167
FXUS63 KUNR 141806
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
1206 PM MDT Wed May 14 2025

.KEY MESSAGES...

- Slight risk of severe thunderstorms over south-central SD this
  afternoon/evening
- Wind gusts in excess of 60 mph possible Thursday on the western
  SD plains
- Strong storm system brings more chances for beneficial
  precipitation early next week

&&

.DISCUSSION...(Today Through Tuesday)
Issued at 210 AM MDT Wed May 14 2025

08z surface analysis had cold front from eastern ND through
western NE connected to a low over far southwest NE. Water vapour
loop had upper trough from MT into NV with 100kt jet streak on the
front edge which was assisting convection over the CWA early this
morning per KUDX WSR-88D. Early morning SPC mesoanalysis had
~1KJ/kg MUCAPE/40kt effective bulk shear, which has been
sufficient for isolated strong/marginally severe storms. Expect
activity to continue northeast overnight and slowly weaken.
Attention then turns to upper trough and resultant surface low.

Today/tonight, jet streak on leading edge of upper trough creates
a compact upper low over the CWA by 12z Thursday. Southwest NE
low deepens as it moves along cold front and occludes. This will
tighten frontal boundary this afternoon, pulling up upper 50s Td/s
into south-central SD with 1-2KJ/kg MLCAPE/increasing 0-6km bulk
shear (35-40kts). Per CAMs, this should be sufficient for a line
of thunderstorms with embedded severe thunderstorms over south-
central SD later in the afternoon/early evening, quickly moving
away from the CWA. Large hail/damaging wind will be the main
threat. Further west, less robust convection expected with low
confidence on where it will occur/QPF amounts. PWATs increase to
150-200% of normal along cold front, which may be sufficient for
locally heavy rainfall over an area of D1-2 drought. Temperatures
will be tricky today/tonight, so didn`t stray from guidance.

Thursday, tight pressure gradient as stacked low over eastern ND
spins. Backwash moisture will support PoPs over the CWA, but QPF
amounts look relatively light except near the ND border. 800-700mb
mean wind 40-60kts with forecast soundings/MOS guidance pointing
toward the potential for wind gusts in excess of 50kts. NBM has
50-80% chance of >55 MPH wind gusts. Have hoisted High Wind Watch
to account. Temperatures will be seasonal.

Friday/Saturday, a couple of shortwave troughs/ridges move
through as upper trough is carved out over the Rockies. Fleeting
convection is possible. Deep southwest flow Sunday ahead of upper
trough and then strong upper trough/low moves over the CWA
Monday/Tuesday. Significant/highly welcome QPF is looking more
probable (Sunday through Tuesday) along with the potential for
active convection ahead of the upper low and the potential for
snow behind it over the higher elevations. EFI shift of tails for
snow has values as high as 5, which suggests some members are
giving significant snow for parts of the CWA. Current forecast
isn`t that aggressive and impacts will probably be minor, but
something to watch.

&&

.AVIATION...(For the 18Z TAFS Through 18Z Thursday)
Issued At 1136 AM MDT Wed May 14 2025

MVFR CIGS will prevail over northeastern WY/far western SD most
of the forecast period. TSRA will be developing, throughout the
afternoon, east of the Black Hills over central SD, some of which
will contain hail, strong gusty erratic winds, and IFR
conditions. Inbetween and outside of TSRA, VFR conditions early
this afternoon will give way to MVFR/IFR conditions later tonight.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...High Wind Watch from Thursday morning through Thursday evening
     for SDZ001-002-012>014-025-031-032-043-044-046-047-072-073-
     077-078.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...Schultz