268
FXUS63 KUNR 222357
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
557 PM MDT Thu May 22 2025

.KEY MESSAGES...

- Band of shra/TS moves across the area tonight/Friday morning
- Upper trough brings moist/cool Memorial Day weekend
- Unsettled weather for most of next week as temperatures moderate

&&

.DISCUSSION...(This Evening Through Thursday)
Issued at 143 PM MDT Thu May 22 2025

19z surface analysis had weak high over the eastern Dakotas with
return flow developing over the CWA. 0.5km visible satellite loop
showed cellular cumulus scattered about. Water vapour loop
depicted shortwave ridge over the northern Plains with shortwave
trough over the northern Rockies and 90kt jet streak nudging the
trough eastward. Main short term forecast concern is evolution of
shortwave trough and then larger upper trough for the holiday
weekend.

Tonight/Friday morning, shortwave trough moves into the northern
plains with well-defined band of 800-700mb theta-e advection on
modest southerly low level jet. <500J/kg MUCAPE becomes available
this evening. Expect a band of shra/TS to develop early this
evening across the southwest, moving northeast overnight and
ending up from K2WX-KICR Friday morning, which is where the
greatest chance (60-90% per SPC HREF) of >0.10" QPF lies.
Temperatures will be near guidance.

Friday afternoon/night, a deeper, partially split upper trough
develops from MT to UT with shortwave ridge over the CWA and moist
easterly component to low level flow. This will support
increasingly dreary weather over the eastern half of the CWA
(stratus/fog) with some sunshine over the west. Diurnal heating
will promote isolated/scattered shra/TS. Temperatures will be near
guidance.

Saturday through Memorial Day, mean upper trough slowly slides
from the Rockies into the plains with sustained southeasterly low
level flow promoting showers/TS at times, especially over the
southern 2/3rds of the CWA where the chance of >0.50" 72-hour QPF
is 60-90% per LREF/NBM with 50% chance of >1.00" over southern SD.
Locally higher amounts likely given upslope flow and potential
for convection. Buoyancy forecast is not conducive to organized
severe thunderstorms. Pattern recognition suggests fog/drizzle
will probably be mixed in. Given time of year, there will likely
dry spells, especially over the northern half the CWA. Temperatures
will be 10-15F below normal.

The rest of next week looks unsettled per moist cyclonic flow.
Temperatures will moderate as thermal ridge edges eastward into the
northern Plains.

&&

.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 555 PM MDT Thu May 22 2025

Scattered storms will cross northeastern WY and western/central
SD late this evening through the overnight hours. MVFR/IFR CIGS
are then expected to develop Friday morning across northwestern to
central SD and also the WY/SD Black Hills.

&&

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

$$

DISCUSSION/KEY MESSAGES...Helgeson
AVIATION...13