Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 251954
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
154 PM MDT Thu May 25 2017

.DISCUSSION...(This Evening Through Thursday)
Issued at 151 PM MDT Thu May 25 2017

19z surface analysis had low over southern SK with cold front
through eastern ND/central NE. Another trough behind low into
central MT. Water vapour showed weak shortwave/shear axis from
northwest ND into central WY. Slightly steeper lapse rates under
this wave contributing to CU per visible satellite image from
southwest ND into northeast WY. Have introduced smallish PoPs for
this area given very weak instability and convective allowing
models suggesting a few sprinkles/-SHRA possible through this
afternoon. Attention then turns toward upper low over SK with
trough into the central Rockies.

Tonight, aforementioned disturbance moves through CWA with some
clouds. Some guidance showing weak returns over southern SD
overnight, but not seeing forcing or moisture sufficient for
mentionable PoPs at this time. Lows will be near guidance.

Friday into Saturday morning, upper lows spins into central Canada
as a decent chunk of energy whips around it across the central
Rockies into the central Plains. Synoptic scale lift ahead of the
wave begins Friday afternoon and ramps up Friday night into Saturday
morning across mainly the southern portions of the CWA. Moderate
frontogenesis noted, but main convective instability south of the
CWA. Guidance is in agreement on a strip of decent rains along the
SD/NE border with lesser amounts to the northern. Temperatures will
be near guidance.

Saturday afternoon into Sunday, main upper trough moves east with
northwest flow aloft. Low level instability develops during peak
heating and may result in mainly diurnal -SHRA/TS chances.
Temperatures will be near guidance.

Monday through Wednesday, modest upper ridge will bring a slow
warm-up. Should be mostly dry, except perhaps by Wednesday when a
decent shortwave/cold front could move through the CWA.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Friday)
Issued At 1202 PM MDT Thu May 25 2017

VFR conditions are expected through the forecast period. Breezy
northwest winds mainly across northwest SD will decrease this
evening.

&&

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

$$

DISCUSSION...Helgeson
AVIATION...13


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