Swan Lake, South Dakota Weather Forecast Discussion

512
FXUS63 KFSD 221120
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
620 AM CDT Mon Sep 22 2025
.KEY MESSAGES...
- Areas of patchy fog will continue through mid-morning. With
  rapid changes in visibility possible over short distances,
  make sure to additional time when making those morning
  commutes.
- Additional chances for showers and thunderstorms are expected
  this afternoon and evening mainly south of I-90. A few storms
  may become severe with up to ping-pong ball (1.5") size hail
  and damaging wind gusts up to 60 mph being the primary threats.
- A pattern shift will lead to much quieter conditions and
  temperatures near to just above normal with highs mainly in
  the 70s to 80s.
&&
.DISCUSSION...
Issued at 258 AM CDT Mon Sep 22 2025
Another warm day ahead! Taking a look across the area, a few spotty
showers and thundershowers continue early this morning across the I-
90 corridor mostly in response to lingering lift associated with a
passing wave and a nocturnal 925mb LLJ. While this spotty activity
could fester through about daybreak, should see things gradually
diminish as the LLJ weakens. From here, could see a few areas of
patchy fog develop across the area this morning as surface winds
become light and variable. While rapid chances to visibility
will be possible over short distances, should things gradually
clear up between daybreak to mid-morning (9 am). Looking into
the rest of the day, quieter conditions will temporarily return
from the late morning to early afternoon as temperatures peak in
the 70s to low 80s for the day. However, our focus will shift
towards our precipitation chances (30%-50%) from the early
afternoon onwards as a shortwave intersects a stationary
boundary south of I-90 triggering showers and thunderstorms.
Looking at the CAMs, there is still some lingering uncertainty as to
where the southeastward progressing boundary sets up once the wave
arrives which has led to two specific camps of solutions. The first
camp (HRRR & RAP13) has convection initializing closer to the I-90
corridor along the front and gradually progressing southwards
through the evening. The second camp (ARW, Fv3, and NAM Nest) has
scattered showers initially developing across the Missouri River
Valley with a developing surface low. However, as this low
intersects the boundary; stronger convection should take off in
northwestern IA and portions of the lower Missouri River Valley then
gradually progresses southeastwards during the evening. While both
camps are feasible solutions, still leaning towards the second camp
of solutions given how things have been trending southwards over the
last few days. Nonetheless, given the 1500-2500 J/km and 20-30 kts
of shear; a few stronger storms remain possible with the main
hazards being up to ping-pong ball sized hail (1.5") and damaging
winds up to 60 mph. With all this in mind, the main timeline for any
stronger activity will likely be between 3 pm to 10 pm. However, if
things can develop further south (closer to highway-20); the window
will narrow considerably to 3pm to 7 pm. From here, should see things
quiet down during the overnight hours as temperatures drop into the
low to upper 50s for lows.
Looking into the midweek onwards, a pattern shift begins to take
shape as the departing long-wave trough is replaced by building
upper-level ridging. With this likely keeping our precipitation
chances at bay for a while, expect temperatures to continue to sit
in the 70s to low 80s through the weekend. With this in mind, this
would be a good time to finish any lingering outdoor projects and/or
plan some outdoor activities so get out an enjoy the beautiful
conditions! Lastly, we`ll have to continue to monitor for fire
weather concerns over the next few weeks as limited moisture and
warm temperatures should begin to dry out our fuels overtime.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 615 AM CDT Mon Sep 22 2025
Mostly VFR with occasional MVFR to IFR vsbys will be possible
this TAF period. Taking a look at satellite imagery, mostly
clear conditions persist with some patchy areas of fog this
morning. Should see any developing fog gradually diminish
shortly after daybreak. From here, shower and thunderstorm
chances will increase this afternoon and evening mainly south of
I-90 leading to occasional MVFR to IFR vsbys. With this in
mind, added in a PROB30 group into KSUX to account for the
increasing probabilities. Otherwise, light easterly to northeasterly
winds will persist for the rest of the TAF period.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
DISCUSSION...05
AVIATION...05

NWS FSD Office Area Forecast Discussion