Shelby, South Dakota Weather Forecast Discussion

447
FXUS63 KFSD 211127
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
627 AM CDT Sun Sep 21 2025
.KEY MESSAGES...
- Morning showers and a few thunderstorms will be possible, as
  lingering fog may drop visibilities below 1 mile in some
  locations.
- Isolated to scattered thunderstorm development will be
  possible after 3-4pm this afternoon. Marginal risks for severe
  storms will be possible, with half dollar size hail and 50
  mph wind the greatest risks into the evening.
- Lingering thunderstorm risks on Monday afternoon and evening,
  through trends continue to push risks further south.
- The remainder of the week continues to appear dry with
  temperatures near to above normal into next weekend.
&&
.DISCUSSION...
Issued at 220 AM CDT Sun Sep 21 2025
THIS MORNING: Considerable cirrus overspreading the area remains
thin enough in spots to allow sufficient radiational cooling
fog to develop. While this fog is not all that widespread, we
have seen localized visibilities less than 1 mile in a few
areas. Fog will persist through daybreak, but will likely stay
patchy enough to avoid any advisories. Will continue to monitor.
Elsewhere, VWP showing sharp increases in 850 mph winds from
the Thedford radar this morning approaching 30-35 knots. These
wind increases have resulted in a corridor of mid-lvl clouds
further north across south central South Dakota this morning.
Model guidance continues to show these low-lvl wind increases
spreading eastward over the Tri-State area, with moisture
convergence likely leading to a few showers or even
thunderstorms by daybreak.
TODAY:Scattered showers and a few thunderstorms may continue to move
east into Minnesota this morning as convergence and the nose of the
LLJ moves across the CWA.  This increase in cloud cover may stunt
the upward diurnal trend in temperatures slightly, but by mid-day we
should see ample sunshine in most locations.  The main concern this
afternoon will be redevelopment of isolated to scattered
thunderstorms along a stalled frontal boundary splitting the CWA by
mid-afternoon.  Models continue to show upwards of 1000-1500 J/KG
MLCAPE values forming by mid-afternoon along and south of this
boundary.  By mid-late afternoon increased focus for convection
should develop from Southwest Minnesota southwest along the
aforementioned boundary into south central South Dakota. Storms
will develop initially on the northeastern portions of the CWA
where slightly stronger lift from an approaching mid-lvl trough
arrives. The increase in low-lvl flow towards 00Z should result
in a modest bump in effective shear (AOA 30 knots), with storm
mode mostly multi- cells with isolated supercell structures.
Soundings along and ahead of the boundary support modest mid-lvl
lapse rates near 6.5-7 C/km, with a slight dry air intrusion.
This would support occasional half dollar hail and very isolated
50-60 mph wind gust potential into the evening. While the
tornado risk is very low, some parameters do suggest a very
isolated risk in SW Minnesota and far northern Iowa early in the
evening as LL winds increase.
THIS EVENING AND TONIGHT:  The majority of storms are favored to
stay along or especially east of I-29, but an isolated storm could
build back westward along the boundary towards the MO River.  While
the severe weather risk will wane towards 10pm, the lingering low-
lvl jet axis may keep storm percolating into the overnight hours.
While widespread heavy rain isn`t expected, HREF PMM guidance
suggests that potential for isolated 1-2"+ totals are possible,
especially in southwestern Minnesota and far northern Iowa. With low-
lvl flow turning weak after midnight, would not be surprised to
see stratus or more likely fog develop over eastern South
Dakota and western Minnesota. HREF probabilities of 

NWS FSD Office Area Forecast Discussion