690
FXUS63 KFSD 220320
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1020 PM CDT Tue May 21 2024

.KEY MESSAGES...

- The severe risk is quickly waning across the area, though
  there will be a narrow window through 4 pm that could result
  in the potential for large hail and gusty thunderstorm winds
  over portions of northwestern IA and southwestern MN.

- Strong north to northwest winds will continue to develop through
  the afternoon and evening. Some potential for gusts to 40 to
  50 mph through the I-29 corridor and then across Southwest
  Minnesota.

- After a brief break from rain, additional thunderstorms are
  expected Thursday night through Friday. Isolated strong to
  severe thunderstorms are possible.

&&

.DISCUSSION...
Issued at 305 PM CDT Tue May 21 2024

Current SPC mesoanalysis indicates a surface low centered over far
eastern NE and western IA as of late this afternoon. An area of
showers and thunderstorms align with this low through northwest IA,
with a stronger line of storms oriented from north to south along
the extreme southeastern portions of our CWA in association with
convergence along the surface low axis. Mesoanalysis indicates
MUCAPE of 1000-2000 J/KG residing from parcels lifting from around 2-
3 kft AGL, with effective shear of 35 to 50 kts over that area.
Although we have had no severe reports with this activity as of yet,
these parameters would suggest a continued possibility of hail to the
size of ping pong balls and thunderstorm wind gusts of up to 65
mph. In addition, with low LCLs and surface vorticity maximized
along this line, cannot rule out a isolated tornado - though
other better tornado parameters reside well east of our CWA. All
that being said, this line of convection is expected to exit
the area over the next hour or so as the surface low pushes off
to the east - so the severe threat is expected to be short
lived.

On the back side of the low - where the tighter surface pressure
gradient (SPG)resides - winds have been gusting around 40 mph
through the mid afternoon. May see these winds pick up a notch more
through the late afternoon/early evening as the low moves east and
the tighter SPG slides over the area. In light of that, will keep
the existing Wind Advisory going over portions of our area into late
this evening. With the surface moving into eastern IA/eastern MN
between 00Z-01Z, showers and thunderstorms will completely move out
of our area by then. With cold air advection on the backside of the
system, it will be a cooler night with lows in the mid to upper 40s.

On Wednesday the surface low tracks from the Upper Mississippi
Valley into south central Canada, leading to a dry day over our
area. There will be enough of surface pressure gradient remaining
that breezy easterly winds will persist through the northeastern
portions of the CWA. Temperatures will be near normal - in the upper
60s to lower 70s.

After the one quiet day on Wednesday, active weather returns to the
area on Thursday as another surface low develops through the Central
and Northern Plains while an upper level low tracks out of the
Northern Rockies. This will bring our next chance of showers and
thunderstorms, focused on Thursday night into early on Friday. Still
some uncertainty regarding any severe potential for that period,
though convective parameters would suggest at least some possibility
- as evidenced by SPC Day 3 Marginal outlook for our area. Latest
ensembles suggest around a 70% probability of receiving at least a
quarter of an inch of rainfall with this system.

The active pattern looks to continue into the beginning of next
week, with shower/thunderstorms chances focused on Saturday night
and Sunday night. Temperatures remain at or just above normal
through the period.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1018 PM CDT Tue May 21 2024

VFR conditions are expected through the overnight hours as winds
continue to quickly weaken.

Some mid-high level clouds will drift into areas west of the
James River at times, though this activity should dissipate for
Wednesday.

VFR conditions and light winds continue Wednesday with a
reasonable risk for afternoon CU developing.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...JM
AVIATION...Dux