450
FXUS63 KFSD 272355
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
655 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

- Rivers across the area have crested or are presently at crest.
  Expect rivers to slowly trend downward.

- Shower and storm chances remain in the forecast through Friday
  night. Strong to severe storms are possible later this evening
  and again Friday afternoon. More uncertainty exists with
  Friday`s threat.

- Although widespread heavy rainfall is not expected, isolated
  pockets of an inch or more are possible with thunderstorms
  tonight - with a worst case scenario of up to a localized 2".
  Otherwise, generally expect new rainfall amounts of 0.25" to
  0.50" through Friday night.

- Active pattern brings rain chances back to the region early
  next week. Locally heavy rainfall could be a threat, although
  confidence is low due to location/timing issues.

&&

.DISCUSSION...
Issued at 305 PM CDT Thu Jun 27 2024

A broad area of scattered showers continues across much of the CWA
this afternoon - this in association with midlevel warm air
advection in conjunction with a shortwave tracking over the region.
Rainfall amounts have generally been on the lighter side through the
day, though heavier showers over the northern James River Valley
have produced nearly an inch of rain at Huron. Latest CAMS have this
precipitation dwindling from west to east through the remainder of
the day as the upper level forcing drifts eastward.

Attention then turns to the potential for a few stronger to severe
storms for tonight. A surface low presently over eastern MT/WY will
slide into western SD by this evening, then into central SD during
the overnight hours. In the presence of MUCAPE around 2000 J/KG,
bulk shear of 40 to 50 kts, and midlevel lapse rates of 7 to 8 C/KM
over that area, strong to severe storms are expected to develop
through western/central SD by early this evening. These storms will
then push to the east through the early night time hours. As these
storms move into our area, they will become increasingly elevated
with soundings suggesting a deep cap in place over our area. This
would suggest that storms will weaken as they continue to move east -
eventually moving into a much more stable atmosphere east of the
James River. Even so, cannot completely rule out isolated severe
storms over south central SD and the James River Valley, generally
prior to midnight. With model PWATs running between 1.5" to 2",
there will be the potential for heavy rain with any stronger or more
persistent storms. A couple models - most notably the HRRR and NAM12
suggest a potential for 1 to 2 inches of rainfall from 00Z to 12Z on
Friday - although these models are not in agreement with the
placement of heaviest rainfall. In addition, other hi-res models do
not indicate this much rain overnight, and the 12Z HREF would
suggest only a 30-40% probability of receiving 1.5 inches of
rainfall overnight - focused over the northern James River Valley.
That being said, it will bear watching overnight. Southerly winds
will remain fairly breezy overnight with the approach of the
aforementioned frontal trough. Lows will be in the mid to upper 60s.

The surface low/frontal boundary pushes across the CWA on Friday,
exiting the area by late afternoon/early evening. Latest CAMs
suggest there could be shower and thunderstorm - generally east of
Interstate 29 in the mid to late afternoon. There will be another
potential for strong to severe storms over that area in the
afternoon with progged MUCAPE around 2000 J/KG - though midlevel
lapse rates will remain in the 6 to 7 C/KM range, and bulk shear
will only be moderate -running around 35 kts. In addition,
uncertainty remains how any earlier showers will impact the
potential for afternoon convection. The potential for heavy rain
looks to be lower on Friday, though higher amounts would of course
be possible in a heavier storm. It will be a warm day with highs in
the upper 70s to lower 80s. A few light showers may linger even into
Friday night, though rainfall amounts would be very light.

With the passage of this system, a nice weekend is in store as a
surface ridge builds into the region through the period. With that
will come below normal temperatures with highs only in the 70s and
lows in the 50s.

Rainfall chances return to the area by the beginning of next week as
an upper level trough swings through the Northern Plains and
moisture returns on a southerly low level flow for Monday into
Tuesday. Cannot rule out the potential for heavy rain for portions
of the area by Monday with model PWAT values of 1.5" to 2"+. With
that could also come the potential for severe weather as outlined by
SPC Day 5 convective outlook. There looks to be a warming trend
through the middle of the week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 655 PM CDT Thu Jun 27 2024

Scattered showers/thunderstorms will impact the area through
this TAF period, though with low confidence in exact timing and
location of greater thunderstorm chances, will have only limited
mention of TS in the TAFs. Aside from ongoing activity near KFSD
at the start of this period, the most favored area for storms
appears to be near KHON during this overnight.

Aside from an uncertain thunder threat, will see a potential
for MVFR ceilings Friday morning ahead of a cool front pushing
east. This front may trigger additional showers/storms by Friday
afternoon, mainly east of the I-29 corridor. Front will also
bring a wind shift from south-southeast to northwest.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...JH