036
FXUS63 KFSD 120527
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1227 AM CDT Tue May 12 2026

.KEY MESSAGES...

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

- Critical fire danger expected Tuesday 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. Thursday and Friday warm into the mid
  80s to lower 90s.

- Dry weather continues this week. Uncertainty remains, but
  chances for showers and storms are steadily increasing for
  late week into the weekend.

&&

.UPDATE...
Issued at 908 PM CDT Mon May 11 2026

Keeping an eye on temperature trends this evening, with temperatures
still in the 70s and lower 80s. Do expect temperatures to fall into
the 50s tonight with WAA and southerly winds overriding dew points
in the 30s and 40s. Main change to the forecast this evening was to
refine coverage of pops and sprinkles/showers tonight into Tuesday
morning based on some of the latest CAMs. Biggest question remains
how much will even reach the ground with soundings showing a stout
sub cloud layer, so coverage may still be too robust. Reflectivity
has increased over the last hour by Winner, SD but have not seen
any indication that anything has reached the ground. With the
refinements to pops, did update cloud cover as well with some guidance
struggling in coverage of high clouds. Still partly to mostly cloudy
skies tonight.

Gusts have tapered off this evening, but expect winds to remain
breezy with gusts returning with the cold front and CAA tonight. No
changes at this time to tomorrow`s forecast or headlines - Red Flag
Warning in effect from noon to 9 PM CDT Tuesday. Not expecting the
need for any wind headlines, but may need to reconsider if winds
trend higher.

&&

.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 /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1217 AM CDT Tue May 12 2026

Isolated sprinkles and showers have developed, with very
isolated lightning strikes. Confidence is low in impacts to
terminals for both showers and TS, so omitting mention. KFSD may
see some VCTS before 07z, but again, too low confidence to
include. VFR conditions are expected, and RA may be hard to come
by with the very dry sub cloud layer.

Winds are the main concern through the period as a cold front
moves south across the area overnight. Sfc winds shift from
southerly to northwesterly, with gusts increasing to 30-35+
knots during the day Tuesday. LLJ this morning leads to LLWS as
the winds shift both at the sfc and aloft with the jet.

VFR conditions continue through the day Tuesday and into Tuesday
night with high clouds around the region. Winds taper down after
sunset, becoming light and somewhat variable toward the end of
the forecast period.

&&

.FIRE WEATHER...
Issued at 336 PM CDT Mon May 11 2026

A Red Flag Warning is in effect from Tuesday at Noon until 9 pm CDT
for southeastern South Dakota, northeastern Nebraska, southwestern
Minnesota, and northwestern Iowa. A very dry air mass settles over
the region behind an early morning cold front. Relative humidity
values are expected to fall to less than 25% with most of the region
seeing values as low as 19-22%. In addition, northwesterly winds
will increase behind the front. Sustained winds of 20-30 mph will be
widespread along with gusts of 35-40 mph. The combination of strong
winds, very low relative humidity, and warm highs in the 70s is what
prompted the Red Flag warning.

Wednesday conditions remain very dry and warm with highs in the mid
70s to low 80s. However, winds will be light and variable, thus
negating the need for a fire headline. However, please continue to
use caution to avoid fire starts.

Thursday conditions will again be favorable for fire with southerly
sustained winds at 25-30 mph and gusts 35-40 mph. A few isolated
gusts of 45+ mph are also possible. Additional fire headlines
may be necessary. Please check back through the week for
updates.

&&

.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...SG
DISCUSSION...AJP
AVIATION...SG
FIRE WEATHER...AJP