889
FXUS63 KFSD 210928
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
Issued by National Weather Service Lincoln IL
428 AM CDT Fri Jun 21 2024

.KEY MESSAGES...

- Another round of heavy rain is likely tonight with the
  development of another MCS. Probabilities of over 2 inches of
  rain are around 60-80%, focused generally south of a Sioux
  Falls to Jackson MN line and north of US-18.

- The Flood Watch has been expanded southward a bit in Iowa to
  include Plymouth, Cherokee and Buena Vista Counties.

- Extensive river flooding will develop over the next day or
  two, with best chances of reaching major flood stage on parts
  of the James, Vermillion and Big Sioux Rivers.

&&

.DISCUSSION...
Issued at 425 AM CDT Fri Jun 21 2024

Through Saturday:

Expansive MCS that produced widespread 3 to 6 inch rains across
the heart of the forecast area has shifted eastward early this
morning, with the heaviest rain in northwest Iowa as of 4 am.
However, numerous flash flood warnings continue along the I-90
corridor and in the row of counties south of there.

Latest surface map shows the stationary front draped across
northern Nebraska to about the US-18 corridor in northwest Iowa.
High-res models continue to show convection redeveloping near it
through the afternoon, then another MCS firing later this
afternoon and moving through the forecast area this evening.
Precipitable water values remain highly anomalous into tonight
for the area (around 1.9 inches, near record territory for this
time of year per Aberdeen/Huron sounding climatology). As one
might imagine, flash flood guidance is extremely low in the
areas that have been pounded overnight, but is around 1.5 inches
a little further south toward Sioux City. The Flood Watch has
been expanded a bit further to include Plymouth, Cherokee and
Buena Vista Counties in Iowa. Probabilities of seeing another 2
inches of rain are high (60-80%), though the exact alignment is
a bit uncertain given the ongoing activity. NBM guidance would
favor more of an area near and north of I-90, while the HREF
begins to shift it more near and south of the MN/IA border. Much
of the rain should be out of the forecast area by midday
Saturday, though lingering into the afternoon east of I-29.


Sunday through Thursday:

A couple welcome days to dry out are expected to start the new
week, as upper level ridging slides across the Plains. Once we
get to Monday night and Tuesday, global models are in agreement
with a strong upper low moving across the Lake Winnipeg region,
drawing more of a northwest flow into the Dakotas. The
associated surface cold front moves through Monday night and
Tuesday morning, though the general trend suggests the heaviest
rain amounts more to the north and northeast of the forecast
area. Temperatures are expected to peak on Monday in the lower
90s, but drop off by mid week to the upper 70s near the Buffalo
Ridge and mid 80s along the Missouri River.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1117 PM CDT Thu Jun 20 2024

Showers and thunderstorms - some with heavy rain - will expand
eastward overnight, with the focus from south central SD and along
and north of the Interstate 90 corridor. The activity may
diminish on Friday morning, before showers and thunderstorms
develop once again along and north of Interstate 90 in the
afternoon and evening. Some of these storms could be severe,
with heavy rain likely. Visibility and ceilings will be in the
MVFR/IFR range with any shower and thunderstorm activity. Other
than in thunderstorms, east to southeast winds will be
relatively light through the TAF period.

&&

.HYDROLOGY...
Issued at 425 AM CDT Fri Jun 21 2024

MRMS rainfall estimates since about mid afternoon Thursday show
a substantial area of 3 to 4 inches of rain across the heart of
the forecast area, with upwards of 6 inches across Turner and
Lincoln Counties in SD and and Lyon County IA. With this amount
of water and another slug of hefty rain amounts expected
tonight, moderate to major flooding is likely to develop over
the next couple days along parts of the James, Vermillion, and
Big Sioux Rivers.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Flood Watch through Saturday morning for SDZ038>040-050-
     052>071.
MN...Flood Watch through Saturday morning for MNZ071-072-080-081-
     089-090-097-098.
IA...Flood Watch through Saturday morning for IAZ001>003-012>014-
     020>022.
NE...None.


&&

$$

DISCUSSION...Geelhart
AVIATION...JM
HYDROLOGY...Geelhart