Area Forecast Discussion
Issued by NWS Rapid City, SD

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331
FXUS63 KUNR 202328
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
528 PM MDT Sat May 20 2017

.DISCUSSION...(This Evening Through Saturday)
Issued at 229 PM MDT Sat May 20 2017

Deep closed low over the Rockies continues to slowly shift NE
with backside impulses expected to affect the region the next
couple days. Main forcing and associated FGEN from the upper low
will exit the FA late this afternoon and evening with rain ending
over scentral SD. Skies will clear tonight with light winds and
dry air in place supporting a very good radiational cooling setup
tonight. This will support the development of areas of frost, esp
in areas protected from the wind. Next impulse/jet streak will
affect the region Sunday afternoon, with diurnal heating and steep
lapse rates supporting sct shra/isold TS in the afternoon.
Moisture will be highly limited in dry NW flow, with most shra not
amounting to much. Stronger trailing impulse will then arrive
Sunday night into Monday and support another round of sct
shra/isold TS. Continued cool conds expected through Monday.

Upper low will push east by mid week with deep layer ridging
expected. This will bring much warmer weather and dry conds to the
region for a couple days. Forecast models are more aggressive
with NW CONUS toughing and now introduce a leading SW flow impulse
Thur. Hence precip chances return to the forecast as early as
Thur, however better chances toward the weekend. Moisture looks to
be limited with this next round of troughing given closed GOMEX
and PAC origin flow.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening)
Issued At 527 PM MDT Sat May 20 2017

Leftover MVFR CIGS/-RA will end over south central SD this
evening. Otherwise, VFR conditions expected through the period.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Frost Advisory from midnight MDT /1 AM CDT/ tonight to 7 AM MDT
     /8 AM CDT/ Sunday for SDZ001-002-012>014-025>027-030>032-
     041>044-046-047-072>074.

WY...Frost Advisory from midnight tonight to 7 AM MDT Sunday for
     WYZ054>056-058-071.

&&

$$

DISCUSSION...JC
AVIATION...Helgeson



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