369
FXUS63 KFSD 160811
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
311 AM CDT Sun Jun 16 2024

.KEY MESSAGES...

- Potential for a higher end severe weather risk Sunday night
  into Monday across the CWA. Very large hail (>2") will be the
  primary risk, but some wind risk could develop.

- An increased risk for heavy rain and potentially flash
  flooding will also be present late Sunday night into Monday.
  Though some uncertainty exists on where this rain axis may
  develop.

- More humid conditions may not be as extensive on Sunday, and
  lingering clouds will may keep the warmest conditions near the
  Missouri River and Highway 20 corridor Monday.

- 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 306 AM CDT Sun Jun 16 2024

THIS MORNING:  Convection continue to move away from the CWA this
morning, leaving southerly winds and warm overnight temperatures in
it`s wake. A secondary mid-lvl shortwave is moving through the James
River valley early this morning, though any convection with it has
since dissipated.   Further west, we`re beginning to see a cool
front surge eastward, likely reaching the western CWA by daybreak.

TODAY: The aforementioned front will continue to surge southeast
through the daytime hours today, likely falling along a line from
Grand Island to Storm Lake and Albert Lea by late this afternoon.
Guidance has trended cooler with temperatures this afternoon, with
highs likely to stay in the lower to middle 80s in most areas, with
only a slight chance for reaching 90 closer to the front.  Surface
moisture will also push further south, making 100 degree apparent
temperatures less likely in northwest Iowa. Latest guidance
continues to support a fairly significant CAP along the front
later this afternoon, making surface based convection a bit less
to form late this afternoon. If for some reason a storm could
get going along the front, given the reservoir of MLCAPE, large
hail and some 60 mph winds would be likely. One sign of
incoming moisture we may see later this afternoon will be a few
very high based showers moving through central and northeastern
SD, indicative of the increasing isentropic lift and moisture
return within the 315- 320K isentropic sfcs. It`s possible the
southern zone of this lift, may mark the northern zone of where
overnight rain could fall.

TONIGHT:  Multiple hazards are anticipated through the overnight
hours, with the biggest question being how soon will risks develop
and where the greatest risks will be focused.  By 00Z moisture is
expected to surge north on the wings on a 40 to 50 knot 850 mb LLJ,
with sharpening mid-lvl lapse rates allowing upwards of 2000-3000
J/KG MUCAPE to reach the I-90 corridor by 03s.  While a few elevated
hailers could be possible south of I-90 by mid-evening, large scale
deep ascent begins to arrive after 10pm as a shortwave enters the
Plains from the southwest.  Increasing mid-upper diffluence should
lead to rapid upscale growth in convection as the midnight hour
arrives. Uncertainty still remains on where this corridor of lift
will develop. The HRRR/RAP remain far northern outliers north of
Highway 14, while the GFS and many of it`s ensemble members focus
along or south of I-90.   The EC/CMC and several high resolution
CAMs suggest the prime corridor would be somewhere either side
of a Chamberlain to Madison to Marshall line. With lift focused
along the 850 mb layer, effective shear may push 50 knots at
times, and would support elevated supercells moving from
southwest to northeast along the elevated front. Hail is likely
to be the predominate threat with analog soundings suggesting
potential for 2-3" diameter hail if the significant mid-lvl
lapse rates can develop.

The other main concern will be heavy rain. As we`ve mentioned
before, many of the ingredients for high rainfall rates are
expected tonight. PWATs approaching 200% of normal, deep warm
cloud depths, semi-parallel flow along the elevated boundary
(likely leading to training cells), and persistent mass
convergence within the effective lifting layer. NBM QPF remains
somewhat spread out given variability in ensemble data tonight,
but feel there will be a corridor of 2-4" rainfall within the
CWA wherever the convergence axis develops. Have tried to blend
in a bit of HREF PMM guidance within the current NBM QPF from
06-12Z. A flood/flash flood watch could be needed, but given
uncertainty in location, will leave to next forecast shift to
watch for some signs of where this development could take place.


MONDAY-MONDAY NIGHT: Convection will not just shut off by 12Z
Monday, as the deep southwesterly flow continues through the
morning. It may not be until the mid-lvl shortwave drive east late
in the morning for the rain to gradually end.  Eventually, falling
heights over the western High Plains will try to force the surface
front northward, with a secondary cold front developing over central
SD. An extremely unstable environment develops within the warm
sector by Monday afternoon, however most of it may be capped.  One
focus for afternoon redevelopment may be along the front west
of the James River, but lower risks for isolated elevated
convection could be possible further east in the evening. With
the surface warm front/stationary front focusing the best mass
convergence north of the CWA, the focus for heavy rain may also
shift just northeast of the area as well. It`s possible most of
Monday night could stay dry.

TUESDAY:  Uncertainty does begin to grow by Tuesday, though most
models push a cold front southeast early in the day. Convection may
develop along this front early Tuesday afternoon, likely along and
east of a line from Brookings to Yankton. Given the residual
instability in the area, severe weather risks will again be
possible, though lower effective shear may support more multi-
cellular bowing segments into the early evening. Temperature
Tuesday afternoon ahead of the front may push the upper 80s,
with heat index values rising into the 90s.

WEDNESDAY-SATURDAY:  A busy week in the mid-upr Missouri River
valley is expected into next weekend as the synoptic pattern remains
primed for repeated convection risks.  With the surface front and
low-lvl baroclinic zone nearby, any perturbation moving through
the quasi-zonal to southwest flow should initiate convection.
With PWAT values holding near 150-175% of normal, heavy rain
will be a risk in any convection. Ensemble probabilities (even
given individual member variance) remain nearly 50% over a large
area for 4"+ of rainfall. It`s highly likely that localized
areas could see more.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1055 PM CDT Sat Jun 15 2024

Mainly VFR conditions with southerly winds will prevail
overnight. Showers and isolated storms continue to exit eastward
out of northwest IA. Further west, showers and isolated storms
continue to spread east from central SD into eastern SD
overnight. Severe weather is unlikely with this activity, but
there may be occasional MVFR stratus sliding in underneath the
cirrus near and east of the I-29 corridor overnight.

VFR conditions will prevail across the region through the day
and early evening Sunday. A passing cold front will turn winds
southwesterly and eventually northwesterly at KHON and KFSD on
Sunday, becoming stationary between KFSD and KSUX by the end of
the day. Another round of showers and strong to severe storms
is expected to spread into the region late Sunday night.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...BP