589
FXUS63 KFSD 161122
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
622 AM CDT Fri May 16 2025

.KEY MESSAGES...

- Strong winds and persistent rain to rain showers are expected
  to drift back southward on Friday.

- Wind gusts over 50 mph may be possible at times through Friday
  afternoon. Wind advisories have been issued and local upgrades
  to high wind warnings possible.

- Counties along the Missouri River may see wind gusts up to 60
  mph. These counties have been upgraded to a High Wind
  warning.

- After a quiet and cool weekend, moderate to high
  probabilities of rain (90%) return Monday and Tuesday.

&&

.DISCUSSION...
Issued at 340 AM CDT Fri May 16 2025

TODAY: Looking at GOES upper water vapor imagery, we can see the
upper low pressure spinning over the intersections of South Dakota,
North Dakota, and Minnesota. This is expected to slowly move
northeast today. Looking at the surface we see the associated
surface low pressure sitting over eastern North Dakota. There is
high agreement in short range guidance that this low will sink south
and east this morning. As it does so, moisture will wrap around the
low, and light rain showers will overspread the region after sunrise
today. There is just enough elevated instability that you may hear a
rumble or two of thunder with these, but severe weather is not
expected. Showers will gradually taper off this evening. Additional
accumulation of around a tenth or two for most places.

In addition to showers today we are expecting continued strong winds
out of the west to northwest. This is in response to the deepening
low increasing the SPG. Sustained winds will blow between 30-40 mph
with frequent gusts 45-55 mph. The highest gusts are expected from
Gregory county in south central South Dakota, along the
Missouri River counties and south into Nebraska. In this area
gusts to 60 mph are possible. ESATs tables indicate the wind
speed in the 850-700 mb layer are at or very near maximum for
climatology. Soundings indicate we will easily be mixing this high
today. In addition, soundings indicate the winds at the top of the
mixed layer will be 50-55 kts. If we meet mixing potential, that
translates to wind gusts at the surface that meet High Wind Warning
criteria. The conclusion is that these counties will be borderline
for High wind warning, and after coordination with neighbors, I have
decided to upgrade those few counties to a High Wind Warning this
afternoon. As far as the rest of the county warning area, the Wind
Advisory looks to be in good shape. However, we will continue to
monitor the trends to see if an expansion to the High Wind Warning
is necessary. Winds will slowly decrease overnight tonight and
through the day Saturday.

Highs today will be cool, in the low to mid 50s. Areas of
northwestern Iowa will be the warmest and may see temperatures
reaching the low 60s. Overnight lows will be in the upper 30s to mid
40s.

SATURDAY-SUNDAY: Weak upper ridging and surface high pressure pull
in some dryer air in the mid-levels early Saturday morning, ending
showers. However, the lower levels remain saturated, resulting
in a fairly thick stratus layer that will hang around for most
of the day Saturday. By mid-afternoon, as the larger low
pressure system continues to pull away, we`ll begin to see more
dry air move in, slowly eroding the clouds. By the late
afternoon, some peaks of sunshine are expected.

As mentioned, winds will still be breezy Saturday morning with
northwest gusts 20-25 mph. Those winds are expected to slowly
decrease through the day Saturday, becoming light and variable after
sunset. High temperatures will be on the cool side, with areas north
of I-90 expected to see mid 50s to low 60s. South of I-90,
especially along the Missouri River, highs will reach the mid
to upper 60s. Lows will be chilly, in the 30s. For most areas,
this is around 10 to 15 degrees cooler than average for this
time of year.

Zonal upper flow for Sunday with a shallow embedded wave may
bring some light showers to central South Dakota Sunday morning.
These are expected to be very light, with a hundredth or two of
accumulation. Easterly winds with weak WAA will warm the 850 mb
layer to 6-10 deg C. Mixing that down we can expect highs in
the mid to upper 60s with 70s possible along the Missouri River
and northwestern Iowa.

Meanwhile, to the west we see an upper trough digging over the
Rockies. This trough begins to eject out onto the plains by late
Sunday afternoon. Easterly winds increase Sunday afternoon in
response to the tightening SPG ahead of this next system. Winds
remain breezy overnight with gusts of 20-25 mph. Also overnight, the
surface low moves out of Colorado into western Nebraska and
accelerates northeast toward eastern South Dakota. We will find
ourselves in the warm sector of this system, with strong WAA
triggering showers beginning late Sunday night into Monday.

MONDAY-THURSDAY: There is good agreement in mid-range guidance on
the overall track of the low, with the EC continuing to bring the
track just a bit farther north than the others. Ensembles indicate
high probability of receiving an inch or more of rain, between
80- 100%, from onset early Monday through ending late Tuesday.
Currently, the better dynamics look to remain south of our
region, keeping the severe weather risk low. However, shifts in
track of this system could bring stronger storms to the region.
We will continue to monitor the trends.

Conditions dry out as an upper ridge builds in for Wednesday. Here
model guidance begins to diverge. All indicate a fast moving system
for Friday, but agreement on timing and track are low. Temperatures
during this time will remain on the cool side of average, in 50s and
60s. Finally warming in the the 70s again by Thursday and
Friday.&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1041 PM CDT Thu May 15 2025

Most of the area will see VFR conditions overnight, although
MVFR stratus will move into the US Hwy 14 corridor overnight.
This stratus sinks south through the day Friday, leading to
widespread MVFR to patchy IFR conditions. Showers on-going
tonight near US Hwy 14 will also move south and expand over the
area during the day Friday, so could see some MVFR visibility
with heavier showers.

Strong westerly winds continue, with gusts 30 to 40+ knots for
most of the period, tapering off after sunset Friday. Areas
along and south of I-90 could see some LLWS with gusts
diminishing overnight - although expect these to increase as we
approach/pass daybreak Friday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 622 AM CDT Fri May 16 2025

VFR conditions will degrade to MVFR and patchy IFR as thick stratus
and rain showers move in this morning from the north. Rain is
expected to become more scattered in the afternoon before tapering
off this evening.

Winds are strong out of the west, gradually becoming northwest this
afternoon. Sustained winds of 25-35 kts with frequent gusts 40-50
kts are expected. Localized gusts of 55 kts are possible. The
winds will be strong across the entire region, but south central
South Dakota and along the Missouri River and south will have
the highest gusts. Winds very gradually dissipate overnight and
through the day on Saturday.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 7 PM CDT this evening for SDZ038>040-
     052>062-064>067.
     Wind Advisory until 7 PM CDT this evening for SDZ071.
     High Wind Warning until 7 PM CDT this evening for SDZ050-063-
     068>070.
MN...Wind Advisory until 7 PM CDT this evening for MNZ071-072-080-
     081-089-090-097-098.
IA...Wind Advisory until 7 PM CDT this evening for IAZ001-002.
     Wind Advisory until 7 PM CDT this evening for IAZ003-012>014-
     020>022-031-032.
NE...High Wind Warning until 7 PM CDT this evening for NEZ013-014.

&&

$$

DISCUSSION...AJP
AVIATION...AJP