080
FXUS63 KFSD 261955
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
255 PM CDT Sat Apr 26 2025

.KEY MESSAGES...

- Showers and very isolated thunderstorms continue to move
  northeast through tonight. Additional rainfall amounts
  generally a tenth of an inch or less.

- Elevated instability could lead to severe weather and locally
  heavy rain Sunday night into early Monday morning. The best
  chance for development appears to be from about 10 PM to 5 AM
  Sunday night into Monday morning across western South Dakota,
  possibly moving northeast into our area after midnight.

- Overall mid morning Monday into mid afternoon should be a lull
  in activity. Strong to severe storms may develop along a
  surface front over southwestern Minnesota and northwestern
  Iowa by late afternoon into the evening, with guidance slowing
  down the timing of the front by a couple of hours. Greatest
  severe risk is 4 to 9 PM along and east of I-29.

- Next better chance for showers and thunderstorms will be
  Wednesday/Thursday of next week.

&&

.DISCUSSION...
Issued at 254 PM CDT Sat Apr 26 2025

NOW-SUNDAY: Chilly and breezy today across the area, with
southeasterly wind gusts to 35 mph and temperatures in the 50s to
lower 60s. An area of showers and very isolated storms driven by
increasing WAA and elevated instability are moving east-northeast
across northern NE into the MO River Valley this afternoon. So far,
rainfall amounts have been around 0.10" or less across northern NE.

Showers and very isolated thunderstorms continue to move to the
northeast through tonight, thanks to continued WAA, LLJ, and a weak
wave moving through the forecast area. Rainfall amounts are expected
to remain light this evening and tonight as we struggle at times
with a dry subcloud layer - so could see an additional tenth of an
inch or so. Lows tonight fall into mid 40s to near 50.

Low level moisture increases late tonight through Sunday as
southeasterly flow increases ahead of the deepening low pressure and
ejecting trough , allowing for stratus to develop over the region.
This lower cloud deck will help keep temperatures cooler than our
mixing potential with highs in the mid 60s to lower 70s. Additionally,
any showers/sprinkles will likely struggle due to lack of instability
in the moist layer. Expect breezy southeasterly winds to continue,
with gusts to 30 mph.

SUNDAY NIGHT-EARLY MONDAY: First short wave and upper level jet
streak eject into the NE Panhandle/western SD through the evening
hours Sunday. With elevated instability 1500 J/kg or more and mid
level lapse rates over 7.5 deg C/km, storms which develop in this
area could be strong to severe and remain so as they move east-
northeast. CAMs and other deterministic 12z guidance have trended
these features a bit further to the west and an hour or two slower.
So although an isolated strong to severe storm is possible late
Sunday night into Monday morning (risk timing for our area after
midnight through about 6 AM), the greater risk will across western
and north central SD earlier in the night. Large hail and damaging
winds are the main threat. Thunderstorms could produce locally heavy
rainfall with PWAT values near/above an inch.

Lows in the 50s with continued breezy southeasterly winds.

MONDAY-MONDAY NIGHT: Expect a lull in rain and storms for a brief
period of time from roughly mid Monday morning to mid Monday
afternoon for most of the area as the morning convection lifts off
and ahead of the potential development along the front. As with the
previous forecast, there remains some uncertainty in the timing of
the front, with the Canadian the slowest of the models by 6 hours or
so. The NAM is still lagging a bit from the GFS/ECMWF, although not
as much as previous. By Monday afternoon, surface low should be
somewhere over northeastern SD, with attendant cold front stretching
southwest into KS. Looking aloft, mid level vort max and upper level
jet streak are just west of the surface front. WAA and southerly
flow ahead of the front will allow for moisture (and instability) to
increase with temperatures in the 70s and 80s.

With guidance slowing down a touch with the front, believe the
greatest severe threat will be along and east of I-29 from roughly 4
PM to 9 PM. All modes of severe weather are possible; however, large
hail and damaging winds will be the main threats. Bulk shear values
exceed 60 knots with the LLJ in place. As mentioned already,
southeasterly flow aids in efficient moisture return and well above
average temperatures provide ample instability with 1750-2000+ J/kg
of MUCAPE. Mid level lapse rates are above 8 deg C/km. A tornado
can`t be ruled out given strong 0-1 km shear, especially if a storm
develops near a boundary and is surface based. Storms may produce
locally heavy rainfall with PWATs again around 1 inch.

Sharp CAA behind the front/convection Monday night will lead to
breezy northwesterly winds overnight and into Tuesday morning with
gusts to 30 mph. Lows in the mid 30s to lower 40s.

TUESDAY ONWARD: With the main mid/upper level trough moving to the
east early Tuesday and surface high pressure sliding in, anticipate
Tuesday to be relatively cooler and dry. A couple of mid level short
waves and upper level trough swing through the northern and central
Plains mid week, which could bring some light rain chances back to
the region - with chances for more than a tenth of an inch less than
30%. Ridging and surface high pressure move in again to end next
week. Temps remain above normal from Wednesday through the end of
the week with highs largely in the 70s and lows in the 40s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1251 PM CDT Sat Apr 26 2025

Scattered showers over south-central South Dakota and northern
Nebraska will continue moving towards the I-29 corridor through the
early afternoon. Can`t rule out isolated rumbles of thunder, but
chances are not high enough to warrant mention in the TAFs. These
showers will exit off to the north and east this evening, but a deck
of MVFR stratus will creep into our area from west to east late
tonight through Sunday morning. These clouds may drop into IFR at
times from KSUX to KFSD in the last couple of hours of the period,
but confidence was not high enough to put in the TAFs at this time.

Winds will stay breezy and mainly out of the southeast across the
area through the rest of today into tomorrow morning. Gusts will
begin to pick up further into the 25-30 kt range to close out the
period.

&&

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

&&

$$

DISCUSSION...SG
AVIATION...Samet