669
FXUS63 KFSD 121937
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
237 PM CDT Sat Jul 12 2025

.KEY MESSAGES...

- Wildfire smoke continues to move into the region this
  afternoon. Reductions in visibility and air quality are
  expected in the smoke before it exits the area by tomorrow
  morning. Unusually sensitive individuals should take the
  necessary safety precautions.

- Heat and humidity build back in for Sunday through Tuesday.
  Cooler temperatures return for the middle and end of next
  week.

- A low (~20% chance) thunderstorm risk for Sunday afternoon,
  then a higher threat for Tuesday and Tuesday night - with some
  threat of severe storms and heavy rainfall possible during
  that period.

&&

.DISCUSSION...
Issued at 236 PM CDT Sat Jul 12 2025

High pressure continues to push through the area this afternoon.
High temperatures have warmed to the 70s while winds remain
marginally breezy out of the northwest. While a pleasant rest of the
afternoon is expected, smoke from wildfires in Canada continues to
push into the area. Visibilities down to 9 to 6 miles have been
reported and will sweep through locations along and north of I-90
and generally east of the James River through the late afternoon,
evening, and overnight hours. Should see the smoke finally exit the
area come tomorrow morning. Lows will fall to the upper 50s and 60s
overnight.

Sunday will be a hot day as 850 mb temperatures warm to the upper
teens to low 20s aloft. Mixing these temperatures to the surface
will result in highs spanning into the 80s and 90s, warmest west of
the James River. A surface trough and associated boundary will be
sliding through the forecast area throughout the day which continues
to show increasing chances of developing convection Sunday
afternoon. While lapse rates will not be that impressive, tall
skinny CAPE profiles will be present with a magnitude of about 1,500
J/kg. Shear profiles will support about 30 knots of effective shear.
Forcing will be very weak given large scale subsidence prevailing on
the backside of a departing shortwave trough. However, latest
guidance is in decent agreement in a second, weak shortwave trough
passing through behind the previously mentioned wave. Thus,
convection looks to initiate in an uncapped environment. Questions
remain regarding the overall coverage of storms but looks like the
large scale subsidence should hold storms below severe limits. That
said, small hail and gusty winds remain possible. Any chance for
rain will push east of the area during the evening hours, leaving
dry conditions for the overnight hours. Lows will fall to the 60s
overnight.

Zonal flow looks to take over for the first half of next week. Weak
shortwave troughs look to pass through the upper level flow,
bringing multiple chances for rain with them. The first wave looks
to come on Monday but the surface fronts placed well north and west
of the forecast area, dry conditions are likely for the day.
Continued warm air advection (WAA) aloft will continue to push 850
mb temperatures up to the low to mid 20s. This will yield highs up
to the upper 80s and 90s, warmest again west of the James River.
Some locations west of the James could see highs near 100F. Heat
indices will also rise into the 90s across the are, making for a hot
and humid day.

The main chance for rain will come on Tuesday as the previously
mentioned airmass slides southward, pushing a cold front into the
forecast area. This front looks to spark convection along it as
ample instability will be in place. Severe storm potential is a bit
questionable at this time as medium range guidance shows little to
no vertical shear. However, machine learning guidance does show
about a 15% chance for strong to severe storms. The other aspect to
the storms is the potential for heavy rain. Precipitable water
(PWAT) values look to rise to the 90th percentile of climatology per
the NAEFS ensemble. Mean flow will also be parallel to the boundary
as well, promoting the potential for training storm develop. Latest
machine learning probabilities also support this heavy rain
potential as it shows a 5 to 15% chance for excessive rainfall. Rain
chances will continue through Wednesday as the front dives south of
the forecast area. There could be additional showers and
thunderstorms though instability looks to be low in the post frontal
environment so storms may be a bit harder to come by. Temperatures
for Tuesday and Wednesday will be a bit cooler, falling to the 80s
to up to about 90F on Tuesday and then the 70s and 80s on Wednesday.

The end of next week looks to have continued rain chances as weak
shortwaves continue to push into the area aloft. However, medium
range guidance shows increasing variance regarding the evolution of
these waves. Thus, have left model blended PoPs in place. Aside from
rain chances, temperatures look to remain near to below average in
the 70s and 80s Thursday and Friday before warming back to the 80s
on Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1220 PM CDT Sat Jul 12 2025

Mainly VFR conditions are expected for the TAF period. A CU field it
visible on latest satellite imagery east of I-29 based around
4,000ft. Wildfire smoke is also present aloft and will be at the
surface later this afternoon. The smoke is already present at the
surface in northern South Dakota and will continue to track
southeastwards into the area during the afternoon hours. Locations
along and north of a KHON to KFSD to KMJQ line will see some
visibility reductions from the smoke. The smoke will persist through
the evening hours before retreating to the northeast. Winds will go
light and variable tonight before slightly restrengthening out of
the southwest tomorrow morning. A front will be entering the area
from the northwest to end the TAF period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...Meyers