457
FXUS63 KFSD 120832
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
332 AM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Isolated storms will be possible west of Interstate 29 through
  mid morning. Severe chances are low.

- Wildfire smoke continues to stream overhead. Smoke should
  track east as the upper ridge builds in through the weekend.

- Showers and thunderstorm chances look to be lowering for this
  weekend.

- Temperatures and dew points increase through the weekend.
  Moderate to high (50-70%) chance of seeing heat indices above
  100 degrees on Saturday and Sunday afternoon for portions of
  the area.

&&

.DISCUSSION...
Issued at 330 AM CDT Fri Jul 12 2024

Currently quiet across the region, with the only convection of note
(isolated) residing over western and central NE. There are still a
couple of hi-res models (NAMNest/ARW) that want to initiate
elevated thunderstorms west of Interstate 29 after 10Z, though
confidence in this scenario is low with soundings indicating
capping up to 700 mb or higher and dry air residing below this
level. If a storm were to develop, anticipate that it would
remain sub severe with MUCAPE running around 1000 J/KG and
effective bulk shear on the weaker side - around 20 kts. If any
activity does develop, it should dissipate shortly after 15Z.
Otherwise, an upper level ridge over the western CONUS builds
slightly eastward today, while at the surface, a ridge remains
entrenched over the western Great Lakes/OH Valley region. This
will provide a continuing southerly flow to our area, as an 850
mb thermal ridge to our west begins to nudge eastward. This will
result in slightly warmer day - most notable over the James
River Valley and westward. Look for highs in the mid 80s to
lower 90s. In addition, with increasing low level moisture, dew
points will rise into the upper 60s to lower 70s by afternoon.
This will yield a little more relative humidity as afternoon
heat indices climb to the upper 80s to mid 90s. Latest smoke
models show smoke continuing to stream overhead during the day,
which could result in hazy skies.

Still seeing model differences in regard to any potential convection
late tonight. The HRRR and NAMNest develop thunderstorms over east
central SD/southwestern MN toward 12Z on Saturday as another
shortwave tracks through the region, though other models keep it
dry. In light of that, kept only low end pops (20%) over that area.
It will be a mild night with lows in the upper 60s to lower 70s.

Attention then turns to the increasing heat for Saturday and Sunday
as the aforementioned upper level ridge exerts more influence on our
area. 850 mb temperatures rise into the mid to upper 20s C on those
days, with ensembles showing 700/850 mb temperatures in the 90th or
greater percentile with respect to climatology. This will play out
to highs well into the 90s, and with increasing dew points into the
lower to mid 70s, heat indices on Saturday and Sunday afternoon will
reach 95 to 105 degrees. Latest ensembles would indicate only a
moderate probability (40-50%) of reaching heat advisory criteria for
Saturday, though there is a higher probability (50-70%) on Sunday.
In light of that, some sort of heat headline will most likely be
needed for portions of the area during that time frame. In terms of
thunderstorm chances through the period, most recent models keep it
primarily dry both Saturday and Sunday - which seems reasonable
considering an extremely capped atmosphere as a result of the very
warm temperatures.

For the beginning into the middle of next week, there looks to be a
cooling trend through the period as the upper level ridge breaks
down over our area, as influence is felt by an upper level trough
that dives into the Northern Plains and upper midwest through the
period. After another warm day on Monday (mid 80s to lower 90s),
temperatures fall back to below normal levels for Tuesday through
Thursday. While there may be periodic low precipitation chances
during the period, confidence in coverage and timing is low with
model differences.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1018 PM CDT Thu Jul 11 2024

VFR conditions continue early into the overnight hours, however
mid-lvl clouds will begin to develop west of the James River and
into the Missouri River valley after midnight. Most short term
model guidance indicated scattered elevated thunderstorm
development by 04Z west of the James River that may continue
into mid-morning. Given the uncertainty on areas of development
and coverage will leave out of current HON forecast.

Further east, some patchy fog may again be possible as a thick
smoke plume remains overnight.

Friday will see a continuation of scattered mid-lvl clouds, high
level smoke, and afternoon CU. Winds will increase from the SSE
through the daytime hours gusting over 20 knots at times.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...Dux