158
FXUS63 KUNR 201128
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
528 AM MDT Sun Apr 20 2025

.KEY MESSAGES...

- Elevated fire weather conditions likely across the western SD
  plains this afternoon and Monday

- Showers and a few thunderstorms possible Monday, some of the
  stronger storms may be capable of small (sub-severe) hail and
  gusty winds

- Active pattern will bring occasional precipitation chances
  through next week

&&

.DISCUSSION...(Today Through Saturday)
Issued at 239 AM MDT Sun Apr 20 2025

Current WV imagery and upper air analysis depicts upper level
trof axis extending from the Northern Plains into NM. A well
defined upper low spins over the TX panhandle with convection
arcing across the Southern Plains from Kansas to the Mexican
border. Closer to home, a filament of dry air extends into the
CWA, resulting in clear skies over western SD and northeastern WY.
Temperatures are in the 30s to 40s across the plains and in the
20s across the Black Hills.

Upper level shortwave and attendant sfc trof will move through
the CWA this afternoon. Steep lapse rates and weak buoyancy may be
enough to trigger a few gusty showers and maybe a rumble of
thunder as the trof passes through, however moisture will be
limited which may prevent any deeper convection from occurring.
Ahead of the trough, RHs across western SD will plummet into the
teens to 20s, with RHs as low as 15% possible. Widespread elevated
fire wx conditions are likely, however the gustiest winds will be
behind the sfc trof, and not collocated with the lowest RHs.
Elevated fire wx is also possible across south central SD Monday
afternoon as RHs dip below 20% and southerly winds pick up ahead
of a front.

Better chances for precip come on Monday afternoon and evening as
another shortwave and attendant front crosses the region. This
system will be carrying a little more mid-level moisture, sourced
from the Pacific. Cooler air aloft will support steep lapse rates
as sfc temps climb into the 50s to 60s across northeastern WY and
into the 70s across the western SD plains by Monday afternoon.
Deterministic NAM and HRRR runs depict 250-500 J/kg MU CAPE and
30- 40kt bulk shear. Moisture is still going to be a limiting
factor for deeper convection, however. Any stronger storms that do
manage to get going may be capable of small (sub-severe) hail and
gusty winds. The Black Hills could see a rain/snow mix Monday
evening into Monday night as colder air filters into the region;
however not anticipating any accumulations.

Unsettled and progressive upper level pattern will continue
through the week with periodic disturbances rippling across the
southwest flow. These systems will bring occasional chances for
light precip to the region. However, deterministic models express
a lot of model-to-model and even run-to-run variability on
specifics of timing, track, and intensity of any individual
disturbances later this week.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Monday Morning)
Issued At 528 AM MDT Sun Apr 20 2025

VFR conditions are expected across most of the area today into
tonight. A weak disturbance will move across northeast WY and into
far western SD later this morning and afternoon, bringing
isolated to scattered rain showers. Some areas of MVFR conditions
are possible across northeast WY into the Black Hills during the
midday and afternoon hours. Showers will dissipate this evening.

&&

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

$$

DISCUSSION/KEY MESSAGES...Wong
AVIATION...26