565
FXUS63 KFSD 242100
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
400 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- River Crests have already occurred or will occur within the
  next 24-48 hours. While no significant amounts of rainfall
  will occur, areal flooding caused by the prior excessive
  rainfall continues across portions of the area.

- The hot and humid conditions will continue through this
  evening with heat indices up to 110 degrees possible across
  the area. Parts of the Heat advisory have been upgraded to an
  Excessive Heat Warning.

- A highly conditional severe weather risk continues this
  afternoon and evening. However, if thunderstorms can develop;
  a favorable atmosphere would help them intensify quickly.

- While significant precipitation is not expected, an active
  pattern aloft will help bring multiple rain chances through
  the area throughout the week.

&&

.DISCUSSION...
Issued at 352 PM CDT Mon Jun 24 2024

REST OF THE AFTERNOON/EVENING: A hot and humid day continues! Taking
a look across the area, 18z observations currently have us sitting
in the upper 80s to lower 90s with dew points closer to the upper
60s to low 70s. With southerly to southwesterly winds firmly in
place and heat continuing to build; expect conditions to become
increasingly muggy as dew points increase towards the low to mid 70s
for the day. As temperatures peak in the upper 80s to mid 90s this
evening, our heat indices will likely follow suit with values up to
110 degrees expected by the late afternoon with the warmest
conditions expected south of Hwy-18. As a result, a heat advisory
remains in effect through 8 pm CDT for most of the area. With some
observations along the Hwy-20 corridor and lower Missouri River
Valley trending towards 110 degrees, decided to upgrade portions of
northwestern IA, far southeastern SD, and far northeastern NE into
an Excessive Heat Warning through 8 PM CDT. Lastly, while widespread
heat index values of up to 110 degrees are not expected; there
is some low potential (<20%) for areas not outlined in the
previously mentioned warning to approach criteria for an hour or
two at most.

Shifting gears to our precipitation chances, scattered showers have
begun to develop ahead of weak mid-level wave and its associated
cold front. As this cold front continues to drift to the southeast,
some gradual development will be possible, but our severe weather
chances continue to look rather limited this afternoon and evening.
Looking at the set up, peak heating along with an influx of warm and
moist air ahead of the near surface boundary will help instability
values increase to 4000-6000 J/kg at the mixed level with 30-40 kts
of deep layer shear expected due to an increase LLJ. This combined
with DCAPE values up to 1000 J/kg and mid-level lapse rates up to 9
degree c/km in the hail growth zone will make for an ideal
environment for large to giant hail up to 2 inches (Hen Egg Size)
and damaging winds up to 70 mph with any developing activity.
However, with most model derived soundings showing the presence of
strong cap and dry air in the lower levels of the atmosphere; its
going to be very hard for any developing updrafts to reach their
full potential given the conditions. As a result, confidence
continues to lower in the potential for severe weather tonight.
With this in mind, the likely scenario is scattered showers with
a few isolated thunderstorms mostly east of I-29 with
accumulations expected to fairly limited.

Tonight: Looking into tonight, winds will become more
northwesterly behind the previously mentioned cold front this
evening before decreasing after sunset. Temperatures will remain
rather elevated due to lingering WAA. As a result, lows are
only expected to drop into the upper 60s to low 70s for the
night. Looking aloft, a subtle mid-level wave will quickly pass
through parts of the area late tonight bringing some weak
isentropic lift. With this in mind, will likely see a few
scattered showers develop from about 06z onwards with a few
rumbles of thunder possible. This activity should gradually
spread eastwards towards daybreak Tuesday morning before things
scoot our of our area by late morning.

TUESDAY: By Tuesday, northerly to northwesterly surface flow
along with increasing cold air advection (CAA) behind the
previously mentioned front will lead to a sharp decrease in
temperatures for Tuesday with the resulting highs being the low
to upper 80s and low 90s. Shifting gears to our next
precipitation chances, a few isolated showers and thunderstorms
could develop along the Missouri River Valley and Hwy-20
corridors by Tuesday afternoon and evening with a few
potentially becoming severe. However, depending on where the
cold front eventually stalls out; the better corridor of
instability will likely follow. With this in mind, most
deterministic guidance now has this near-surface feature
stalling south of the Hwy-20 corridor closer to I-80. As a
result, pattern recognition tells me that most of the stronger
activity will likely stay just to our south with us likely
getting a few remnant showers with an isolated thunderstorm or
two. Either way, SPC now has areas along the Hwy-20 corridor
outlined in a Day 2 Slight Risk (Level 2 of 5) due to the
severe weather potential.

WEDNESDAY-SUNDAY: From the midweek into the weekend, a particularly
active pattern aloft will lead to increased rain chances from
Wednesday night into Thursday morning and again Thursday
afternoon into Friday as multiple mid-level waves and
potentially a surface low swing through the region. Since there
are timing and intensity differences among deterministic
guidance, a bit of uncertainty continues with exact amounts and
thus the severe weather potential. Nonetheless, ensemble
guidance now shows low to medium confidence (20%-40%) in up to
half an inch of QPF though Friday. Lastly, after near normal
temperatures on Friday; our temperatures should noticeably
decrease through Sunday with highs expected to peak in the mid
to upper 70s for the day.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1237 PM CDT Mon Jun 24 2024

VFR conditions will continue for the duration of the TAF
period. Taking a look at satellite imagery, a few scattered
showers continue to develop ahead of a cold front west of I-29
this afternoon. As this front drifts to the southeast, expect
some gradual development. However, accumulations should be
fairly limited. Otherwise, breezy southerly to southwesterly
winds ahead of the front will become more northwesterly behind
the front this evening. Winds should gradually diminish after
sunset with a few more light showers possible nearly daybreak
along the Hwy-14 corridor to end the TAF period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 8 PM CDT this evening for SDZ038>040-050-
     052>068.
     Excessive Heat Warning until 8 PM CDT this evening for
     SDZ069>071.
MN...Heat Advisory until 8 PM CDT this evening for MNZ071-072-080-
     081-089-090-097-098.
IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003-
     012>014.
     Excessive Heat Warning until 8 PM CDT this evening for
     IAZ020>022-031-032.
NE...Excessive Heat Warning until 8 PM CDT this evening for NEZ013-
     014.

&&

$$

DISCUSSION...Gumbs
AVIATION...Gumbs