297
FXUS63 KFSD 152323
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
623 PM CDT Sun Sep 15 2024

.KEY MESSAGES...

- Temperatures remain above normal through at least the middle
  of this week. Nighttime lows show greater departures above
  normal (10- 15F) than daytime highs (5-10F) due to anomalously
  high low level moisture/dew points.

- Greater chance for rain (40-70+%) returns mid-week, mainly
  focused west of I-29 Tuesday night to early Wednesday.
  Moderate (40- 50%) probability of rainfall exceeding 0.25",
  but low (10-30%) probability of exceeding 0.50".

- Moderate chances (40-60%) for showers/storms late week,
  currently focused Thursday night-Saturday night, though exact
  timing and location details are still uncertain.

&&

.DISCUSSION...
Issued at 156 PM CDT Sun Sep 15 2024

Isolated showers and storms remain possible this afternoon with weak
elevated instability and a shearing weak wave aloft. Latest trends
are seeing the ACCAS dissipate, so the chances seem to be dwindling.
South to southwest flow aloft remains in place through tonight, with
the faster flow to the west. Will once again see a small chance for
showers and thunderstorms in central SD tonight but severe weather
looks unlikely. With a bit better mid level wave coming in later
tonight into Monday the chances will linger mainly west of I-29
through the day Monday. Much above normal temperatures continue with
lows in the mid and upper 60s and highs in the mid 80s.

Monday late afternoon and evening a weak wave will drift north into
central SD and should allow a few thunderstorms to develop. There is
marginal instability and weak shear so if something can develop
an isolated severe storm will be possible.

More of the same on Tuesday and Tuesday night as the main faster
upper level flow remains west of the area and just a few weak waves
drift northeast which could interact with any weak elevated
instability to produce isolated showers and storms, with a very low
chance for severe weather. Highs on Tuesday will be in the 80s with
lows Tuesday night into Wednesday in the 60s.

Wednesday into Saturday the models are in fairly good agreement in
deepening an upper level low over the central and northern Rockies
and swinging it north northeast. This continues to leave the area in
southwest flow aloft with periodic waves ejecting ahead of the main
low. Still some questions marks with the main upper level support so
far northwest. Still looks like periodic chances for showers and
thunderstorms during this time, just a continuation of relatively
low confidence on coverage and timing.

Some larger differences begin to appear Sunday into Monday, with the
GFS much more aggressive in swinging this stronger low to the north
eastward, which will advect colder air into the region. The Canadian
and ECMWF weaken this low and develop a new low across the Plains
which would keep warmer air in place and better chances for rain and
thunderstorms. No real confidence one direction or the other.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 623 PM CDT Sun Sep 15 2024

VFR conditions are expected for the TAF period. Elevated
southeasterly winds this evening will persist through the overnight
hours with speeds up to 5-10 knots. Showers and thunderstorms have
developed across the front range of the Rocky Mountains this
evening. The storms will track northeastwards into the overnight
hours. They could push into areas along and east of the Missouri
River Valley but confidence is low (<30% chance) in this scenario
occurring. Will continue to monitor trends. Otherwise, breezy
southerly winds will return tomorrow with gusts up to 15-30 knots
expected. The strongest gusts will occur west of I-29.

&&

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

&&

$$

DISCUSSION...08
AVIATION...Meyers