Spencer, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

864
FXUS63 KFSD 141140
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
640 AM CDT Sat Jun 14 2025

.KEY MESSAGES...

- A Dense Fog Advisory has been issued for portions of northwest
  Iowa, southwest Minnesota, and south central and southeast
  South Dakota until 9 am this morning. Please drive to
  conditions if you encounter fog while on the road.

- An active pattern looks to bring continued chances for showers
  and storms for the weekend and most of next week. While some
  details remain uncertain, continue to monitor the forecast for
  strong to severe storms and heavy rain potential.

- Temperatures look to remain in the 70s, 80s, and low 90s today
  through next week.

&&

.UPDATE...
Issued at 437 AM CDT Sat Jun 14 2025

After looking at latest cameras and observations across the
area, have decided to issue a Dense Fog Advisory for portions
of northwest Iowa, southwest Minnesota, and south central and
southeast South Dakota. Reduced visibilities down to a quarter
of a mile is expected in the dense fog. The Advisory is in
effect until 9 am this morning. Please drive to conditions if
you encounter fog while on the road.

&&

.DISCUSSION...
Issued at 346 AM CDT Sat Jun 14 2025

Today: Low level stratus continues to sit over the bulk of the area
this morning. This has kept temperatures from falling too quickly as
current temperatures remain in the 50s to low 60s. Shouldn`t see
temperatures budge that much more before sunrise. Patchy fog has
developed along the spine of the Buffalo Ridge and looks to remain
across this area into the morning hours. Will continue to monitor
the potential for needing to issue a Dense Fog Advisory for this
area.

Should see the fog lift through about mid morning and the low level
stratus will retreat northwards through the rest of the morning
hours. This will allow for high temperatures to reach the mid 70s to
low 90s from northeast to southwest. A surface boundary will be
slowly drifting northwards throughout the day and may result in
thunderstorm development this afternoon. Storm development is highly
conditional though as very weak forcing for ascent will be in place.
Tough to say where storms will develop but with the previously
mentioned boundary in place, think that the most likely area to see
storms is along and south of I-90, mainly across parts of southeast
South Dakota, southwest Minnesota, northwest Iowa, and far northeast
Nebraska where little to no capping is expected. Deep layer shear
will be quite weak with a magnitude of less than 30 knots.
Instability on the other hand will be sufficient with CAPE values up
to around 2,000 J/kg. Should storms form during the afternoon, think
they could be lower end severe storms with damaging winds up to 60
mph being the primary hazard. Large hail to the size of half dollars
will be the secondary hazard but will depend on storms remaining
marginally discrete. Pockets of heavier rainfall is possible in the
storms as well with localized amounts up to around an an inch of
rain possible in storms that may track/train over any individual
location.

While the afternoon storms look to exit the area during the evening
hours, there could be a second round of storms pushing into the area
from the west but confidence is low in this potential as only the
00z HRRR and NAM Nest show this possibility. These models shows a
line of storms pushing into the Missouri River Valley but soundings
show that these storms will be encountering greater capping which
should limit the severe storm potential. Uncertainty further
increases heading into Saturday night as the potential for isolated
severe storms along with heavy rain/flash flooding may be on the
table. A weak mid level short wave trough will be slowly pushing
into the area from the west. This will result in weak low level warm
air advection which may result in elevated storms developing along
the 925 mb boundary. The uncertainty for this potential lies in how
capped the atmosphere will be from lifting from roughly 925mb. Shear
values remain on the weaker side though there could be just enough
tilting of updrafts thanks to stronger winds above 300 mb to promote
a large hail risk with large hail up to the size of quarters being
possible. At the same time, CAPE values will remain large with
values up to 1,500 to 2,000 J/kg. However, the main risk will be the
potential for heavy rainfall as the mean flow will be weak, on the
order of about 15 knots. With the mean flow paralleling the 925 mb
boundary, this could result in training thunderstorms along the
boundary that could produce rainfall values up to 1-2 inches or
potentially more possible per the HREF probability matched mean. The
most likely area to see this potential heavier rainfall will be
locations north of I-90, especially towards east central South
Dakota and southwest Minnesota. Do want to stress that this is
highly conditional and there remains great uncertainty in this
potential. Please continue to monitor the latest forecast for the
most up to date information.

Sunday through Wednesday: Weak shortwave troughs will continue to
round the top of an upper level ridge sitting over the southern
CONUS. This will lead to chances for showers and storms each day as
sufficient moisture, and associated instability, will be in place.
Shear looks to remain weak on Sunday though any shortwave trough
passing through could spark another round of showers and storms.
Some of these storms could be strong to severe and be capable of
damaging winds and large hail during the afternoon hours. Warm
temperatures above the ground may keep convective coverage more
isolated given some capping remaining in place though. A rinse and
repeat of storm potential is expected for Monday though looks like
storm chances will increase after dark as medium range guidance is
in somewhat decent agreement in a slightly stronger shortwave trough
pushing into the Northern Plains. This round of showers and storms
will again posses the potential for strong to severe storms but also
a heavy rain threat as precipitable water (PWAT) values climb up to
the 90th percentile of climatology per the NAEFS ensemble. The
ensembles also support this potential as they show a 50-80% chance
for rainfall amounts to exceed a tenth of an inch on Monday.

No break in the potential for rain as another shortwave trough will
eject east of the Rocky Mountains and into the Northern Plains
Tuesday night. The ensembles support this potential as they show a
40-80% chance for rainfall amounts to exceed a quarter of an inch of
rain on Tuesday. This will also continue a heavy rain threat as well
though specific details are uncertain at this time. Given how this
shortwave trough looks to be a slower moving trough, this will
continue rain chances, and an associated heavy rainfall threat,
through Wednesday as well. Despite the daily chances for rain, high
temperatures look to remain near to above average in the upper 70s,
80s, and low 90s. Tuesday and Wednesday will be the coolest days.

Thursday through Friday: The upper level ridge over the southern
CONUS will rebuild for the end of the week. This will keep an active
northern jet aloft through the Northern Plains. This could be
supportive of additional rounds of showers and storms, some of which
could be strong to severe, as shear values increase. This potential
is supported by the machine learning guidance as this guidance does
show modest probabilities for severe storm chances. Aside from rain
and storm potential, temperatures look to remain in the 80s and 90s
across the area.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 640 AM CDT Sat Jun 14 2025

Low level stratus and fog begin the TAF period this morning. The
stratus covers the vast majority of the area this morning and is
sitting at MVFR/IFR/LIFR levels. Visibilities range the entire
flight category spectrum from VFR all the way down to LIFR levels.
Latest thinking is that the stratus and fog will lift through the
mid morning hours as the sun continues to rise. A boundary currently
sitting close to I-80 will push northwards and turn winds to out of
the south in its wake. The boundary looks like it will push up to
around I-90, keeping easterly flow going north of the interstate.
Once the stratus clears the area, chances for showers and storms
will be possible this afternoon and evening mainly along and south
of I-90. Have included PROB30 groups in both KFSD and KSUX`s TAFs.
Additional chances for showers and storms is possible during the
overnight hours though it is uncertain where storms may develop.
Will keep an eye on trends throughout the day and night.

Will also keep an eye on trends with the stratus throughout the day
today and may make amendments accordingly if the stratus lingers
longer than currently expected.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 9 AM CDT this morning for SDZ050-
     060>071.
MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ071-072-
     080-081-089-090-097-098.
IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ001>003-
     012>014.
NE...None.

&&

$$

UPDATE...Meyers
DISCUSSION...Meyers
AVIATION...Meyers