870
FXUS63 KFSD 120837
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
337 AM CDT Mon May 12 2025

.KEY MESSAGES...

- Very warm, very dry, and breezy conditions are expected
  through Wednesday. Highs in the upper 80s to lower 90s may
  approach record levels in some areas.

- A Red Flag Warning is in effect from noon until 9 pm this
  evening for southeast South Dakota, southwest Minnesota, and
  parts of northwest Iowa due to strong south wind, low relative
  humidity, and dry fuels. Fire danger may vary greatly over
  short distances as it will depend on greenness of local
  grasses.

- Shower and thunderstorm chances increase late Wednesday
  afternoon and evening with the passage of a cold front.
  Isolated severe storms will be possible along with brief heavy
  rainfall.

- The latter half of the week will bring relief from the heat
  with decreasing rain chances into next weekend.

&&

.DISCUSSION...
Issued at 334 AM CDT Mon May 12 2025

Another hot, dry, and breezy day in store across the area as upper
level ridging continues to dominate over the region. 850 mb
temperatures will be similar to yesterday - 16 to 21 C - running
near the max percentile with respect to climatology. This will play
out to highs once again in the upper 80s to lower 90s - which will
be near records for this date. While it will once again be breezy
today, model soundings would suggest slightly lower winds than
yesterday with winds at the top of the mixed layer running closer to
25 kts (lower in  northwest Iowa). Even so, with the exception of
northwestern Iowa, look for afternoon winds gusts of 30 to 40 mph
across the area. This along with the very dry airmass will result in
critical fire weather conditions across much of the area, and the
current Red Flag Warning for southeast South Dakota, southwest
Minnesota, and parts of northwest Iowa remains valid.

Not a whole lot of change for Tuesday with highs again in the upper
80s to lower 90s, though winds look slightly weaker still as the SPG
weakens a bit and winds aloft decrease further. In addition, low
level moisture begins to increase slightly - boosting afternoon RH
just a bit. Even so, elevated to near-critical fire weather
conditions will remain across much of the area, though based on
the above will forego any fire weather headlines at this time.

One more warm day for Wednesday - this out ahead of an upper level
trough drifting eastward out of Rockies and an approaching surface
trough/cold front over western/central South Dakota. Low level
moisture will increase further still as dew points climb into the
lower to mid 50s. This will mitigate the fire danger somewhat. The
cold front tracks across the area on Wednesday evening/night.
Thunderstorms are expected to develop with this feature, with most
models indicating MUCAPE around 1500 J/KG. The better bulk shear
(behind the front) is offset from the higher instability, but with
mid level lapse rates around 7 C/KM cannot rule an isolated strong
to severe storm (SPC Day 3 Marginal). In addition, localized brief
heavy rain will be possible with model PWATs running in excess of
1.5" (WPC Day 3 Marginal ERO). Related to this, latest ensembles
indicate probabilities of 70-90% for greater than 0.5" of rainfall -
mainly west of Interstate 29.

Lingering showers and isolated thunderstorms will remain possible on
Thursday as the main upper level trough swings through the Northern
Plains. Temperatures will gradually be cooling with highs in the
upper 60s to mid 70s.

More typical Northern Plains spring returns for Friday through the
upcoming weekend with the upper level trough shifting into the Great
Lakes region, then into New England toward the end of the period.
Much cooler 850 mb temperatures feed into our area behind the
feature in a northwesterly upper level flow, with temperatures
dropping back to near to below normal through the period (highs 60s
to lower 70s). Models trend drier into the early part of the
weekend, then increasing chances for rain by the end of the weekend
as an upper level trough over the western CONUS shifts eastward -
though many details to work out this far out.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1011 PM CDT Sun May 11 2025

VFR through the period. The main concerns continue to center
around gusty southerly winds. Gusts of 20 to 30 mph remain
likely through the night. Monday will once again see gusts of 30
to 40 mph develop during the morning and continue through about
sunset.

&&

.FIRE WEATHER...
Issued at 334 AM CDT Mon May 12 2025

Hot, dry, and breezy conditions will continue across the area for
today - resulting in critical to near-critical fire danger.
Afternoon highs will be in the upper 80s to lower 90s, with
dewpoints just either side of 40, yielding RH values of 15 to 20
percent. Although winds may be slightly lower than yesterday, these
conditions will result in a very high fire danger for much of the
area and the current Red Flag Warning for southeast South Dakota,
southwest Minnesota, and parts of northwest Iowa remains valid.

Tuesday will see similar temperatures, though winds are expected to
be slightly less still. With a slight increase in low level
moisture, dew points will be higher, and afternoon RH will run
closer to 20 to 30 percent - bringing an elevated to near-critical
fire danger to most of the area. Low level moisture will continue to
increase on Wednesday, thus mitigating the fire danger somewhat. By
Wednesday evening, showers and thunderstorms are expected to develop
across the area, followed by cooling for the remainder of the week.

Of note with regard to the above, the fire danger through the period
will vary greatly over a small distances - dependent on the
greenness of local vegetation. In any event, precautions should be
taken to avoid the start and spread of wildfires for today and
Tuesday.

&&

.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
     IAZ001-002-012.
NE...None.

&&

$$

DISCUSSION...JM
AVIATION...08
FIRE WEATHER...JM