546
FXUS63 KFSD 060600
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
100 AM CDT Thu Aug 6 2026

.KEY MESSAGES...

- Areas of fog are likely early this morning mainly over
  northwest Iowa and nearby portions of northeast Nebraska and
  southeast South Dakota. Fog lifts by the mid-morning hours.

- Dense fog is likely near and southeast of a Sioux City to
  Spencer, IA line through 10 am. Be prepared for changing
  visibility on your morning commute in these areas.

- Temperature will continue to trend near to above normal into
  the weekend with highs mainly in the 80s to low 90s.

- Besides some smaller periodic rain chances (20% or less),
  mostly dry conditions are expected through Sunday.

&&

.UPDATE...
Issued at 929 PM CDT Wed Aug 5 2026

No major changes to the forecast for tonight and
tomorrow. The main concern into tomorrow morning will be patchy to
areas of fog that look to develop mainly over northwest Iowa, far
northeast Nebraska, and adjacent areas of far southeastern South
Dakota. Some dense fog is likely, with 05.18Z REFS and 05.12Z HREF
probabilities of less than a quarter mile visibility around 40-60%,
highest near and southeast of a Sioux City to Storm Lake line.
Uncertainty remains on how widespread any dense fog would be, so
current plan is to hold off on issuing any headlines at this time.
Still be prepared to take extra precautions while heading out on the
roads during the Thursday morning commute. Fog looks to form by 1-3
am tonight and then erode by the mid-morning hours tomorrow.
Cooler than normal temperatures continue tonight, though it
won`t be nearly as cool as last night with lows by Thursday
morning mainly in the 50s, warmest northwest and gradually
cooler with southeastward extent.

High temperatures will continue to warm into the day on Thursday as
southerly flow increases and also brings in higher dew points to the
area. Still won`t be that humid, but dew points in the 60s west of I-
29 could push the heat index slightly above the air temperature
tomorrow afternoon. Speaking of air temperatures, look for highs to
range from the middle 80s to around 90 near and west of the James
River, with mainly lower 80s elsewhere. Instability looks to surge
into areas near and west of the James River tomorrow afternoon ahead
of a boundary that will push towards central South Dakota. Soundings
show a stout cap in place, so thunderstorms are unlikely (less than
15% chance). IF a storm can break the cap in the late afternoon as
shown in the typically aggressive HiResW-FV3 model, then severe
weather will be a possibility in south-central South Dakota
where the Storm Prediction Center currently depicts a Marginal
(Level 1 of 5) Risk. Main severe weather hazards in the very low
chance a storm develops will be wind gusts to 65 mph and hail
to the size of ping pong balls.

&&

.DISCUSSION...
Issued at 137 PM CDT Wed Aug 5 2026

Today will be mostly sunny and quiet under high pressure with light
winds and highs in the upper 70s to low 80s. Northwest flow aloft
will bring smoke into the region from wildfires out west. The smoke
is expected to remain mostly aloft and currently throughout our CWA
the air quality is good. For more on air quality and to get an air
quality forecast for your location please see AirNow.gov

Patchy valley fog is possible early Thursday morning as winds
become light to calm. Fog is most likely east of I-29 over
northwest Iowa. Any fog that forms should burn off by mid-
morning. As the high pressure moves off to the east this
afternoon and evening winds will become southerly. At the same
time from the west an upper shortwave will approach the region,
strengthening the LLJ. Overnight winds will begin to increase
from the west to the east. During the day Thursday good mixing
up through the 850 mb level will bring down stronger gusts of 20
to 30 mph for much of the region. Portions of northwest Iowa
will remain lighter at 15 to 20 mph gusts. Conditions are
expected to be dry and warmer thanks to modest WAA. Highs will
range from the low to upper 80s with warmest conditions over
central South Dakota.

Thursday night another subtle upper wave will pivot over the region
bringing chances for showers and thunderstorms. There are a few
trends we will need to monitor over the next 24 to 36 hours. A
narrow band of modest moisture return looks to set up over
central South Dakota, but areas to the east look to remain
fairly dry. Moderate surface based instability of around 1000
J/kg of CAPE will build through Thursday afternoon over central
South Dakota. However, as you move east there is an increasingly
strong cap in place. Instability above the cap is lacking, so
elevated convection would struggle to initiate. So while an
isolated strong to severe storm is possible over central South
Dakota, confidence in any strong storms making it farther east
than US Highway 281 is low. If storms should form it would
between roughly 6 pm and midnight.

Friday sees the return of higher dew points in the upper 60s to low
70s. With highs in the 70s to 80s it will be a bit of a muggy day. A
series of subtle waves will keep low PoPs in the forecast for much
of the day. A more defined wave pivots through Friday evening into
Saturday morning bringing chances for more organized convection,
mainly east of I-29. Periodic storm chances continue through the
rest of the weekend and into the beginning of next week. However,
confidence in timing, coverage, and severity of storms is low as
this is the point where mid-range guidance begins to diverge.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1255 AM CDT Thu Aug 6 2026

Fog is likely to develop over northwest Iowa and adjacent areas
of far northeast Nebraska and far southeast South Dakota early this
morning. Dense fog is likely to develop in spots as well, mainly
near and southeast of a KSUX to KSPW line. Not enough confidence to
include VLIFR conditions at KSUX at this time, but trends will be
monitored. Fog should lift by mid-morning; however, lingering MVFR
stratus may continue through about noon.

Very low (<15%) chance of a thunderstorm near and south of the K9V9
area this afternoon and early evening. Outside of that area,
thunderstorms are not expected through the period. Southerly winds
will increase through the day on Thursday, gusting up to 25 kts this
afternoon in southeastern and south-central South Dakota into the
higher elevations of the Buffalo Ridge in southwest Minnesota. Winds
will be a bit lighter into northwest Iowa and nearby areas.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...Dense Fog Advisory until 10 AM CDT this morning for IAZ014-021-
     022-031-032.
NE...None.

&&

$$

UPDATE...Samet
DISCUSSION...AJP
AVIATION...Samet