034
FXUS63 KFSD 191717
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1217 PM CDT Thu Jun 19 2025

.KEY MESSAGES...

- Isolated storms are possible mainly late evening and
  overnight. If storms develop, they could be strong to severe.
  Better chances in southwest MN and northwest IA near and east
  of the Buffalo Ridge.

- The end of the week heat wave remains on track. Dangerous heat
  is likely Friday through Sunday with heat indices spanning
  from the upper 90s to the 100s during this period of time.
  Please make sure to stay hydrated and limit prolonged outdoor
  activities where possible.

- Confidence is beginning to increase in heavy rainfall
  potential returning to the region next week. Details are still
  uncertain so continue to monitor the latest forecast for the
  most up to date information.

&&

.DISCUSSION...
Issued at 402 AM CDT Thu Jun 19 2025

Quiet conditions begin the day today with light and variable winds
and mainly clear skies. Winds will begin to strengthen a bit as
mixing increases this morning. However, winds will further
strengthen this afternoon out of the south/southwest with gusts up
to 25-30 mph as mid level winds begin to increase aloft. 850 mb
temperatures will warm to the low to mid 20s which will result in
above average high temperatures up to the upper 80s to mid 90s. The
warmest temperatures will occur along and west of the James River.
While forcing for ascent will be negligible through the afternoon
hours, BUFKIT soundings suggest that locations west of the James
River may reach convective temperatures which could result in an
isolated storm forming. While the probability of this is low (~20%
chance), still can`t rule it out completely despite a weaker cap in
place. Should a storm form, it could be strong to severe given that
ample buoyancy will be in place with CAPE values up to 1,000 to
1,500 J/kg and deep layer shear will have a magnitude of about 40 to
45 knots. Storm chances could increase this evening and night as the
low level jet (LLJ) ramps up. However, the best chances for storms
looks to be north and east of the forecast area where the nose of
the LLJ will lie. Still have left chance PoPs in place in the event
that the LLJ is able to get a storm to develop within the warm
advective regime despite lacking moisture in and around 850 mb.
Overnight temperatures will fall to the 60s and 70s.

The anticipated heat wave begins on Friday as the thermal ridge
begins to push into the Northern Plains from the front range of the
Rockies. 850 mb temperatures will warm to the mid 20s to up to about
30C aloft. Mixing these temperatures to the surface will result in
hot high temperatures into the 90s to 100s, warmest along the
Missouri River Valley and along and west of the James River. At the
same time, dew points will moisten up to the 60s and 70s. This will
result in heat indices reaching up to 100 to about 110F Friday
afternoon. Southerly winds will again be breezy across the area with
gusts up to about 35 mph expected which could help temper the heat
and humidity just a bit. A large cap will be in place on Friday
which will keep any rain and storm chances at bay. Any chance for
storms will come Friday night but it will be well north of the
forecast area where the best forcing for ascent will lie. With high
dew points in place, overnight low temperatures will only fall to
the 70s.

The hottest day of this heat wave will come on Saturday as the
thermal ridge advects right over the forecast area. 850 mb
temperatures will further warm to the upper 20s to low 30s aloft. In
fact, per the NAEFS ensemble these 850 mb temperatures will place in
the 99.5th percentile of climatology. 700 mb temperatures are more
impressive as they are placed in the top of all climatology. All
this to say, Saturday will be a hot, humid, and breezy day with
highs warming to the mid 90s and 100s with heat indices into the
100s across the forecast area. Some break in the heat is expected on
Sunday as a cold front will be pushing through the area. Still, high
temperatures will warm to the 90s to low 100s with heat indices up
to 100s. Though the warmest heat indices will reside east of the
James River due to the previously mentioned cold front. Have
extended the Extreme Heat Watch into Sunday for locations along and
east of the James River and left it in place for the entire area for
Friday and Saturday. With the front in the area and the northern
stream upper level jet dropping down to the Northern Plains, showers
and storms may return to the area Sunday evening and night. While
some new record high temperatures could be set during the heat wave,
record warm low temperatures have the highest probability of being
broken.

Although the heat will be done for next week. Confidence is
increasing in rain chances sticking around for a large part of next
week. With the previously mentioned cold front dropping south of the
forecast area, high temperatures will drop to near seasonable levels
in the 70s and 80s. At the same time, the forecast area will reside
in the right entrance region of an the northern stream upper level
jet. While the surface boundary looks to be south of the forecast
area on Monday and Tuesday, the elevated boundary will still remain
over the forecast area. With mean flow parallel to the boundary,
weak shortwave troughs rotating through the upper level flow, and
precipitable water (PWAT) values up to the 90th percentile of
climatology per the NAEFS ensemble, soaking rain will be possible.
Especially as pattern recognition comes into play given how this
pattern looks to play out as a Maddox Frontal Pattern. This is a
known pattern for heavy rainfall and even flooding. The ensembles
support this potential as they show increasing probabilities for
exceeding a half an inch of rain each day Monday through Thursday
next week. Severe weather could accompany the rainfall in this
pattern but at this time, Wednesday and Thursday look to have the
best chances for seeing strong to severe storms as medium range
guidance is in decent agreement in the boundary returning
northwards, bringing greater instability to the area. Starting to
think that this pattern could end up being a longer duration,
lower/weaker rainfall rate event though details can certainly change
as this event draws closer. Please continue to monitor the latest
forecast for the most up to date information.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1214 PM CDT Thu Jun 19 2025

VFR through the period. The main concern will be isolated
strong thunderstorm potential in parts of southwest MN and
northwest IA late evening into the overnight. Also of
concern will be LLWS across southeast SD, northeast NE,
southwest MN and northwest IA late tonight into Friday morning.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Extreme Heat Watch from Friday morning through Sunday evening
     for SDZ039-040-054>056-060>062-065>071.
     Extreme Heat Watch from Friday morning through Saturday
     evening for SDZ038-050-052-053-057>059-063-064.
MN...Extreme Heat Watch from Friday morning through Sunday evening
     for MNZ071-072-080-081-089-090-097-098.
IA...Extreme Heat Watch from Friday morning through Sunday evening
     for IAZ001>003-012>014-020>022-031-032.
NE...Extreme Heat Watch from Friday morning through Sunday evening
     for NEZ013-014.

&&

$$

DISCUSSION...Meyers
AVIATION...08