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Forecast Discussion for FSD NWS Office

856
FXUS63 KFSD 210740
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
240 AM CDT Sun Jul 21 2024

.KEY MESSAGES...

- Fog continues to develop early Sunday morning and may result
  in visibilities falling below 1 mile at times into mid-
  morning Sunday.

- Isolated to scattered daily showers and thunderstorms
  continue through Tuesday. Severe storms are not expected, but
  some small hail and occasional funnels or landspout tornadoes
  could be possible.

- Temperatures begin to warm for the second half of the week
  through next weekend. High probabilities (>70%) for
  temperatures at or above 90 degrees are likely along and south
  of the James River valley.

&&

.DISCUSSION...
Issued at 237 AM CDT Sun Jul 21 2024

THIS Morning: Very light winds and temperatures cooling into the
lower 60s is allowing fog to once again develop throughout the Tri-
State area.  Current web cameras and satellite views continue to
show this fog remaining very shallow in nature.  Fog will continue
to spread this morning, and could result in advisories needed into
mid-morning.   Further north, we`re seeing some remnant high clouds
associated with a couple subtle lobes of vorticity drifting
southeast within the northerly upper level flow.  Can`t rule out an
isolated shower popping up prior to daybreak, but feel chances are
low.

TODAY: Another day that will start out with some fog, and then
transition to warm and partly sunny skies by mid-day.  However we`ll
watch a series of very weak impulses drop southward out of eastern
North Dakota and western Minnesota through the day.  Perhaps the
strongest piece of vorticity is currently approaching the ND/SD, and
will eventually reach the Highway 14 corridor by mid-day.   Other
waves will arrive later in the afternoon, and with temperature
reaching convective temperatures by early to mid-afternoon, isolated
to scattered convection will develop and meander southward into the
early evening.  Instability is again not expected to be significant,
with tall and thin CAPE profiles with upwards of 800-1000 J/KG. Low
level flow below 800 mb is minimal at best and overall effective
shear is also minimal.  Thus the severe weather risk should remain
minimal, with the only potential issue being the risk for very
isolated brief funnels or landspout development along
boundaries.

TONIGHT: Most activity will wane once again once sunset arrives,
with some lingering showers tied more closely to any piece of
vorticity still drifting towards Nebraska late in the evening.
Surface winds remain very light into Monday morning and dew points
remain in the lower 60s, so fog will again be possible.

MONDAY:  Rinse and repeat forecast for Monday as yet another wave of
weak vorticity pieces arrives from the north to northwest by mid-
day.  Isolated to scattered non-severe convection again develops and
drifts southeast before losing diurnal support late in the evening.

TUESDAY: Very minor shortwave ridging moves in early Tuesday and may
result in the best chances for afternoon convection also shifting
slightly further east. Currently the highest PoPs (30%) are focused
east of I-29. Temperatures warm into the lower 80s in many areas,
potentially approaching the mid-80s west of the James River.

WEDNESDAY-SATURDAY:  One final shortwave moves through the Western
Great Lakes early on Wednesday and will finally push the daily risks
of afternoon convection away from the area. Some afternoon CU is still
expected Wednesday afternoon, which could develop into some sprinkles
due to incoming weak cold air advection.

Mid-lvl heights increase through the remainder of the work week and
into the upcoming weekend.  High pressure centered over the Great
Lakes will keep surface winds more from the southeast into Friday,
preventing any substancial rise in temperatures.  However we`ll see
a return of southerly flow on Friday and then southwesterly flow by
the weekend. Strong warm advection spreads through the Plains by the
weekend, and while not a climatologically significant airmass for
this time of the year, will result in high temperatures returning to
the upper 80s to lower 90s. The rise in seasonal evapotranspiration
will push dew points towards the 70 degree mark for next weekend
and results in heat index values climbing further through the 90s.
Overall no change in ensemble guidance, with all three major ensembles
suggesting a greater than 70% chance of 90 degree temperatures along
and west of the James River valley into the mid-Missouri River
valley.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1030 PM CDT Sat Jul 20 2024

Expect fog and stratus to develop through the overnight hours
into early Sunday morning with calm or very light winds. Most
hi-res guidance shows widespread visibility less than one mile
(especially for areas along/east of the James River). However,
kept mention in TEMPO groups at KFSD and KSUX to one mile with
some uncertainty in the extent of visibility less than one mile.
Will continue to monitor trends. MVFR/IFR conditions prevail
through at least early Sunday morning.

Similar to Saturday, expect stratus to linger into the mid/late
morning hours. Isolated to scattered showers and storms develop
by early afternoon and increase in coverage through the day.

Wildfire smoke aloft will lead to hazy skies as areas of thick
smoke advect into the region from the north.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...SG

NWS FSD Area Forecast Discussion