FXUS63 KFSD 182342
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
642 PM CDT Mon May 18 2026

.KEY MESSAGES...

- Showers and isolated thunderstorms return to the area this 
  afternoon this evening into tonight. 

- A few storms along and southeast of a Wayne to Sheldon to
  Windom line may be strong to severe late this afternoon into
  this evening. The main threat would be hail to half dollar
  size but storms this strong should remain very isolated and
  likely closer to near and east of Highway 60.

- Areas of frost or freeze will be possible on Wednesday 
  morning, with the better chances north of I-90.

- Cool conditions prevail this week. Dry weather expected mid 
  week. Another round of storms is possible Thursday through 
  Friday.

&&

.DISCUSSION...
Issued at 1258 PM CDT Mon May 18 2026

Early this afternoon the surface to 925 mb front was across southern 
NE into southern IA. Given the marginal strength of the incoming 
wave, this boundary should not lift far enough north and west 
by late afternoon to get into the area. This should limit any 
wind and tornado threats and keep them off to the southeast. 
However, some elevated hailers will remain possible across 
mainly northwest IA as elevated CAPE values ramp up to about 
1000-1500 J/KG and deep layer shear is a fairly strong, 
unidirectional 40-50 knots. This would be lifting a parcel from 
above the stratus layer, which would likely be in about the 
800-750mb layer. The better chances will be from about 5 pm to 9
pm.

After this wave pushes the remaining instability out of the area 
this evening, dry and cool conditions are expected for Tuesday and 
Wednesday. The only concerns on these two days will be the potential 
for frost and freeze conditions, mostly north of I-90, as surface 
high pressure is in place. Another weaker wave moves through the 
area on Wednesday but for now this appears to bring mainly mid level 
cloud cover.

The next better chance for showers and thunderstorms will come 
Thursday night into Friday night. At this time severe weather looks 
to remain isolated as model instability fields are hinting at 1000 
J/kg CAPE or less for the most part.

Once this wave passes a warming trend should move in as flat ridging 
aloft develops ahead of a deepening low pressure in the Northern 
Rockies. Saturday should be mild, likely in the 70s, while Sunday 
sees the better chance to warm into the 80s.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 636 PM CDT Mon May 18 2026

Mainly IFR to LIFR ceiling and vsbys continue this TAF period.
Taking a look at satellite imagery, we're continuing to see
scattered showers and thunderstorms develop east of I-29. While
these conditions will likely persist into the evening, should 
see things transition to mainly MVFR to IFR cigs as the lower 
ceilings continues to produce pockets of drizzle. Otherwise, 
breezy northwesterly winds will continue into the overnight to
end the TAF period.

&&

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

&&

$$

DISCUSSION...08
AVIATION...05