Spencer, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

634
FXUS63 KFSD 120319
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1019 PM CDT Wed Jun 11 2025

.KEY MESSAGES...

- Scattered thunderstorms expected to redevelop near I-90 and
  drift northward overnight. Locally heavy rain and small hail
  possible.

- More showers and thunderstorm are expected throughout the day
  on Thursday with the potential for strong to severe storms
  during the afternoon to evening hours. The primary risks will
  large hail up to (up to 1.5") and strong winds between 60-70
  mph.

- Locally heavy rainfall is possible with tonight`s and
  Thursday night`s developing activity. Accumulations between
  0.25" to 0.75" of an inch of rainfall is expected along and
  north of I-90 through Friday morning with isolated pockets of
  up to 1.5 inches possible across southwestern MN.

- Temperatures rise through the upcoming weekend, bringing
  additional thunderstorm risks by Sunday and into next week.
  Monitor for strong storm potential.

&&

.DISCUSSION...
Issued at 340 PM CDT Wed Jun 11 2025

CURRENTS & TONIGHT: Another warm day continues! Taking a look across
the area, a line of showers and thunderstorms has developed roughly
along a Tyndall to Sioux Falls to Marshall, MN line this afternoon
mostly in response to portions of a mid-level shortwave intersecting
a 850-925 mb surface boundary. As this developing line of showers
and thunderstorms continues to push eastwards into areas east of I-
29 over the next few hours, the presence of a weak LLJ will lead to
occasionally strong wind gusts up to 60 mph along with pockets of
locally heavy rain in the outlined areas. With this in mind, quick
accumulations up to 0.25" of an inch will possible mainly along the
MN/IA line ahead of this line. From here, we`ll likely see this line
exit our area closer to 3 pm as the aforementioned surface boundary
continues to push southwards towards the U.S. Highway-20 corridor
this evening. With a mostly undisturbed environment (1000-1500 J/kg
MLCAPE and 25-35 kts of bulk shear) south of U.S. Highway-18 and dew
points in the 60s, could see additional strong to severe storms
develop along portions of the Missouri River Valley and the Highway-
20 corridor this evening.

With mid-level lapse rates close to 6.5 degrees C/km and "inverted
V" characteristics in the soundings at KSUX, any developing semi-
discrete cells could produce large hail up to Ping-Pong balls (1.5")
and damaging wind gusts up to 70 mph as they merge into multi-
cellular clusters. As these storms continue to develop, expect this
activity to follow the 850 mb front northwards between 6 pm to 10 pm
and gradually weaken as they encounter a more stable environment
along and north of I-90. From here, we`ll likely see scattered
showers with isolated thunderstorms persist across areas north of I-
90 overnight with the focus shifting towards locally heavy rainfall.
With warm cloud depths of 10kft, slower storm motions, and mean wind
vectors parallel to the surface boundary; lingering showers and
thunderstorms could produce efficient rainfall rates between 0.10" to
0.25" of an inch at times according to the HREF with the highest
accumulations expected across southwestern MN. With this in mind,
could see some localized ponding on roadways and localized flash
flooding in urban/low lying areas.

THURSDAY-FRIDAY: Heading into Thursday, the severe risk and heavy
rainfall threats will be highly dependent on where the retrograding
surface boundary end up after tonight. However, similar to the
previous package; it does seem like 11.12z guidance has things
developing north of I-90 with a focus being along and north of the
U.S Highway-14 corridor as another mid-level wave intersects the
surface boundary. With this in mind, expect scattered showers with
isolated thunderstorms to persist for much of the morning hours as a
strengthening LLJ parallels the 850 mb front along and north of I-
90. The risk for strong to severe storms will increase from the
early afternoon to the evening (between 3pm to 11 pm) as the surface
boundary lifts retrogrades northwards and intersects an approaching
mid-level wave in the warm air advection (WAA) wing. With about 800-
1200 J/kg of instability and 35-45 kts of bulk shear to work with, a
few developing semi-discrete cells could become severe mainly north
of I-90 with large hail being the primary threat as mid-level lapse
rates approach 6.5 degrees C/kg.

Similar to today, locally heavy rainfall with developing storms will
also be a threat especially in the areas that received the most
rainfall overnight. Rainfall amounts could vary between 0.25 to 0.75
of an inch with pockets of up to 1.5 inches into Friday. From here,
expected showers and thunderstorms to gradually come to an end
during the morning hours of Friday as most of the activity pushes
east of the area.

SATURDAY ONWARDS: Heading into the extended period, an upper-level
ridge will slide eastwards into northern plains and flattens into
the early part of next week, with at least one more weak wave
"riding the ridge" by Sunday. A more defined mid/upper level trough
develops by Tuesday and slides into the northern plains. Models
continue to diverge in terms of the details with this trough and
associated surface low, but this could bring additional shower and
storm chances to the region. Although details are uncertain, this
pattern is conducive to periods of showers and thunderstorms through
the midweek. Machine learning and other guidance indicates that some
strong to severe storm potential exists. Lastly, temperatures will
continue to sit in the mid 70s to mid 80s for highs through
Tuesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1015 PM CDT Wed Jun 11 2025

Scattered showers and thunderstorms remain focused either side
of I-90 late this evening. As the low-lvl jet refocuses and
shifts northward, additional showers and thunderstorms are
likely to develop and gradually move north and northeast into
Thursday morning. Brief reductions in visibility to MVFR levels
is possible.

Stratus may attempt to build into areas north of I-90 and
especially near Highway 14 through mid-day Thursday, elsewhere
VFR conditions are expected. A warm front lifts as far north as
I-90 by mid-afternoon shifting east southeast winds towards the
south.

Isolated to scattered storms may try to redevelop by mid-late
afternoon in central SD and along the Buffalo Ridge.

&&

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

&&

$$

DISCUSSION...05
AVIATION...Dux