830
FXUS63 KFSD 170924
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
424 AM CDT Fri May 17 2024

.KEY MESSAGES...

- Well above normal temperatures will end the work week. High
  confidence (90%) in widespread highs in the mid-upper 80s
  today, with low-moderate confidence (30-50%) in some areas
  topping 90F west of I-29.

- Periods of breezy conditions return today and continue
  through the weekend. Occasional gusts over 30 mph this
  afternoon into Saturday, but probability of reaching Wind
  Advisory criteria is low.

- Sunday afternoon into Tuesday continues to look more active
  with the potential for periods of locally heavy rain and
  severe weather possible.

&&

.DISCUSSION...
Issued at 423 AM CDT Fri May 17 2024

TODAY-SATURDAY: Broad warm advection early this morning has been
producing mid-level clouds, with isolated high-based sprinkles
sliding southeast. Have even seen a few lightning strikes in our
southwest in an area of steeper mid-level lapse rates. Expect this
activity to continue to drift southeast across the forecast area
through mid-morning before waning as warm advection diminishes by
15Z. Focus for the rest of today will be breezy south winds and
brief push of well above normal temperatures as a low level thermal
ridge builds into central SD. 850mb climbing above 20C by this
afternoon could support a few highs above 90F west of I-29, while
mid-upper 80s will be more common across the east. Strongest low
level winds are focused east of the thermal ridge, with soundings
supporting occasional gusts to around 30 mph across portions of
northwest IA/southwest MN this afternoon.

35-40kt low level jet continues overnight, with another surge of
broad warm advection ahead of an approaching cold front. Moisture
profile is a little drier tonight than we are seeing early this
morning, but with some weak mid-level instability cannot rule out
some spotty sprinkles once again, so have added a mention of this
ahead of the front tonight into early Saturday. This looks to be
about the only precipitation chances with this front, which should
push east of the forecast area before midday Saturday. Strong push
of cold advection behind the front could result in a brief period of
stronger winds early Saturday across our west, with some soundings
showing initial post-frontal mixing tapping into 40kt atop the mixed
layer. This looks to be short-lived, though, with 30-35 mph gusts
more likely in the post-frontal air mass Saturday morning, and this
mainly west of I-29. As we progress through the day, a slackening
pressure gradient should lead to less breezy winds through the
afternoon, with light/variable winds Saturday night as surface high
pressure slides across the area. Highs on Saturday are still a
little uncertain, though with better consensus on frontal timing,
think the potential for highs topping 80F is on the low side, even
in our far southeast.

SUNDAY-TUESDAY: Much more unsettled period as we head into next
week. Sunday will see increasing rain chances in response to a
couple of mid level waves moving across the region in southwest flow
aloft. First wave moves through Sunday morning, combined with a
broad area of warm advection. This wave will be fighting some
lingering low-mid level dry air in the wake of departing surface
high pressure, but would expect to see at least scattered showers
and a few embedded thunderstorms as the deep lift works to overcome
the dry air. A trailing wave is progged to slide across the area
during the afternoon/evening, though some questions regarding the
ability to destabilize in the wake of morning activity. If the
instability materializes, seeing fair agreement among models that
deep layer shear will be supportive of a few organized strong to
severe storms. Cannot argue with latest SPC Day 3 Marginal Risk
(Level 1 of 5) in our southern counties, generally south of the
Highway 18 corridor, though still plenty of uncertainty regarding
timing/location of more favored severe threat.

We remain in the somewhat active southwest flow through Tuesday,
though ensemble joint probabilities of sufficient instability/shear
remain on the low side (<30%) for Monday through Tuesday. If the
surface boundary remains to our south as projected by some model
solutions, this could limit our severe potential but may increase
the potential for areas of heavy rainfall as a stronger wave later
Monday night-Tuesday slides northeast along the elevated boundary.
All in all, uncertainty is high regarding how exactly things will
evolve through the first half of next week. However, ensembles are
showing moderate probabilities (50-70%) for total rainfall topping
1" through Tuesday night, with low (20-30%) probabilities for over
2", both focused across the southeast half of the forecast area
where rivers have already been running higher. WPC highlights this
areas with a Marginal (Level 1 of 4) Risk in the Days 3 through 5
(Sunday through Tuesday) excessive rainfall outlooks.

WEDNESDAY-THURSDAY: Details for this period are low confidence as
there is little agreement among the longer range models. However,
moderate consensus in some cooler air settling into the northern
Plains mid-week with periodic rain chances possible, depending on
how quickly a deepening upper low retreats to the northeast.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1035 PM CDT Thu May 16 2024

VFR conditions expected through the TAF period. Light southerly
winds overnight will increase by Friday morning, gusting around
20 kts through Friday evening. As winds increase aloft on
Friday evening, LLWS will develop at all TAF sites.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...JM