Winner, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

648
FXUS63 KUNR 141923
AFDUNR

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

.KEY MESSAGES...

- Strong thunderstorms possible across our east today, with heavy
  rain expected in spots.
- Windy with continued rain chances anticipated tomorrow.
- Unsettled pattern persists into next week, with anomalously wet
  conditions possible.

&&

.DISCUSSION...(This Evening Through Wednesday)
Issued at 123 PM MDT Wed May 14 2025

Water vapor imagery at this hour depicts a strengthening upper low
over the Intermountain West. This trough is becoming increasingly
negatively tilted with time as an associated upper jet near its base
emerges onto the central Plains. As the trough pivots, it is
supporting CI in the vicinity of a low-level baroclinic zone across
western/central SD. Existing convection is largely on the cool side
of this boundary, implying it is elevated. MUCAPE of 1-2 kJ/kg and
effective bulk shear magnitudes approaching 40 kt are supporting
some organization of this convection, with modest, transient updraft
rotation and radar signatures supporting sub-severe hail.
Significant temperature gradient is evident across the area owing to
the aforementioned baroclinic zone, with 40s/50s over northeastern
WY and lower 80s over south central SD.

Lobe of enhanced Q-vector convergence will pivot from northern CO to
the northern High Plains this afternoon and evening. Deep forcing
for ascent coupled with ample instability and 150-200% of normal
PWATs should prompt widespread CI. MLCAPE of 1-2 kJ/kg could support
robust updrafts, but minimal overlap with appreciable 0-6 km bulk
shear magnitudes will likely limit storm organization outside of
local, transient effects that could augment low-level shear. This is
consistent with WoFS runs so far this afternoon, which tend to show
compact 2-5 km UH tracks and fairly low machine learning
probabilities of severe hazards. Even if storms can temporarily get
organized, storm motion will generally fall along the axis of the
baroclinic zone, promoting upscale growth and training versus
discrete evolution. Best potential for severe would be around the
time of the evening transition/post-sunset, when forecast low-level
hodographs lengthen and broaden across south central SD. Welcome
moderate to heavy rainfall may turn out to be the primary outcome
from this activity, with 12z HREF showing 2"+ of QPF likely (70% or
greater probabilities) over much of our eastern tier of counties
this evening through tomorrow morning and 3-4"+ serving as a
reasonable wettest case (90th-95th percentile).

As the upper wave pivots over the region tomorrow, the associated
surface low deepens rapidly over the eastern Dakotas, leading to a
tightening pressure gradient across much of our area. By daybreak or
shortly thereafter, boundary layer winds will likely exceed 30 kt
for most of western SD, with further increases probable through the
day. The upper wave transitions to an elongated west-east oriented
trof that gradually strengthens and closes over the Upper Midwest by
tomorrow night, which should prolong potential for windy conditions
and lingering shower activity. HREF probabilities of wind gusts
exceeding 50 mph increase and expand late morning through the
afternoon, with advisory-level gusts becoming likely (70%+
probabilities) by mid-afternoon. Probabilities of 60+ mph gusts are
low for now in the HREF; however, I suspect the HREF is under doing
the gust potential somewhat given forecast soundings. Have opted
to maintain the current High Wind Watch and expand it to include
Tripp County, with the expectation that some of the area may be
upgraded to a warning this evening or overnight. The cyclone
slowly departs on Friday, but gusty winds may continue through
early in the day as a relatively tight pressure gradient persists.

Shortwave ridging, or at least zonal flow, looks to briefly return
early in the weekend before a deep, broad trof takes shape over much
of the western CONUS late weekend into early next week. This will
favor above normal precipitation and near to below normal
temperatures from Sunday through the first half of the week. EFI and
GEFS M-Climate suggest precipitation early next week could be
anomalous, with 6-hr, 12-hr, 24-hr, 48-hr, and 72-hr QPF amounts
from next Monday through next Wednesday all approaching GEFS
reforecast maxima--welcome precipitation as the region continues to
experience abnormally dry to extreme drought conditions.

&&

.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>014-025-031-032-043-044-046-047-049-072-
     073-077-078.
WY...None.
&&

$$

DISCUSSION/KEY MESSAGES...Sherburn
AVIATION...Schultz