FXUS63 KUNR 091051

AFDUNR



Area Forecast Discussion For Western SD and Northeastern WY

National Weather Service Rapid City SD

451 AM MDT Fri May 9 2025



.KEY MESSAGES...



- Near record/record high temperatures Sunday/Monday

- Thunderstorm chances this afternoon, and then Sunday evening 

  through most of next week

- Elevated fire weather conditions Saturday through Tuesday



&&



.DISCUSSION...(Today Through Thursday)

Issued at 159 AM MDT Fri May 9 2025



07z surface analysis had weak surface trough from central ND to 

KD07 to central WY. Water vapour showed weak shear axis across the

northern Plains coincident with surface trough, as well as upper 

ridge building from the southwest CONUS into the northern Plains. 

Radar returns are meager with very isolated showers over the far 

northwest. Short term forecast concern is surface trough.



Today/tonight, surface trough shifts southward, stalls, and then 

becomes a warm front over eastern MT/WY later tonight in response 

to upper/thermal ridge building into the region. 250-750J/kg mean 

SBCAPE develops along the surface trough this afternoon, but with 

increasing MLCIN north of boundary. However, along the surface 

trough as it interacts with the Black Hills, convective initiation

(per CAMs) should occur early this afternoon and then quickly 

wane early this evening with loss of solar insolation. Bulk shear 

is weak, so organized thunderstorms unlikely (CAM wind fields 

signal outflow dominated storms), but gusty winds possible given 

forecast soundings. Temperatures will be near guidance.



Saturday, warm front surges through CWA as upper/thermal ridge 

continues to build. Weak trough slips into the CWA later Sunday 

as upper ridge moves eastward in response to upper trough 

deepening over the northwest CONUS. A few thunderstorms should 

develop along it with deep boundary layer mixing potentially 

supporting a marginal risk of damaging wind gusts near the MT/ND 

border. Boundary stalls Monday/Tuesday as southwest flow aloft 

funnels a couple of weak shortwaves through the northern Plains 

with some convection, mainly during peak heating. Strong signal 

for near record/record temperatures Sunday/Monday per 90th+ 

percentile EFI MaxT and NBM probabilities of 90F+ 70-100% on the 

western SD plains. Upper trough then becomes more dominant over 

central North America resulting in unsettled weather for the rest 

of the week along with a cooling trend. NBM QPF amounts Wednesday 

through Friday show 30-50% chance of 0.25-0.50" across the 

northern half of the CWA, but convective elements will modulate 

localized amounts.



&&



.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)

Issued At 449 AM MDT Fri May 9 2025



Scattered storms with brief/local MVFR conditions/gusty erratic 

winds will develop this afternoon/early this evening over the 

Black Hills and adjacent plains of northeastern WY/southwestern 

SD. Otherwise, VFR conditions are expected through the forecast 

period.



&&



.FIRE WEATHER...

Issued At 159 AM MDT Fri May 9 2025



Unseasonably warm temperatures will blossom Saturday, persisting 

through Tuesday. Minimum relative humidities in the teens are 

expected. Deep boundary layer mixing will bring gusty southerly 

winds at times, especially Sunday/Monday east of the Black Hills. 

Thus, elevated fire weather conditions foreseen with Fire Weather 

Watches or Red Flag Warnings dependent on fuel status status 

updates from land managers.



&&



.UNR WATCHES/WARNINGS/ADVISORIES...

SD...None.

WY...None.

&&



$$



DISCUSSION/KEY MESSAGES...Helgeson

AVIATION...Helgeson

FIRE WEATHER...Helgeson