617
FXUS63 KFSD 290804
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
304 AM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Rivers across the area have crested or are presently at
  crest. Should see levels continue to slowly trend downward
  this weekend, with largely dry conditions expected to prevail.

- Below normal temperatures continue today into Monday, with the
  coolest temperatures Saturday through Monday.

- Stronger westerly flow aloft develops Monday through the end of
  the week which should bring a bit busier pattern next week.

- Monday and especially Monday night will be the next better
  chance for severe weather and heavy rain. Higher confidence
  in showers and storms (60-80%) with decent chances for more
  than an inch of rain in northwest IA (20-40%). Definitely a
  time frame to keep an eye on.

&&

.DISCUSSION...
Issued at 302 AM CDT Sat Jun 29 2024

Drier and cooler air surges into the region this morning bringing
marginally breezy conditions and temperatures well below normal,
about 10-15 degrees below normal. Highs will generally be in the
upper 60s to lower 70s. While any meaningful rainfall is not
expected, some very weak instability at the top of the mixed
layer could produce an isolated sprinkle or very light shower
late this morning into the afternoon. With high pressure
settling in at the surface this afternoon and evening, winds
will drop off quickly and bring a pleasant, but cool evening.
This will lead to some chilly temperatures on Sunday morning.
Lows should be in the mid 40s to lower 50s.

High pressure slowly shifts east of the area on Sunday, allowing for
a bit warmer temperatures to return. This should lead to highs more
in the lower to mid 70s as well as a breezy southerly wind west of I-
29. Moisture below about 700 mb is pretty scarce so at least on
Sunday and Sunday night will need to look at the EML and with fairly
steep lapse rates some ACCAS showers and thunderstorms will be
possible. The challenge appears to be whether or not we can get some
moisture into the 800-700 mb layer to help bust through the mid
level capping. With an increasing upper level jet and a weak mid
level wave some mid level moisture should aid in producing some
convective activity. More than likely this activity will be sub-
severe as instability and shear are not quite there. The better
chance for ACCAS showers and thunderstorms will be Sunday night as
the moisture begins to increase a bit.

Monday will be the next chance for severe storms, with the better
chance coming Monday night. The challenge may be a decent mid level
wave moving through the area during the day on Monday which will
likely suppress any deeper instability into Nebraska. As is the case
in most events the Nam appears to be overdoing the instability, but
both the Nam and GFS agree that any activity should be elevated,
likely about 850mb. It looks like the 925 mb to surface instability
will remain to the south. So, with decent shear and instability an
isolated stronger updraft or elevated supercell could produce golf
ball sized hail and wind gusts to 60 mph. Right now confidence is
fairly low on this activity. One thing to watch out for will be
heavy rain, especially across parts of northwest IA where both the
GEFS and EC ensemble point towards the higher chances. This matches
up to closely to some fairly strong forcing within the LLJ, so this
will need to be monitored closely because of the recent flooding.

Lingering showers and thunderstorms will be possible on Tuesday but
for now the severe threat looks low. Tuesday night into Wednesday
looks dry and seasonally warm with lows 55 to 65 and highs in the
upper 70s to mid 80s.

Thursday into Friday has a fairly well agreed upon system that moves
through and will likely keep temperatures below normal. With
Thursday being the 4th of July will need to keep an eye on trends as
any shower and Thunderstorm activity may alter some plans.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1055 PM CDT Fri Jun 28 2024

VFR conditions with relatively light northwest to north winds are
expected through the overnight hours. After daybreak, most likely
after 12Z-13Z, a secondary cool front drops south, followed by
areas of stratus which could bring a period of MVFR ceilings to
areas near/north of I-90 Saturday morning. This most likely to
impact KHON, but could also brush KFSD before the stratus lifts
above 3kft AGL.

Gusty north-northwest winds will also accompany this stratus,
with frequent gusts 20-25kt expected through sunset Saturday
evening.

&&

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

&&

$$

DISCUSSION...08
AVIATION...JH