051
FXUS63 KFSD 181123
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
623 AM CDT Wed Jun 18 2025

.KEY MESSAGES...

- Patchy fog is possible across the area this morning. Should
  any fog develop, it will burn off during the morning hours.

- Another day of afternoon showers and storms is expected.
  Severe storms are not expected but a highly isolated heavy
  rainfall/flash flooding risk is possible.

- Severe storms may be possible Thursday night though details
  are uncertain regarding the location of potential storms.

- Confidence continues to increase in a heat wave coming for the
  end of this week. "Heat Risk" and "WBGT" categories rise into
  the "High" category Friday through Sunday. All outdoor events
  and activities should begin preparing now as headlines appear
  likely.

&&

.DISCUSSION...
Issued at 338 AM CDT Wed Jun 18 2025

Quiet conditions begin the day early this morning. This could change
over the next few hours though as clear skies and light winds could
allow for radiational fog to develop before sunrise. Will monitor
this potential for the rest of the night. Should any fog develop, it
will burn off during the morning hours. Today will be a rinse and
repeat of what we have seen over the past few days. Diurnally driven
showers and storms are expected to develop this afternoon before
weakening during the evening hours. Instability values remain more
on the monitor side with magnitudes less than 1,000 J/kg. Shear
remains weak so severe storms are not expected. However, with tall
skinny CAPE profiles in place, the potential exists for highly
isolated heavy rainfall/flash flooding to take place. This is due to
mean flow remaining at or below 20 knots which will keep storm
motions slow. Outside of rain chances, today`s high temperatures
will be a bit on the cool side as 850 mb temperatures only warm to
the mid teens aloft. Mixing these temperatures to the surface will
result in high temperatures into the upper 70s to low 80s. Low
temperatures will fall to the upper 50s to low 60s overnight.

Warm air advection (WAA) begins to strengthen on Thursday as upper
level flow takes on more of a westerly component aloft. This will
push 850 mb temperatures up into the 20s aloft. Mixing these
temperatures to the surface will result in hot high temperatures
from the 80s to low to mid 90s. The warmest temperatures will take
place along and west of I-29. While most of the day will be dry, WAA
will further strengthen as the low level jet (LLJ) ramps up during
the evening hours. This could lead to another evening and night of
showers and storms, some of which could be severe. While shear and
instability will be more than sufficient for severe weather, other
factors decrease confidence in this potential. While the nose of the
LLJ may be in the CWA, there is still some uncertainty where the
nose of the jet sets up. At the same time, BUFKIT soundings show
that little moisture will be in the layer of the jet, suggesting
that moisture could be a bit hard to come by even if instability is
still present when lifting from the nose of the jet. That said, the
GFS and NAM both show sufficient 850 mb moisture convergence which
could overcome this issue. The GFS, Euro, Canadian, and REFS all
show different probabilities for exceeding a tenth of an inch
Thursday night with the Euro having the highest probabilities up to
about a 50% chance while the REFS shows almost a 0% chance for the
same amount of rain. Given the lower confidence in the coverage and
location of storms, do agree with SPC`s marginal risk across the
area. Will be something to keep an eye going forward.

Upper level ridging begins to build aloft on Friday as warm air
advection remains strong. This will result in the beginning of the
heat wave for our area. The ensembles remain in decent agreement in
850 mb temperatures warming above 25C. In fact, the ensembles show
moderate to high probabilities up to a 50 to near 100% chance for
850 mb temperatures exceeding 25C. This will result in hot high
temperatures into the 90s to even low 100s across the Missouri
River. Dew points in the 60s to perhaps touching 70F will aid in
apparent temperatures reaching into the low to mid 100s. No break in
the heat overnight as lows look to bottom out in the 70s.

The heat continues through the weekend as the thermal ridge sits
over the Northern Plains. Saturday will be the warmest day with
highs again in the 90s to low 100s and heat indices in the upper 90s
to mid 100s. Sunday will be the "coolest" day of this heat wave as a
cold front begins to enter the forecast area. Highs on this day will
still be in the 90s to low 100s with similar heat indices. These
temperatures will result in a high Heat Risk and Wet Bulb Globe
Temperature being reached. Thus, heat headlines will likely be
needed. Rain chances could return to the area on Sunday from the
though this potential is a bit uncertain due to differences in the
fronts timing from the GFS, Canadian, and Euro.

While the front looks to push through the area on Monday, this could
result in continued chances for rain as the upper level jet shifts
to over the Northern Plains. In fact, medium range guidance is in
decent agreement in the right entrance of the upper level jet
remaining parked over the forecast area for the first half of next
week. Depending on how low level mesoscale details pan out, this
could result in a stormy start to next week. As of now, this
potential is supported by machine learning guidance so will keep an
eye on this potential next week. Aside from storm chances, high
temperatures will cool back to near seasonable thresholds as highs
look to warm to the 70s and 80s.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 623 AM CDT Wed Jun 18 2025

Shallow fog is present across a few locations this morning. Brief
reductions in visibility is possible within this shallow fog as a
few observations show visibilities down to MVFR levels. At the same
time, light rain showers along with a few thunderstorms are
currently along and west of the James River. While the shallow fog
burns off over the next few hours, these showers and storms will
drift eastwards throughout the day today. While confidence is high in
rain affecting KFSD and KSUX, confidence is not high enough to
include mention of thunder in their TAFs. Trends will be monitored
throughout the day. Any chance for rain will come to an end this
evening, leaving quiet conditions for the remainder of the TAF
period.

Winds begin today light and variable but will pick up out of the
north/northwest, with speeds up to 5 to 10 knots, and will slowly
back to out of the west/northwest by this evening.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...Meyers