077
FXUS63 KFSD 121721
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1221 PM CDT Sat Jul 12 2025

.KEY MESSAGES...

- Dry with below normal temperatures for today. Wildfire smoke
  moves into the region today into this evening, and this could
  reduce visibility and air quality - primarily over the eastern
  portions of the CWA.

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

- A low thunderstorm risk for Sunday afternoon, then a higher
  threat for Tuesday and Tuesday night - with some threat of
  severe storms possible during that period.

&&

.DISCUSSION...
Issued at 317 AM CDT Sat Jul 12 2025

A gorgeous day ahead as surface high pressure builds into the
region. An 850 mb thermal trough (teens C) slides eastward over the
region through the day, and this will mix out to highs in the upper
70s to mid 80s. In addition to the relatively mild temperatures, dew
points mainly in the 50s will result in an even more comfortable
day. The only downside to the day will be the likelihood of Canadian
wildfire smoke drifting into the region, with both the HRRR and RAP
indicating that some of this may reach the surface over the eastern
portions of the CWA by afternoon and evening. Even so, the current
Air Quality forecast would indicate AQ remaining in the moderate
range (level 2 out of 6), so while this will not impact most
individuals those sensitive to smoke should take precautions. By
tonight the low level flow begins to transition to southerly as the
surface ridge shifts into the central Mississippi Valley, though it
will still be a rather pleasant night with lows in the upper 50s to
lower 60s.

A return to much warmer temperatures by Sunday and Monday with
rising upper level heights and a strengthening southerly low level
flow. This will push temperatures back to above normal levels both
days, with highs in the mid 80s to mid 90s. In addition, it will
become increasingly humid as dew points climb back into the 60s to
lower 70s. A surface trough will slide across the area on Sunday
afternoon and evening, and a few of the hi-res models suggest
isolated thunderstorms developing generally from the Interstate 29
corridor and eastward. Do feel that anything will remain very
isolated with the better upper level support remaining to the north
of our area. Although there will be instability present (MLCAPE 2000-
2500 J/KG), bulk shear is only around 25 kts with mid level lapse
rates only around 5-6 C/KM, so the severe threat will be low.

Latest guidance would suggest that Monday into Monday night will
remain primarily dry with convection focused to our north in the
vicinity of a stalled frontal boundary draped across northern SD
into central MN. This begins to change by Tuesday afternoon and
Tuesday night as the frontal boundary finally drops southward into
our area and a series of upper level shortwaves move through the
region. Although a little early for specifics, have to keep in mind
the potential for at least some severe threat with plenty of
instability in place - although bulk shear appears to be on the lower
side at this point. That could change over the next few days so will
bear watching. Of note, as mentioned in the previous discussion,
machine learning guidance continues to indicate a 10-15% probability
of severe weather in our area during that period.

Behind this system, below normal temperatures work back into the
area for the mid and end of next week with highs in the 70s to near
80 and lows in the 50s to lower 60s. Precipitation chances through
this period will be focused more so on Wednesday into early Thursday
as an upper level trough swings through the region, then trending
drier for the end of next week.

&&

.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...JM
AVIATION...Meyers