Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 242324

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
524 PM MDT Sun Sep 24 2017

.DISCUSSION...(This Evening Through Sunday)
Issued at 121 PM MDT Sun Sep 24 2017

The latest observations showed an upper low across northeastern
UT with a short-wave wave rotating through northern CO. Relatively
dry air aloft was in place across much of the CWA, but low clouds
covered most all of the area. Radar returns were noted across
central/southeastern WY moving toward the CWA, while the other
area of showers had moved east of Tripp County.

Models agree well that the upper low over CO/UT/WY will send the
short-wave trough across the CWA tonight and early Monday morning
as the upper low moves to central WY. The upper low will then move
northeast on Monday to northwestern ND by Tuesday morning. This
will result in another round of scattered showers moving across
the area tonight (which the HRRR/HRRR-EXP seem to capture well),
but overall rainfall amounts will be light as PWAT values fall
back to average or below. Some light snow also will be possible in
the highest Black Hills. Isolated to scattered showers will occur
again Monday as the upper low moves just northwest of the CWA,
with showers possibly lingering through Monday night. Also, if
skies clear out enough Monday night there will be areas of frost
on Tuesday morning, especially across far southwestern SD.

The upper low will then move northeast Tuesday and Tuesday night
with building heights and drier/warmer weather developing. Models
then show a short-wave trough Wednesday night and Thursday in
northwest flow, although this looks to be fairly dry and week. Weak
upper ridging to split flow is then advertised Friday into Saturday,
with seasonal temperatures.


.AVIATION...(For the 00Z TAFS Through 00Z Monday Evening)
Issued At 519 PM MDT Sun Sep 24 2017

Widespread IFR conditions are expected tonight. Isolated to
scattered showers are expected. LIFR conditions are expected over
parts of northeastern Wyoming, the Black Hills and over parts of
southwestern and south central South Dakota. Conditions will
improve to MVFR over most areas by 17Z on Monday with VFR
conditions developing over most of the area by 20Z on Monday




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