280
FXUS63 KFSD 151708
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1208 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Rain will continue to move northeast through the morning
  hours of Saturday. Persistent showers into the afternoon may
  limit temperatures.

- Very conditional risk for a few stronger storms over
  Northwest Iowa and southern Minnesota later this afternoon and
  evening. The greatest risk will be from hail.

- Heat advisory criteria may be approached over Nebraska and
  Iowa Sunday and 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.

- 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 nearly a 50% probability
  for as much as 4" of rain by next weekend.

&&

.DISCUSSION...
Issued at 304 AM CDT Sat Jun 15 2024

THIS MORNING:   Large MCS continues to work eastward across eastern
Nebraska this morning.  Further north, rainfall has generally been
very light due to the presence of high bases and sub-cloud dry air.
CAMs all indicate rainfall will increase throughout the Tri-State
area after 3am, with the associated lobe of vorticity moving into
southwest Minnesota by mid-morning.  Rainfall rates have been less
than expected, and overall QPF has lowered into the morning.

TODAY-TONIGHT: Most CAMS suggest this initial lobe of vorticity
moves north east of the CWA by late morning.  However have some
concerns that the persistent southeast low-lvl warm advection
persisting into the afternoon ahead of a slightly positively
tilted mid-lvl trough moving into eastern SD/NE may keep
scattered showers going well into the afternoon. Regardless the
increase of cloud cover should cause temperatures to stay much
cooler in the 70s, with some potential for a late day climb
towards 80. Uncertainty remains fairly high for severe weather
potential later this afternoon/evening. In the wake of the
morning MCS, we may see some sort of differential heating
boundary develop south of the CWA by the afternoon which will
try to lift northward into early evening. CAMS are all over the
place as to how far this can travel this afternoon, but there
remains some potential for upwards of 2000 J/KG MLCAPE across
portions of southeast South Dakota, northeastern Nebraska, and
northwest Iowa by 21Z. With lift arriving from secondary trough
sliding eastward, convection may initiate quickly by 21Z and
then track into northwest Iowa. While deep layer shear is
marginal, given steepening mid-lvl lapse rates, large hail up to
1.5" seems to be the most likely threat, with a secondary wind
threat. Depending on how the surface evolves, cannot discount
the tornado threat as long as storms can stay rooted into the
boundary layer. 0-1km helicity values push 100-150 m2/s2, 0-3KM
CAPE is pushing 250 J/KG, and LCLs are quite low at 1800 ft AGL
across most of northwest Iowa. The positive is that this threat
will not go long into the overnight with most of the risk east
of the CWA by 9pm. In the wake of the rain light winds may allow
for some fog development. Further west, a few models hint at
decaying convection reaching central South Dakota after
midnight.

SUNDAY: A surface front is expected to sink southward into northeast
Nebraska and stretch into southern Minnesota by mid-day Sunday. 70
degree dewpoints will likely pool along and south of this front by
Sunday afternoon and with temperature surging into the 90s over
eastern Nebraska and portions of northwest Iowa, heat index values
may push 100 degrees.  Further northwest, temperatures will be
cooler in the lower 80s.

SUNDAY NIGHT:  Increasing concerns for both severe weather and heavy
rain risks Sunday night.   Aforementioned frontal boundary will
serve as a focal point (especially north of the boundary) for
convection to develop after dark.  An intensifying LLJ, sharpening
frontogenesis, and broad dPVA within strong southwesterly mid-lvl
flow will provide all the ingredients needed for convection to
develop.  Soundings suggest the greatest focal point for lift will
be within the 850mb zone, which would provide upwards of 2500-3000
J/KG MUCAPE.  Deep layer shear 40-50 knots, and mid-lvl lapse rates
within the prime hail growth zone approaching 7-7.5 C/KM would
support the potential for very large hail AOA 2".  If storms stay
rooted closer to the surface front, then a damaging wind risk could
also develop.   The strong moisture convergence within the 925:850
mb layer also push PWAT values over 175% of normal by late Sunday
night. Given steering flow nearly parallel to the surface
boundary, very high warm cloud layers surpassing 14K ft AGL, and
large volume of MUCAPE, would anticipate some very high
rainfall rates. The biggest uncertainty is where the surface
front will become established and where the zone of greatest
lift will form. All-in-all, agree with WPC slight risk for
excessive rainfall, with some CAMs suggesting 2-3" of rain.

MONDAY-MONDAY NIGHT:  Convection north of the boundary may continue
well into Monday, which will keep a high temperature gradient across
the front into the early afternoon.  Eventually there are some
thoughts that as heights deepen over the Central Rockies, we`ll
begin to shift the frontal boundary northward and westward late in
the day, placing the greatest risk for afternoon and evening
redevelopment west of the James River and north of Highway 14.
Temperatures will have a late day surge south and east of the
boundary, with most areas reaching into the upper 80s to lower 90s,
though where the front ends up is still highly in doubt.   PoPs
remain fairly high into the overnight hours of Monday, through
this is likely due to the high degree of uncertainty in ensemble
guidance and impacts on the NBM. In reality the chance for rain
and associated QPF may be much lower. Another corridor of very
heavy rain is likely Monday night wherever the sfc warm front
become established. This should be north of the CWA into central
Minnesota, but we`ll have to watch closely.

TUESDAY-SATURDAY:  It`s difficult to go into too much detail for the
rest of next week as there are so many mesoscale details that will
have to play out first.  The overall pattern continues to be one
that is going to be very active into next weekend. Eventually the
frontal boundary moves back south on Tuesday bringing more rain to
the region.  However the mid-lvl flow flattens through the Plains
for the rest of the week, keeping the surface front and low-lvl
baroclinic zone very near the CWA into next weekend. This may end up
being a classic setup for repeated rounds of convection along the
boundary, and given the high PWAT values in the region,
significant rainfall potential exists. In fact, the probability
of >4" of rain by next weekend is around 50% in the ECE, 40% in
the GEFS, and 70% in the CMC. Even more concerning are the
spotty 10% probabilities for as much as 8" of rain in the Tri-
State area.

&&

.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...Dux
AVIATION...08