450
FXUS63 KFSD 161902
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
202 PM CDT Sun Jun 16 2024

.KEY MESSAGES...

- Potential for a higher end severe weather risk tonight into
  Monday across the CWA. Elevated supercells supporting large
  hail to around baseball size will be very possible, with a
  smaller wind risk. Best chances near and north of I-90.

- An increased risk for heavy rain and potentially flash
  flooding will also be present late tonight into Monday.
  Increased confidence that the heaviest rain will be near and
  north of I-90 towards highway 14.

- Low confidence on Monday afternoon and evening but another environment
  may develop which would support elevated supercells and large
  hail.

- Very unsettled pattern through most of next week. Ensemble guidance
  through the week suggests nearly a 50% probability for as
  much as 4" of rain through next weekend. Flooding concerns
  definitely grow during this time given expected pattern.

&&

.DISCUSSION...
Issued at 159 PM CDT Sun Jun 16 2024

By late this afternoon and this evening the low level front
should be near the Missouri River into parts of northwest IA
with the front around 850mb closer to somewhere between the Mo
River and I-90. Model soundings still pretty bullish with
capping of the lower levels, suggesting that any forcing or
parcel ascent below about 850mb will not produce any convection.
The models do have a very weak wave in northeast CO this
morning that moves towards northwest IA by early evening. A few
models try to produce some scattered convection but this seems
very unlikely. Some backing of the low level winds does try to
occur from about 6-8pm, but appears to be more focued southwest
of the area and motion northeast would be slow. The nam seems
too aggressive with moisture around 850mb late afternoon and
early evening which might be why the cap weakens and some
convection develops. Most other models do not have this and
given the latest 850mb analysis the better advection of the
deeper moisture will come later when the main wave ejects onto
the Plains.

Once this wave moves onto the Plains this evening forcing
across the boundary increases significantly and convection
should rapidly develop between about 3z and 6z. The latest HRRR
and Rap showing about 2500- 3000 J/kg CAPE and moderate shear
which will support scattered supercells with the main threat
being large hail, possibly around baseball size. With the deep
stable layer in the low levels tornadoes and wind will be much
lower threats. Model soundings still very consistent in
suggesting that lift from around 800 mb will see the least
amount of convective inhibition which makes that amount of
instability all the more impressive. The models are in good
agreement on the 800 mb front being roughly from Gregory SD to
Flandreau SD to Marshall MN from about 3-6z. The location of
this boundary will be something to watch through the evening in
case it slides a little farther south this afternoon. Once
development takes place supercell motion would likely be east
northeast with some potential to build southward into the lower
level forcing as deeper moisture and increased instability work
into the area.

The other concern with this set up will be heavy rain. The upper
level flow is still expected to be normal to the low and mid level
boundary and with the upper level wave slow to move northeast
backing of the mid level winds remains in place through at least mid
day Monday which will likely support continuous development through
Monday into Monday night. Latest models indicating a very good
chance for 2-4 inches of rain north of I-90 from around De Smet then
into southwest MN.

Really tough to say for sure what will happen from later Monday
afternoon into Monday night as tonight and Monday mornings activity
will dictate the environment a bit, but given the strength of the
wave will not be relying on only instability to get storms going
again. By Monday afternoon and Monday night an environment capable
of strong elevated supercells may exist once again and another round
of severe weather and heavy rain will exist. Once again the
environment would be most supportive north of I-90 and possibly west
of I-29. Some upper level ridging should keep northwest IA,
northeast NE and far southeast SD with very small chances for
thunderstorms Monday mid afternoon into Monday night.

Upper level troughing to the northwest begins to shift east Monday
night into Tuesday and will likely bring renewed chances for showers
and thunderstorms into Tuesday night with severe weather again
possible. The better chances will be east of the James and likely
east of I-29.

This system passes and cooler and less unstable air settles in, but
for now that does not look like the end of rain and thunderstorms.
The right entrance region of the upper level jet lifts northeast and
once again enhances low to mid level flow, bringing additional lift
and moisture into the area and thus more rain and thunderstorms. A
lot between now and then but right now this not does not look like
as big of a severe threat, but with the rain possible near and east
of I-29 again flooding concerns will begin to grow.

Thursday into Sunday will see continued chances for showers and
thunderstorms with mostly westerly flow aloft which brings in
occasional weak waves. Temperatures should be seasonally warm most
days.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1155 AM CDT Sun Jun 16 2024

Scattered MVFR ceilings mainly west of I-29 today, some of this
will lift to VFR through the afternoon. The main concern will
be thunderstorm potential. At this time it appears that most of
this activity will hold off until roughly 3z or later. Some very
isolated showers and thunderstorm activity will be possible
from about 0-3z but much lower confidence in this development.
Between 3-6z rapid development is expected in central SD
eastward to near and between I-90 and highway 14. Severe
thunderstorms are expected with this activity as well as heavy
rainfall. Occasional development is expected through the night
into Monday morning. Areas south of I-90 will see much more
isolated activity. MVFR and IFR ceilings will also become more
likely late tonight into Monday with slightly lower confidence
in these lower ceilings in northwest IA.

&&

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

&&

$$

DISCUSSION...08
AVIATION...08