560
FXUS63 KFSD 271144
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
644 AM 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 today and
  again Friday. 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.
  Otherwise, generally expect new rainfall amounts of 0.25" to
  0.50" through Friday night, although amounts of 0.50" to 1"
  are possible.

- 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 341 AM CDT Thu Jun 27 2024

CURRENTS: Scattered showers and isolated storms across the region
this morning. Most of our area has stayed dry so far (through 3 AM)
outside of a 0.01" of rain at Sioux City. With dry sub cloud layer,
expect precip this morning to remain light if it is able to reach
the ground at all. Exception would be with any thunderstorms,
although so far the highest total was Pierre with a tenth of an inch
in an hour with showers/thunderstorm in the area. Otherwise, mid
level clouds are on the increase. It`s a pleasant morning with temps
in the upper 50s to upper 60s.

TODAY THROUGH FRIDAY NIGHT: Showers and very isolated storms this
morning continue to move east with the WAA and initial piece of mid
level forcing. Severe weather is not expect with any of this initial
activity, as instability remains around 100 J/kg or less. Cloud
cover and limited mixing today keeps temperatures again on the cool
side, with highs this afternoon in the 70s to near 80. Winds
increase today as the surface pressure gradient tightens with lee
side cyclogenesis and the low moving into western SD. Strongest
south to southeast winds early in the day are expected west of I-29
with sustained winds around 15-20 mph and gusts to 35 mph. These
breezy winds move east through the overnight hours. Surface low
pressure and attendant cold front move east this evening and
overnight into central SD, ahead of the main mid/upper trough axis.
Near and ahead of this front is where attention turns to this
afternoon and evening for potential strong to severe storms.
Instability is expected to increase quickly in the warm sector, with
CAPE values (depending on the layer sampled) more than 2000 J/kg.
Bulk shear across western/central SD over 35 knots and steepening
mid level lapse rates over near 8 deg C/km are also supportive of
strong to severe storms. Main threats would be large hail to ping
pong ball size (1.5") and wind gusts of 70 mph. A tornado or two are
possible for any storm more surface based than elevated (or closer
to the front) with low LCL heights. Big caveat for tonight`s severe
threat - storms will be moving into a much more capped (stable)
environment especially past the MO River - so not sure if/how long
they would be able to either remain severe in our area or sustain
themselves in general. Storms may be more linear in nature on
approach of our forecast area, but with lower 0-3 km bulk shear,
they may not be able to sustain themselves (in addition to the
aforementioned cap). Outside of this activity, some additional
scattered showers/storms are expected overnight. Lows tonight in the
mid/upper 60s.

Front tracks across the forecast area Friday, with our breezy winds
switching from south/southeast ahead of the front to northwest once
it passes. Highs Friday in the upper 70s to mid 80s. Uncertainty
exists with the severe chances during the afternoon and into Friday
night due to some uncertainties including: how today/tonight`s
convective evolution plays out, where the surface cold front and
mid/upper level support end up, and atmosphere recovery. However, if
strong/severe storms can develop, greatest risk looks to be east of
I-29. Although shear and lapse rates are progged to be slightly
lower than today/tonight, all modes of severe weather are in play
(ping pong ball sized hail, wind gusts to 70 mph, and a tornado or
two are possible). Showers and storms decrease through the overnight
hours Friday into Saturday, with lows in the upper 50s to mid 60s.

Locally heavy rain is possible with any thunderstorm through Friday
night with more efficient moisture transport, increasing PWAT
values, and deep warm cloud layers. Through Friday night, new
rainfall amounts generally remain near 0.25" to 0.50". A few
locations could see around 0.75" if multiple periods of showers
occur. HREF guidance shows that most rainfall rates would be around
0.25" per hour or less through tomorrow night, with very isolated
and low (< 20%) chance of more than 1" of QPF per hour. Again,
widespread heavy rain is not expected.

SATURDAY ONWARD: CAA and mid level westerly flow prevail on
Saturday, bringing a cool and pleasant day to the region. The next
very quick moving short wave tracks through the mid level pattern
Sunday, which could bring some very light rain to the area as
surface high pressure slides off to the east. Cooler than average
temps prevail Sunday as well. Highs in the 70s to lower 80s and lows
in the 50s.

Confidence is low given the uncertainty in the details, but locally
heavy rain is possible early next week as a couple of mid level
waves and troughs swing through the northern and central Plains.
Increased moisture return, deep warm layer moisture, and PWATs 1.5"
to 2"+ would support this, but again, confidence is low in exact
location/amounts. Temperatures early to mid next week will be near
to below average on Monday, and near/above average into at least mid
next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 636 AM CDT Thu Jun 27 2024

Very uncertain TAF forecast for this period due to periods of
showers and thunderstorms. MVFR to IFR conditions are expected
with showers and storms. Some storms this afternoon and evening
could become strong to severe with large hail and damaging winds
the main threats (greatest risk west of the James River). Period
of showers and storms will continue overnight, with lower
confidence in timing/coverage later in the period.

Outside of convection, southeasterly winds will be breezy with
gusts around 25 to 30 knots. Have added LLWS for KFSD/KSUX and
surrounding areas late tonight - mainly due to increasing and
shifting LLJ. Winds west of the James River will begin to shift
more toward to the west by the very end of the period behind a
cold front.

&&

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

&&

$$

DISCUSSION...SG
AVIATION...SG