809
FXUS63 KFSD 151139
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
639 AM CDT Tue Sep 15 2026

.KEY MESSAGES...

- Patchy areas of locally dense fog should continue to dissipate
  closer as surface winds strengthen.

- A few spotty showers will continue through mid-morning mainly
  across northwestern IA before focusing south of U.S.
  Highway-20.

- Near normal temperatures continues the rest of the week with
  low rain chances on Wednesday, but significantly higher
  chances from Thursday night in Friday. Friday`s risk could
  bring a low severe weather risk by the evening.

&&

.UPDATE...
Issued at 348 AM CDT Tue Sep 15 2026

A much quieter start to the morning continues with the main concerns
being a few spotty sprinkles to very light showers and areas of
locally dense fog. Starting with the fog, lighter surface winds
along with lingering low level moisture from yesterday`s rain have
led to a few patchy areas of fog mainly across portions of far
eastern SD and southwestern MN. Current thinking is as northwesterly
winds strengthen with the 850mb cold front, most of the fog should
dissipate closer to daybreak. Moving on to the precipitation, a
little lingering lift ahead of the previously mentioned boundary is
working with a weak LLJ to spur some spotty activity this morning
mainly across northwestern IA. While widespread development is not
expected, can`t rule out some very light accumulations at times
through mid-morning (9am-10am) before this activity focuses south of
U.S. Highway-20. Otherwise, should see cloud coverage gradually
decrease from northwest to southeast with the cold frontal passage
by late morning as highs approach the upper 60s to low 70s for the
day. Lastly, with lighter surface winds expected later tonight;
can`t rule out some additional areas of fog.

&&

.DISCUSSION...
Issued at 122 PM CDT Mon Sep 14 2026

THIS AFTERNOON: Showers and isolated thunderstorms continue early
this afternoon with considerable cloud debris across the CWA. Latest
short term guidance continues to struggle to clear out enough of the
warm sector as the prevalence of a persistent 40 knot LLJ through
the CWA may just be too strong to overcome.  This may result in a
much lower surface based storm threat in the far southern CWA. There
may still be narrow window, but feel this may end up closer to I-80
than Highway 20. Further west, a surface cold front continues it`s
trek southeast.  Clearing ahead of this front in south central SD
might be just enough to spark a thunderstorm or two towards
Chamberlain and Gregory late this afternoon.  Any storm should
weaken quickly as it moves east.

TONIGHT:  While stronger surface based storms may just be south of
the CWA, we`ll need to watch for a lower probability elevated storm
risk late in the evening and early in the overnight hours.  A
secondary wave moves into Nebraska after 04Z, with soundings showing
at least the potential for a few stronger updrafts when lifted off
the 850:800 mb layer early in the overnight.  Given reasonable shear
at that time, an isolated large hail threat could develop over the
far southeastern portions of the CWA. The cold front will push
through the remainder of the CWA overnight, with a cooler northwest
wind developing.

TUESDAY: High pressure will be in control of the CWA on Tuesday,
with variable cloud cover leading to near normal highs around 70
degrees.

WEDNESDAY: Mid-lvl flow turns slightly to the southwest on
Wednesday, allowing modest return flow to push low-lvl moisture back
northward. While lift itself looks weak, a few showers and isolated
storms may develop through the day.  Soundings also show a high
probability for lower stratus which may limit the overall
temperature climb in the afternoon.

THURSDAY-FRIDAY: A similar setup continues for Thursday with broad
but weak warm advection persisting through the Tri-State area on
Thursday. Occasional light showers may develop north of a stalled
warm front over central and eastern Nebraska.  With low-lvl
temperatures climbing slightly, we may see a small uptick in high
temperatures towards the mid-upr 70s. The fly in the ointment
here is the persistent southeasterly surface wind and cloud
cover, which could lower the high temperatures towards the
lower to middle 70s instead.

By late Thursday night and Friday, a stronger wave ejects out of the
Central Rockies inducing stronger return flow and a sharpening of
moisture advection back into the Dakotas.  The nocturnal LLJ should
induce scattered to numerous non-severe showers and thunderstorms
into Friday morning.  With surface low pressure forming over the
western Dakotas during the day, a warm front may surge northward
across the CWA by mid-day allowing temperatures to quickly climb
into the 80s.  This increased instability combined with a cold front
that begins to move southeast late in the afternoon and evening
could spark a few strong to severe storms into Friday evening.
Though the quality of the warm sector, duration of morning
stratus, always make severe weather risks this time of year more
difficult to pinpoint this far out.

SATURDAY-SUNDAY: A stronger trough dips into the Dakotas for the
weekend which favors lowering temperatures and more isolated to
scattered shower development at times.  The severe weather risks
will remain low next weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 635 AM CDT Tue Sep 15 2026

VFR conditions will continue this TAF period. Besides some
lingering cloud cover across the Highway-20 corridor, most areas
should remain clear during the day. Otherwise, marginally breezy
northwesterly winds will gradually decrease this afternoon
becoming more light and variable overnight with the arrival of
a surface high.

&&

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

&&

$$

UPDATE...05
DISCUSSION...Dux
AVIATION...05