258
FXUS63 KFSD 121641
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1141 AM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Wildfire smoke continues to stream overhead through the
  weekend into early next week. However, surface impacts are
  currently not expected.

- 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 HREF ensembles would indicate a
high probability (70-100%) of reaching heat advisory criteria on
Saturday - with the GEFS/ECMWF/Canadian ensembles reaching only
a moderate probability (40-50%), though there is a higher
probability (50-70%) in that suite 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 /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1140 AM CDT Fri Jul 12 2024

VFR conditions prevail through the period. Southeasterly winds
gust around 20 to 25 knots this afternoon, with gusts dropping
off after sunset. Winds will be light overnight, but think
they`ll be just strong enough to preclude fog development.
Southerly winds around 10 knots expected into tomorrow
afternoon.

&&

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

&&

$$

DISCUSSION...JM
AVIATION...SG