Spencer, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

764
FXUS63 KFSD 062050
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
350 PM CDT Fri Jun 6 2025

.KEY MESSAGES...

- Isolated funnels are possible through sunset across the area.

- Strong to severe storms are possible Saturday evening along
  and north of highway-14. Damaging winds up to 65 mph is the
  primary threat.

- Temperatures will warm to the 70s and 80s by the middle of
  next week. A few chances for rain are possible as well.

&&

.DISCUSSION...
Issued at 349 PM CDT Fri Jun 6 2025

A few light showers persist across the area this afternoon. With
weak instability values in place along with light winds in the
lowest 8,000 feet of the atmosphere, isolated weak funnels will be
possible. A Special Weather Statement (SPS) is in effect for the
entire area until 8:00 pm this evening due to the funnel threat.
Light showers will diminish after sunset as diurnal heating wanes.
Lows tonight will fall to low to mid 50s. The reprieve from rain
will be short lived as a mid-upper shortwave and surface low
pressure skirt by just south of our region in Nebraska Saturday
morning. This wave will bring low chances (<35%) of showers and
thunderstorms to areas along and south of the southern Missouri
River Valley, and east of I-29 Saturday morning through mid-day.
Dynamic parameters look to remain marginal (Bulk shear < 30 kts,
MLCAPE < 400 J/kg, Lapse rates < 6.5 C/km) and so severe weather is
not expected. A few rumbles of thunder are still possible, and
should any stronger updrafts develop locally heavy rainfall is
possible. Rainfall totals from this round should be a tenth or two
up to a quarter of an inch.

Saturday afternoon we`ll get a break in showers and some peaks of
sunshine. Light southwesterly winds will usher in WAA and a dry
boundary layer air mass. Temperatures in the 850 mb layer will warm
to 14-18 deg C. Good mixing will help surface temperatures rise to
the upper 70s to low 80s. While the rain may let up Saturday
afternoon, we do have a risk for some isolated funnels. Bulk shear
from 0-1 km is very weak, 15 kts or less, collocated with an area of
enhanced stretching potential for areas east of I-29. Here brief,
weak funnels could form Saturday afternoon. These funnels are
usually harmless and dissipate quickly. Risk for funnels will
decrease as we lose afternoon heating.

Meanwhile, over central Canada, a strong closed low will begin to
move southeast towards the Great Lakes region. From this low a cold
front will drape down through eastern North Dakota, through central
South Dakota, and into central Colorado. As this system continues to
move southeast, the cold front will move through our region
beginning Saturday evening. The afternoon rapid increase in
temperatures will result in increased elevated instability. Modest
MLCAPE of 800-1200 J/kg will be collocated with modest 0-6 km bulk
shear of 30-40 kts. The marginal dynamics will be aided by the
strong forcing provided by the cold front, resulting in isolated to
scattered strong to severe thunderstorms. Recall the dry air mass in
the boundary layer; this will result in "inverted V" shaped
soundings. The steep lapse rates from the surface to the LCL that
result will lead to high DCAPE of 1000-1500 J/kg. Considering the
dynamics, the greatest threat with any storms that develop will be
strong down draft gusts of 65 mph. Some small hail is also possible.
With mid-level flow parallel to the boundary, expect initially
discrete cells to quickly grow upscale into a line. Area at greatest
risk for severe storms is along and north of Highway 14, where an
SPC Day 2 Marginal Outlook (level 1 of 5) is forecasted.

These storms quickly blow through the available energy and begin to
weaken as the continue to the southeast into southwestern Minnesota
late Saturday night. As far as total rainfall is concerned, central
South Dakota will only see a few hundredths. As you move east the
totals increase to around a quarter of an inch as you approach the I-
29 corridor. As you move east into southwestern Minnesota a quarter
of an inch to nearly half an inch is possible.

SUNDAY-MONDAY: Very early Sunday morning, a post frontal rain band
will set up over western and central South Dakota. It will make its
way southeastward beginning around Chamberlain and moving southeast
along the Missouri River Valley. This band is expected to be light
and produce only an additional hundredth or two of rainfall.

The SPG tightens as the system continues to move southeast,
resulting in increased northwesterly surface winds for Sunday. Good
mixing Sunday afternoon up into the 30-35 kt LLJ will enhance wind
gusts to 25-30 mph east of I-29, and 30-35 mph for areas to the
west. Winds relax after sunset but remain breezy overnight with
gusts to 20 mph. Highs for Sunday will warm into the mid 70s.

By early Monday morning the low pressure system has settled over the
Great Lakes. One more shortwave will round the backside, bringing
chances for rain again Monday morning. This round will be focused
over southwestern Minnesota. Once again instability and shear will
be low, and so do not expect severe weather. Showers will move east
out of the region by around mid afternoon. Skies will begin to clear
from southwest to northeast and highs will reach the upper 60s in
southwest Minnesota, and low 70s elsewhere.

TUESDAY-END OF WEEK: We`re in for a pattern change beginning Tuesday
as a strong upper ridge build over the north central United States.
At the surface, high pressure, clear skies, and southerly winds will
result in a warm week ahead. From the upper 70s to low 80s Tuesday,
to the mid to upper 80s Wednesday and Thursday. Friday is slightly
cooler as a mid-level wave moves in and brings the next chances for
rain.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1250 PM CDT Fri Jun 6 2025

Mostly VFR conditions expected for this period. Isolated to
scattered light rain showers are possible this afternoon. Under
showers ceilings may decrease to MVFR status. While severe weather
is not expected, a few stronger showers could produce lightning and
wind gust to 40 mph. Near the end of the period KSUX may see
additional showers to thunderstorms. Again, severe is not expected.

Winds are light and variable, with minimal shear through 6000 ft
AGL. There is some weak instability present, and some weak funnels
have been reported. Funnels are possible through around 07.01Z.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...AJP