835
FXUS63 KFSD 152003
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
303 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Very conditional risk for a few stronger storms near and east of I-
29 late this afternoon and evening. The greatest risk will be from
hail but an isolated tornado cannot be ruled out.

- Heat advisory criteria will be approached over Nebraska and Iowa
Sunday afternoon and possibly Monday afternoon.

- Potential for a higher end severe weather risk Sunday night into
Monday across the CWA. Very large hail will be the primary risk, but
some wind risk could develop. Confidence remains low to moderate on
location and timing.

- Additional concerns for heavy rain and flash flooding late Sunday
night into Monday. Though some uncertainty exists on where this rain
axis may develop.

- Very unsettled pattern through most of next week. Ensemble
guidance through the week suggests a 40-60% probability for as much
as 2-4" of rain by next weekend.

&&

.DISCUSSION...
Issued at 301 PM CDT Sat Jun 15 2024

Instability slow to recover after a morning MCS in eastern NE has
carved out a large relatively stable air mass. The outflow can be
seen on satellite extending from eastern KS into central NE early
this afternoon. With the wave in place across central NE into
eastern SD a combination of diurnal heating and increased southerly
flow should gradually work through this stable air mass. A decent
pool of instability at 1500-2000 J/kg CAPE exists across south
central NE which should spread northeast. The big question mark is
just when storms may fire. With the delayed response from the
morning MCS the deeper instability may not approach far northeast NE
and northwest IA until closer to 0z, bringing the best chance for
isolated severe storms into northwest IA from about 7 pm to 11 pm.
While the overall shear profile is not very impressive the lowest km
or so does have some decent speed and directional shear along with a
fairly low LFC/LCL which means an isolated tornado cannot be ruled
out. If development is much later than 0z isolated hailers will be
the main threat.

Once this wave passes this evening, weak mid and upper level ridging
will build into the area as a strong low level cap develops. This
cap will server a couple of purposes. The first will be to suppress
any convective potential on Sunday afternoon and possibly into the
early evening, even with an incoming weak boundary. The other
purpose this boundary will serve is to limit mixing and allow
moisture to pool near and ahead of this incoming front, resulting in
surface dew points in the upper 60s to lower 70s. Combined with
highs of 90 to 95, heat indices in mostly northwest IA could climb
to around 100 in the afternoon.

This brings us to Sunday night into Monday. The big battle will be
between capping and forcing/moisture. A significant cap will
continue into Sunday night, and current trends suggest that just
about any parcel that tries to lift below about 850-800mb will not
make it. This suggests we may need to wait for the main wave to
eject northeast late Sunday night which would put the main threat
for any severe weather and heavy rain from about midnight to noon
Sunday night into Monday. Just how much instability will exist if
lifting above 800 mb will be a big question. Overall there will be a
late evening threat for some isolated elevated supercells with
damaging hail the biggest threat, but the main threat will be later
in the night with a likely lesser severe threat but a higher heavy
rain threat. This potential continues to remain highest near and
especially north of I-90.

The models become less agreeable Tuesday into Wednesday with the
strength of the wave to the northwest and the resultant position of
the surface front. For now not enough confidence to worry about a
whole lot during this time, but there will be a continue threat for
showers and thunderstorms.

Once the convective potential lifts north on Monday morning the
precipitation chances should wane, but another system is expected to
move into the area on Monday night into Tuesday which will bring a
renewed threat into the area. The better chances appear to be near
and west of I-29.

The pattern remains active Thursday into Saturday with seasonally
warm and humid conditions. The flow aloft is expected to become a
bit more westerly but still indications that multiple weak waves
will traverse this flow and bring continued chances for showers and
thunderstorms.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1204 PM CDT Sat Jun 15 2024

Some residual MVFR ceilings are expected into the afternoon as
light rain wraps northeast. The better chances for MVFR
conditions will be north of I-90. Attention then turns to the
potential for the development of stronger showers and
thunderstorms. Some spotty showers and thunderstorms will be
possible near and east of I-29 this afternoon, with lightning
and brief heavy rain the main threats. Very late this afternoon
into the evening over northeast NE, northwest IA and parts of
southwest MN some stronger to possibly severe storms will
develop. After about 5z this activity should be east of the area
with VFR conditions to finish out the TAF period.

&&

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

&&

$$

DISCUSSION...08
AVIATION...08