morning. The moist southeasterly upslope flow is also
producing areas of fog over western SD this morning.

The main band of precipitation will lift off to the northeast of
the forecast area this morning, but there will be enough
instability for some showers through much of the day today and
especially this afternoon, as an upper shortwave crosses the
area. Isolated thunderstorms will be possible near and south of
the Neb/SD border this afternoon.

A short wave ridge behind the departing system will bring dry
weather for Saturday, but southwesterly flow aloft will return by
Saturday evening as a large scale trough over the western CONUS
slowly crosses the Rockies. There is a chance of showers on
Saturday night and Sunday with rain or snow likely on Sunday night
and Monday. Dry weather is expected Tuesday with only limited
chances of rain showers or snow showers on Wednesday and Thursday.

Temperatures will be near average through the period.


.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 532 AM MDT Fri Mar 23 2018

Widespread fog will persist across much of far western and
northwest South Dakota this morning, with IFR/LIFR conditions
through 16-18Z. A cold front will move through during the late
morning hours and switch winds to the northwest and help dissipate
the fog. Improvement to flight conditions is expected during the
afternoon as drier air moves in behind the front. Isolated showers
will be possible this afternoon, with thunderstorms possible near
the SD and Nebraska border.




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