145
FXUS63 KFSD 121115
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
615 AM CDT Tue May 12 2026

.KEY MESSAGES...

- Isolated showers/sprinkles continue through the early morning
  hours. A few rumbles of thunder are possible; severe weather
  is not expected.

- Critical fire danger expected today with northwest winds
  gusting 35-40 mph and relative humidity values at or below
  25%. Red Flag Warning is in effect from Noon until 9 pm CDT.

- Elevated to near critical fire weather concerns again
  Thursday as wind gusts increase to 35-45 mph.

- Warmer conditions are expected this week with highs 10 to 20
  degrees above normal. Friday and Saturday warm into the mid
  80s to lower 90s.

&&

.UPDATE...
Issued at 310 AM CDT Tue May 12 2026

A fast moving wave to the northeast will swing weak lift and
instability through the area early this morning. This will result in
spotty showers and very isolated rumbles of thunder. By about 15z
this activity should be out of the area, although some weak lift
does linger from about Sioux City towards Ida Grove through about
18z.

Behind this wave strong mixing is expected with temperatures
climbing into the 70s. With afternoon relative humidity expected to
drop as low as about 18-25 percent along with wind gusts of 30 to 40
mph, critical fire weather conditions are expected. The most
susceptible locations will be warm season grasses that are just
beginning to green up. However, even the shorter cool season grasses
that have greened up are already beginning to show signs of stress
with little precipitation since the widespread rain event 2 weeks
ago. Extreme care should be taken with outdoor activities that
involve fires or could spark a fire.

Otherwise the next day of concern for fire weather will be Thursday
when southerly winds may gust to 35 to 45 mph. What could offset
this will be some mid level moisture and lift ahead of an incoming
wave that will likely bring an increase in cloud cover as well as
scattered showers and isolated thunderstorms. While very rare in
this area, there is at least a small chance for some dry lightning
given the dry low levels on Thursday. Something to keep an eye on.

&&

.DISCUSSION...
Issued at 336 PM CDT Mon May 11 2026


Despite the recent green up, lack of beneficial rain in the
past ten days or so has resulted in some of the growth beginning
to dry out. Combine this with highs in the 70s to 80s
(increasing from east to west), relative humidity falling to 30%
or less, and southerly winds gusting 20-30 mph will result in
elevated fire concerns for this afternoon. Please use caution
with sources of sparks and report any fires immediately. Lows
for tonight will be warm, in the 50s to 60s.

This evening and overnight the strongest winds will shift east of I-
29 ahead of an approaching cold front. As it does so there will be a
very brief lull in winds as they turn to the northwest. Along
with the frontal passage is a low chance (<20%) of light rain.
However, a very dry airmass will be present over the region.
Limiting what makes it to the ground to just very light
sprinkles if anything. Winds will increase through the morning,
reaching their peak in the early afternoon at 35-40 mph. With
soundings indicating steep low level lapse rates, deep mixing
tapping into a 35-40 kt LLJ, and northwest winds aloft well
aligned, there is potential for winds to overperform. After
discussion with neighbors, have blended in a little RAP13 and
HRRR into the NBM to boost peak winds and gusts. This results in
sustained winds very near to Wind Advisory criteria, while
gusts remain shy of criteria by 2 or 3 kts. Collaboration with
neighbors came to the conclusion to hold off on wind headlines
at this time, but will monitor the trends with the upcoming
model runs.

Highs will be slightly cooler thanks to CAA behind the front, in the
low to upper 70s. However, the previously mentioned dry air over the
region will work to decrease the relative humidity values to less
than 25% for most of the region. The combination of strong winds and
low humidity will result in High Grassland Fire Danger for Tuesday.
As such, have issued a Red Flag Warning for southeastern South
Dakota, northeastern Nebraska, southwestern Minnesota, and
northwestern Iowa on Tuesday from Noon until 9 pm CDT. More on
this in the Fire Weather Discussion below.

Wednesday the dry air mass remains in place as an upper ridge and
surface high pressure move over the region. Highs will climb into
the mid to upper 70s with some 80s possible along the southern
Missouri River Valley. Relative humidity values will once again fall
to less than 25% for most of the region, however winds will be light
and variable. At this time there is no plan for a fire headline.
Despite that, please continue to use caution so as not to spark a
fire. Thursday relative humidity values recover slightly, but remain
less than 30% for the entire region, with central South Dakota
seeing values of 25% or less. Winds will be strong out of the
south, with sustained winds 25-30 mph and gusts 35-40 mph. A
few isolated gusts of 45+ mph are also possible. These
conditions will lead to the Grassland Fire Danger to increase to
High to Very High. Please keep an eye on the forecast for
Thursday, as fire and wind headlines may be necessary.

In addition Thursday night into Friday morning an upper trough will
pass north of the region. As it does so it will drag a cold front
through that may work to trigger some showers and thunderstorms.
Uncertainty in strength and areal coverage remains high as models
begin to diverge. Additional chances for showers and thunderstorms
continue into the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 614 AM CDT Tue May 12 2026

Scattered sprinkles and very light showers will continue through
mid to late morning, drifting southeastward. Otherwise, VFR
conditions are expected. The main concern will be northwest
winds gusting to 30 to 40 mph late this morning into the
evening.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning from noon today to 9 PM CDT this evening for
     SDZ038>040-050-052>071.
MN...Red Flag Warning from noon today to 9 PM CDT this evening for
     MNZ071-072-080-081-089-090-097-098.
IA...Red Flag Warning from noon today to 9 PM CDT this evening for
     IAZ001>003-012>014-020>022-031-032.
NE...Red Flag Warning from noon today to 9 PM CDT this evening for
     NEZ013-014.

&&

$$

UPDATE...08
DISCUSSION...AJP
AVIATION...08