799 
FXUS63 KUNR 181124
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
524 AM MDT Fri Jul 18 2025

.KEY MESSAGES...

- Daily chance for at least isolated thunderstorms, some of which
  may be strong to severe, are expected into early next week
- Expect more seasonable temperatures through next week with 
  above normal temperatures likely at times

&&

.DISCUSSION...(Today Through Thursday)
Issued at 149 AM MDT Fri Jul 18 2025

07z surface analysis had weak low over northeastern WY with 
trough into southern ND. Water vapour loop had distinct shortwave 
trough zipping across western ND/eastern MT. Surface trough is 
focusing modest 30kt low level jet (KUDX VWP) for elevated 
convection per regional radar loops, tapping into 1-2KJ/kg 
MUCAPE/50-60kt effective shear. Starting to see outflow on our 
radar courtesy of southeast MT/northwest SD convection. 
Ingredients in place for isolated strong/severe storms in the form
of elevated supercells. Will continue to monitor overnight, but 
best convection should be east of the CWA by 12z. Elsewhere, 
stratus has developed over south-central SD. Concern this forecast
revolves around convection chances.

Today/tonight, outflow reinforced surface trough slips into NE as
subsidence develops behind shortwave trough per shortwave ridge 
this afternoon. Trough wraps back north into northeast WY late as 
well as hanging out near south-central SD. This is where ~1KJ/kg 
SBCAPE develops late with 25-35kt 0-6km bulk shear and weakest 
SBCIN. Could see isolated strong/severe storms as a result where 
SPC Day 1 marginal risk has been shunted. Tonight, next shortwave 
moves through with generally benign elevated convection expected 
to move across the CWA overnight. Temperatures should be near 
guidance.

Saturday, new surface low develops over northeast WY along 
surface trough as weak shortwave moves through during peak 
heating. Richer moisture will be available per sustained 
southeasterly upslope flow pushing buoyancy to 1-2KJ/kg SBCAPE 
with 25-35kt 0-6km bulk shear. Given SBCIN, convection should 
focus on surface trough/terrain interaction for isolated 
strong/severe thunderstorms where SPC Day 2 marginal risk is 
placed. Subjectively, looks like a good setup for severe weather 
if cap can be overcome. Temperatures will be near guidance.

Sunday, rinse and repeat but with warmer temperatures and a 
distinct tilt toward some 90s on the northeastern WY/southwestern 
SD plains. Zonal flow next week still looks probable with a series
of shortwaves parading across the US/Canadian border resulting in
summery temperatures and daily chances for thunderstorms.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Saturday Morning)
Issued At 520 AM MDT Fri Jul 18 2025

Behind a convective outflow boundary, areas of IFR conditions are
expected this morning, most concentrated over the Black Hills and
over south-central SD. VFR conditions will return this afternoon 
with isolated/scattered TSRA in/near Black Hills later this 
afternoon and then areawide tonight as a cluster of shra/TS with 
local MVFR conditions moves from west to east across the area. IFR
stratus is likely after 06z Saturday over south-central SD.

&&

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

$$

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