Area Forecast Discussion
Issued by NWS Rapid City, SD

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398
FXUS63 KUNR 161932
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
132 PM MDT Sat Sep 16 2017

.DISCUSSION...(This Evening Through Saturday)
Issued at 127 PM MDT Sat Sep 16 2017

A large trough seen on water vapor images over MT/WY will move
past the CWA this evening. A few showers were moving through NWRN
SD with one short-wave trough while some TSRA were moving through
ECNTRL WY with another short-wave trough and a small pocket of
MLCAPE of 100 J/kg. Short-term convection-permitting models are
consistent with moving this area of TSRA into far SWRN SD before
dissipating early this evening.

Otherwise for tonight, expect some areas of frost with 850-mb
temperatures of around 5C and surface high pressure across the CWA.
The main hinderance to frost will be considerable low-level moisture
and potentially clouds that will limit cooling. Thus, only expect
frost to be patchy, with the Pine Ridge area likely the coldest.

Models are then in very good agreement with warmer and drier weather
for Sunday. They also agree well with a low-amplitude short-wave
trough moving across ERN WY and WRN SD during the afternoon and
evening. Given limited moisture and forcing, only isolated TSRA is
expected with minimal rainfall amounts.

Monday will be even warmer as a short-wave ridge and low-level
thermal ridge cross the area. South winds also could be a bit
breezy during the afternoon and into Tuesday morning. A strong
trough will then move across the area Tuesday night, which will be
preceded by a cold frontal passage Tuesday. The GFS definitely is
an outlier here, 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 owing to southwest flow aloft.

&&

.AVIATION...For the 18Z TAFS Through 18Z Sunday
Issued At 1136 AM MDT Sat Sep 16 2017

MVFR/IFR CIGS will continue to gradually improve to VFR this
afternoon and evening as skies clear out. VFR conditions are
then expected through Sunday morning.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Frost Advisory from midnight tonight to 8 AM MDT Sunday for
     SDZ001-002-012>014-025-030>032-041>043-072-073.

WY...Frost Advisory from midnight tonight to 8 AM MDT Sunday for
     WYZ054>056-058-071.

&&

$$

DISCUSSION...Bunkers
AVIATION...13



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