Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 171136

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
536 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 12Z TAFS Through 12Z Sunday Morning)
Issued At 536 AM MDT Sat Mar 17 2018

Areas of MVFR/IFR conditions will persist across far northeast
WY,the Black Hills, and far southwest SD early this morning, with
more widespread IFR/LIFR conditions across the rest of the western
SD plains. Areas of fog can also be expected through mid morning.
Conditions will become mainly VFR across the area by 18z and
persist into this evening. Areas of MVFR/IFR conditions will
likely redevelop overnight/early Sunday as the next upper level
system approaches, especially across northeast WY and the Black
Hills area.




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