Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201127
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
527 AM MDT Sun May 20 2018

.DISCUSSION...(Today Through Saturday)
Issued at 224 AM MDT Sun May 20 2018

08z surface analysis had weak high over the northern Plains.
Upper low spinning over northern central NE per water vapour loop.
It was spinning mid/high clouds over most of the CWA with some
leftover stratus across northeast WY and south central SD.

Today and tonight, upper low continues to weaken as it moves into
eastern SD. Upper trough over the western CONUS deepens with upper
low over developing over central CA. Surface high shifts east with
return flow/few breezy spots expected. Temperatures will be near
guidance.

Monday through Wednesday, CA upper low moves through the Rockies
into southern SK. Upper ridge develops ahead of it over the central
US with southwest flow aloft over the CWA. Temperatures will be
about 10F above normal for Tue/Wed as thermal ridge peaks. Moisture
will slowly increase during the period with sustained southeasterly
boundary layer flow. Weak shortwave moves through Monday with
stronger system for later Tuesday into Wednesday. Fairly low
coverage TSRA expected late Monday with better coverage expected
Tuesday night into Wednesday. Moderate MLCAPE and marginal 0-6km
bulk shear will combine to perhaps bring a strong TSRA to the CWA
Tuesday afternoon/evening.

Thursday through Saturday, upper low shifts east as an upper
trough across southern Canada as upper ridge develops over the
western CONUS. CWA will transition to drier northwest flow with
subsequent reduction in PoPs. Temperatures will be 5-10F above
normal.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 526 AM MDT Sun May 20 2018

VFR conditions through the period. Breezy SE winds can be
expected over NE WY today and over western SD by this afternoon.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...15


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