666
FXUS63 KFSD 200345
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1045 PM CDT Sat Apr 19 2025

.KEY MESSAGES...

- A pleasant evening is ahead.

- Rain returns to the area on Sunday, with the best chances
  residing east of I-29. A quarter to a half an inch of rain is
  likely, with higher totals farther east.

- Temperatures look to be seasonable to seasonably warm for
  most of next week. Chances for rain continue throughout the
  week but details are uncertain at this time.

&&

.DISCUSSION...
Issued at 225 PM CDT Sat Apr 19 2025

THIS AFTERNOON/EVENING: A pleasant afternoon followed by a pleasant
evening today. Deterministic models have held afternoon surface
highs steady from the previous forecast. As our winds turn westerly
to southwesterly this afternoon, 850 mb temps warm to 2-4 deg C. At
the surface we can expect highs in the mid 50s to low 60s. Overnight
lows will dip into the mid to upper 30s.

Looking aloft a deep, positively tilted trough has closed off, and a
surface low pressure has developed over the Four Corners region.
Tonight, that surface low is expected to eject out onto the southern
Plains and accelerate northeastward. As it does so, the midlevel
wave takes on a negative tilt, indicative of strengthening.

SUNDAY: The main surface low pressure looks to move past our region
to the southeast. However, we will still see some rain from this
system as we experience a strong northward surge of WAA. This with
frontogenetic banding in the 700-600 mb level will trigger
showers as moisture wraps around the low. Most guidance
indicates these showers will be confined along and east of I-29,
which is the most likely solution. However, the 12Z run of the
GFS has light showers pushing as far west as the James River
Valley. So will keeps some very low PoPs in that area. As you
move east, PoPs increase with the highest chance for rain (>60%)
east of a line from Sioux City to Tracey Minnesota. While
strong storms are not expected, some very weak instability in
the mid levels may result in a few rumbles of thunder. While
most areas that see rain will be light, areas under the
frontogenetic bands may see brief periods of heavier rainfall.
This is again most likely east of the Sioux City to Tracey line.
Rainfall totals will range from a few sprinkles to a couple
hundredths west of I-29, and 0.25-0.5 inches east. Ensembles
tend to support this with a 60-80% probability of 0.25 inches or
more. Higher totals approaching 0.75 inches are possible east
of a line from Sloan to Spirit Lake. However, ensemble
probabilities drop off to less than 50%. A note on rain totals:
If this system wobbles to the west or east it could have a large
impact on rain totals. A wobble west could mean higher, and to
the east lower. Highs for Sunday will depend on how much cloud
cover an area experiences, and whether or not it rains and
evaporative cooling takes place. In general, west of the James
River will see highs in the low 60s, and east will see 50s.
Sunday night lows will be in the 30s.

MONDAY-TUESDAY: Rains showers move east early Monday morning, and
clouds will clear. Light northerly winds will become southerly and
slightly breezy. WAA in the 850 mb layer boosts temperatures
there into the 4-8 Deg C range. Mixing down to the surface we
can expect highs in the 60s to low 70s. By Monday evening, a
mid-to-upper level shortwave and associated surface low will
push into the area from the west. We will find ourselves in the
warm sector with strong WAA triggering light showers early
Tuesday morning. A band of 750-700 mb frontogenesis with around
500 J/kg of MUCAPE may be enough to trigger some thunderstorms.
Lapse rates are conditionally stable, between 7 and 8 degrees
C/km. This set up may allow for a few stronger thunderstorms
that may contain small hail and gusty winds. Enough differences
in guidance exists that confidence in stronger storms is low at
this point. Showers clear out by Tuesday afternoon and skies
clear. Highs will reach the 70s and lows will fall to the 40s.

WEDNESDAY-AND-BEYOND: Mostly zonal flow aloft for Wednesday will
keep conditions pleasant, with highs in the 60s-70s and lows in the
40s. Beginning Thursday a series of short waves and ridges will pass
through the region, bringing periodic chances for rain. Highs will
be average to seasonably warm, in the mid to upper 60s.

NOTE ON FIRE CONDITIONS: Grassland fire danger will generally be in
the moderate to high category for the upcoming week. With
periodically breezy winds, and relative humidity levels dropping to
near critical to critical levels at times, fire is still a concern.
Please continue to be cautious with sources of ignition such as
cigarettes, dragging chains, hot brakes, and hot exhausts.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1040 PM CDT Sat Apr 19 2025

Southeasterly winds of 5 to 10 kts tonight will increase to 10
to 15 kts on Sunday, gusting near 20 kts through Sunday
afternoon and evening. Rain showers are expected to develop
through areas primarily east of the Interstate 29 corridor on
Sunday afternoon. With that, ceilings and visibilities will
decrease into the MVFR/IFR range. Showers begin to pull to the
east after 03Z on Sunday night, though MVFR/IFR ceilings will
persist through the remainder of the TAF period.

&&

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

&&

$$

DISCUSSION...AJP
AVIATION...JM