Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 222028
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
228 PM MDT Sun Apr 22 2018

.DISCUSSION...(This Evening Through Sunday)
Issued at 224 PM MDT Sun Apr 22 2018

Weak upper ridging exists over the northern plains,
and the next shortwave to affect the region is over the Pacific
Northwest. Satellite shows mostly clear skies over the CWA. A cold
front extends from a Canadian low, just northwest of SD, where it is
expected to move little until Monday. Winds are from varying
directions around 5 to 10 kts, and temperatures are rising into the
60s.

Upper shortwave will strengthen as it approaches the northern plains
Monday. Warm air will advect into the western SD plains ahead of the
low, and temperatures there will rise into the 60s. However, western
parts of the CWA will remain cooler, as a cold front begins to sweep
through the area.

Precipitation will spread into the region behind the cold front
as rain, with some thunderstorms possible in the afternoon across
the southwestern CWA. Models are aligning more with yesterday`s
more northerly GFS, keeping the higher QPF amounts mainly over
northwestern and north central SD, where around an inch of liquid
precipitation may fall. They are also agreeing better on timing,
with precip lingering across south central SD until Tuesday night.

As cold air filters into the region behind the front, rain will
change to snow across northeastern WY and far western SD. Just a few
degrees of a change in temperature could make a big difference in
snow amounts; ensemble snowfall spreads vary greatly. Additionally,
actual snow accumulation will be tricky, given recently warm surface
temps. With models leaning towards a more northerly track of the
low, forecast snow amounts have decreased across northeastern WY and
the northern Hills, and increased across northwestern SD. Could see
generally 1-3 inches on the plains, and up to 5 inches in the Hills.

Gusty northwest winds will accompany the cold front, although the
highest pressure rises of 6-8 mb/3hr won`t arrive until after
sunset. Nonetheless, expecting sustained winds around 30 kts just
east of the Black Hills, which may be worth headlines if the trend
continues.

Following the Monday/Tuesday system, another wave will bring some
cool temps, breezy winds, and light showers to the area Thursday.
But other than that, upper ridging will keep weather generally mild
and dry for the rest of the week.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Monday)
Issued At 1109 AM MDT Sun Apr 22 2018

VFR conditions are expected over western SD through Monday
morning. VFR conditions are expected over northeast WY through
tonight, but then as a storm system approaches, MVFR CIGS will
develop by 18z Monday along with some -SHRA.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&

$$

DISCUSSION...Pojorlie
AVIATION...Helgeson


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