145
FXUS63 KFSD 191938
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
238 PM CDT Wed Jun 19 2024

.KEY MESSAGES...

- The main concern through Saturday morning will be heavy rain with
  periods of showers and thunderstorms each day.

- Showers and isolated thunderstorms will build into the area
  late tonight through Thursday. Severe weather threat is very
  low, but have high confidence in widespread rain. Better
  chances for a half an inch or more of rainfall tonight into
  Thursday morning will be west of I-29.

- Moisture deepens and instability increase late Thursday
  afternoon into Thursday night which will being a higher risk
  of heavy rain and isolated severe storms. Looking like a
  50-70% chance for an inch or more of rainfall in southeast SD
  and southwest MN.

- Risks for thunderstorms continue into Friday, with potential
  for strong to severe storms Friday afternoon and night and
  periodic chances for heavy rainfall. All modes of severe
  weather will be possible but with all of the expected Activity
  tonight through Friday morning confidence is low on this
  occurring..

- Cooler temperatures and likely dry conditions Saturday night
  into early next week, though rain chances return Monday night
  through Wednesday.&&

.DISCUSSION...
Issued at 237 PM CDT Wed Jun 19 2024

Moisture has been pushed south of the area and will take a bit of
time to return. The right entrance of the upper level jet and
attendant mid level wave will move onto the Western High Plains
tonight into Thursday morning. This will help moisture to return but
initially tonight this moisture will mainly be in the mid levels.
Because of this instability will be limited with CAPE values
generally less than 500 J/kg. So overnight the main threats should
be lightning and locally heavy rainfall. Any higher amounts should
be limited to areas mainly west of I-29. The GEFS is more limited in
producing a half an inch more more of rainfall during this time
while the EC ensemble is suggesting a very good (roughly 60%) chance
for a half an inch or more. With the limited elevated moisture and
weak instability think that any higher amounts of rainfall before
12z Thursday morning will limited in area.

As this wave slowly drifts northeast through the morning on Thursday
another wave will move onto the Western High Plains which will
continue to the mid level warm advection. This should bring an
increase in low and mid level moisture into Thursday night, but the
latest model soundings still suggest marginal instability with CAPE
values around 1000 J/kg. Deep layer shear values are not too bad and
given some decent instability could see some isolated severe storms
and once again the threat for heavy rain given the freezing level
around 13 kft and upper level winds close to normal of the low level
front. Currently the better chance will be central SD into areas
north of I-90.  Overall the threat for heavy much higher on Thursday
night into Friday morning with a much stronger LLJ, a bit more
instability, continued deep warm layer and a slightly stronger wave.
Latest HREF showing a fairly widespread 2-4" of rain near and north
of I-90 into central SD Thursday night into Friday morning with the
axis of higher chances for 2+" of rain on the GEFS along the same
corridor as well as the EC Ensemble which is showing a 40-50%
chance for 2+".

Friday night into Saturday poses the next better severe weather
threat with a surface warm front expected to be in place near and
north of I-90. With all of the potential activity between now and
then confidence is pretty low on coverage and severity, but with
moderate instability and shear and the surface front nearby, all
modes of severe weather will be possible. Latest ensemble
projections place this front near highway 14 late Friday afternoon
into the evening. An of course if the majority of the activity
develops near and north of I-90 and the potential for heavy rain
Thursday night into Friday happens we may see some flooding concerns.

Once this system passes Saturday night into Monday looks mainly dry
as upper level ridging builds in. The should allow for seasonally
warm temperatures with lows in the 60s and highs in the 80s.

Scattered showers and thunderstorms will become possible again
Tuesday into Wednesday next week as westerly flow increase and
swings through a few weak waves. This should increase low and mid
level southerly flow and help return moisture and instability to the
area.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1213 PM CDT Wed Jun 19 2024

Very patchy MVFR ceilings still lingering into the early
afternoon, but confidence is low. Scattered showers and isolated
thunderstorms are expected to expand in coverage from 0-6z this
evening, especially west of I-29. These showers and storms will
then expand in coverage eastward overnight into Thursday
morning. The main threats from any storms will be lightning and
locally heavy rainfall. Late tonight into Thursday morning
ceilings will likely also lower MVFR over much of the area.

&&

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

&&

$$

DISCUSSION...08
AVIATION...08