270
FXUS63 KFSD 092323
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
623 PM CDT Sun Jun 9 2024

.KEY MESSAGES...

- Periodic chances for showers and storms return Monday night
  and continue off and on through much of the week.

- Uncertain severe weather risks focused mainly on Wednesday
  afternoon and evening.

- Temperatures rise above normal by the middle of the week.
  High probabilities (>80%) of highs above 80 degrees Wednesday
  and Thursday, with low-moderate (30-60%) probabilities of
  highs at or above 90 degrees for areas near/west of the James
  River Valley on Wednesday.

&&

.DISCUSSION...
Issued at 205 PM CDT Sun Jun 9 2024

TONIGHT-MONDAY: Surface high pressure sitting across our western
forecast area early this afternoon. Decent mixing east of the ridge
axis is allowing for moderate wind gusts, generally 15-25 mph though
slightly higher in our far east. As the ridge axis slides east this
evening and tonight, expect gusts to diminish quickly with loss of
heating as we approach sunset, followed by light & variable winds
through the overnight. The ridge axis shifts east of the forecast
area on Monday, allowing for some increase in south-southeast winds,
strongest along and west of the James River Valley where afternoon
gusts 25-30 mph are expected.

A bit of mid-high level moisture may produce high-based (near-above
10kft AGL) clouds at times but precipitation is not expected. High
temperatures look to be similar or slightly warmer than today, from
mid 70s to lower 80s most areas.

MONDAY NIGHT-TUESDAY: Mid-upper level trough and an associated cold
front will move east across the forecast area through this period.
Strong-severe storms are expected to develop across the High Plains
of western South Dakota mid-late afternoon Monday, with increasing
storm chances sliding east into central South Dakota through the
evening. As storms approach our western counties, most likely after
11/00Z, they will be encountering more stable air which is still
trying to recover from the departing surface ridge, and will be
stabilizing further with loss of daytime heating. If the storms in
western SD can develop strong enough cold pools to accelerate the
storms eastward into south central SD more quickly (as seen in 12Z
HRRR), could not rule out an isolated stronger wind gust. But given
the lack of instability/shear expected across our forecast area,
think the risk of severe weather is low.

Greater consensus among the CAMs is for showers/storms to decrease
in coverage as they encounter the more stable air across southeast
SD after sunset Monday evening, with scattered showers and a few non-
severe thunderstorms continuing east into southwest MN/northwest IA
through Tuesday morning before exiting off to the east by midday.
Tuesday should be a slightly warmer day than Monday, though in our
eastern areas this may depend on how quickly the lingering showers
and/or clouds move out. NBM highs for Tuesday may be a touch on the
warm side given low (10-30%) probabilities for temperatures topping
80F across the northeast half of the forecast area. However, given
uncertainty mentioned above, did not alter NBM highs significantly
at this point.

WEDNESDAY-THURSDAY: This looks to be the warmest period of this
forecast, especially Wednesday as a strong thermal ridge builds
north ahead of an approaching cold front. Ensembles are showing
better than an 80% chance of temperatures topping 80F across most of
the forecast area Wednesday afternoon. Low-moderate (30-60%)
probabilities for highs topping 90F are confined to our western
areas, along/west of the James River Valley, which is supported by
high (>80%) probabilities for 850mb temperatures exceeding 20C in
this area.

Similar high probabilities of 80+F persist across at least southern
parts of the forecast area for Thursday, though seeing more variance
among the different ensembles, leading to somewhat lower confidence.

This building of warmer air northward coincides with low level
moisture advection as well, with the broad ensemble showing moderate
(50-70%) probabilities for surface dew points rising above 65F by
late Wednesday (though only low 10-30% probabilities of exceeding
70F). The heat and humidity support moderate MLCAPE values of 1500-
2000J/kg seen in the deterministic models, which are consistent in
showing deep layer shear of 40+kt across the forecast area as well,
though the broader ensemble indicates low (10-30%) joint
probabilities of SBCAPE>1000J/kg and shear>40kt coincident with each
other. Timing of the mid-upper level shortwave may also throw some
uncertainty into the mix, as some deterministic models show the wave
moving through earlier in the day where it would not be able to take
advantage of peak heating. Thus still some uncertainty in severe
weather chances for Wednesday-Wednesday night, but will be a period
to monitor as we progress through the next few days.

As many or more questions regarding potential for Thursday, as
models vary in how far south the low level boundary will progress in
the wake of Wednesday`s activity. Shear remains moderate-strong with
mid-upper level jet across the northern Plains, but instability is
highly uncertain.

FRIDAY-SUNDAY: Low confidence in details for the outer periods of
the forecast, though trends seem to support seasonable temperatures
settling back into the region. Modest consensus showing a trough
sliding northeast across the region this weekend, perhaps favoring
Saturday-Saturday night for increased precipitation chances.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 622 PM CDT Sun Jun 9 2024

VFR conditions are forecast to prevail this TAF cycle. Should see
breezy N/NE winds quickly diminish near sunset, allowing light and
variable winds to persist overnight. Light winds continue tomorrow
morning, with direction becoming more southeasterly during the
afternoon. Otherwise, expect gusts between 15 to 25 MPH to be
possible by the end of the period along and west of the James
River.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...SST