Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 171726

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1126 AM MDT Sat Mar 17 2018

.DISCUSSION...(Today Through Friday)
Issued at 200 AM MDT Sat Mar 17 2018

Overall, very typical early spring-like weather will prevail for
the next week as the weather pattern remains unsettled, resulting
in mixed precipitation types and some up and down temperature
excursions. Models are struggling on the details of precipitation
type, but agree fairly well on the synoptic evolution.

A somewhat complex upper-air pattern existed this morning with a
large low over OR/CA/NV and yesterday`s low shearing out over IA/MO.
The western low will move to KS/OK by Monday morning as another
weak low meanders across eastern MT. Today, ahead of this low,
850-mb temperatures will rebound nicely across the CWA leading to
a brief warm-up -- especially where snow cover is minimal. Have
thus went with highs near guidance for snow-free areas but on the
low end of guidance for snow-covered areas. Also for today, low
clouds and fog will be widespread early this morning, especially
across western into central SD. These should slowly mix out
throughout the morning into early afternoon.

Some showers will develop after 06z tonight as a lead short-wave
trough ejects out of the western U.S. trough. Given the warm low-
levels, this will result in a wintry mix of precipitation. This
area of precipitation will expand across the area Sunday, with the
wintry mix continuing. Depending on thermal profiles, some notable
snow could fall over parts of the Black Hills through northwestern
SD, but uncertainty in precipitation type is high at this time.
Rain and snow will continue across the CWA Sunday night and Monday
as the main low goes to our south and the weaker upper low is
somewhat stalled over eastern MT.

The showers will become more isolated Monday night and Tuesday as
ridging starts to develop over the western CONUS and the MT low
shifts eastward a little. Tuesday night through Thursday should be
mostly dry with a warming trend, albeit the GFS appears to be an
outlier in bringing showers across the area on Thursday. Otherwise,
all models agree on a rather unsettled weather pattern returning for
Friday through next weekend, although it appears to be warmer and,
thus, with mostly rain on Friday.


.AVIATION...(For the 18Z TAFS Through 18Z Sunday)
Issued At 1126 AM MDT Sat Mar 17 2018

MVFR cigs will persist over portions of the SD plains through
early this afternoon before gradually eroding. VFR conditions are
then expected area-wide through early evening.

Continued light to moderate winds overnight will likely preclude
widespread dense FG development through Sunday morning, but
MVFR/IFR cigs and potentially MVFR vsbys are still expected for
much of the area overnight.

Reduced cigs/vsbys will continue through much of Sunday as a light
wintry mix overspreads the area. Details on timings and
precipitation types will be ironed out in subsequent TAFs.




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