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000
FXUS63 KUNR 202256
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
456 PM MDT Tue Apr 20 2021

.DISCUSSION...(This Evening Through Tuesday)
Issued at 151 PM MDT Tue Apr 20 2021

Long-wave trough currently dominates much of the CONUS weather as
small short-wave troughs move south across the northern high
plains. Diurnally driven heating at the surface combined with a
cold pool aloft was fostering scattered/numerous convective snow
showers across much of the CWA. As heating wanes and the large-
scale trough axis shifts southeast this evening, snow showers
should come to an end, and northwest winds also should diminish.

Models/ensembles agree very well on the large-scale evolution
through much of the forecast period. Tomorrow and tomorrow night
will feature rising heights with return southerly surface flow
developing. Temperatures also will be moderating. A low over the
Southwest U.S. will move to east-central WY by 12z Thursday,
spreading some snow/rain showers toward south-central SD on
Thursday where a low-level jet and WAA will focus ascent. On
Thursday night and Friday, an elongated upper trough will
approach the CWA, ushering in a frontal passage Thursday night.
This will be followed by CAA and gusty northwest winds on Friday,
along with scattered showers (mostly snow). Moisture,
instability, and lift do not appear to be as substantial with this
Friday system as with the current system, so expect less coverage
and amounts overall. On Friday night and Saturday, the upper
trough axis shifts east and a subtle upper ridge builds over the
area. This should lead to temperatures getting back to near- (or
even above) average for Saturday-Monday. Return southerly flow
and a low-level jet with WAA may support some showers over south-
central SD late Saturday night, but confidence is rather low at
this point. Otherwise, better chances of more widespread
precipitation (mostly rain, at this time) appear in order by late
Monday and Tuesday as a large upper trough moves across the
Southwest U.S. and deep southwest upper flow affects the CWA.
Again, models/ensembles agree rather well on this evolution.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening)
Issued At 455 PM MDT Tue Apr 20 2021

Isolated/scattered SHSN will continue through early this evening
with local MVFR/IFR CIGS/VSBYS at times. SHSN will taper off as
skies clear overnight allowing VFR conditions to prevail by
Wednesday morning.

&&

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

$$

DISCUSSION...Bunkers
AVIATION...10