769
FXUS63 KFSD 161116
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
616 AM CDT Mon Sep 16 2024

.KEY MESSAGES...

- Temperatures remain above normal through mid to late week.
  Nighttime lows show greater departures above normal (10-15F)
  than daytime highs (5-10F) due to anomalously high low level
  moisture/dew points.

- Low (generally < 20%) rain chances today through Tuesday
  afternoon. Confidence in timing and placement is low, but
  expect amounts to remain light, with less than a quarter inch
  through this period at any location.

- Greater chance for rain (40-70+%) Tuesday night through
  Wednesday, mainly focused Tuesday night west of I-29. Moderate
  (~ 40%) probability of rainfall exceeding 0.25", but low (<
  25%) probability of exceeding 0.50".

- Moderate chances (40-60%) for showers/storms late week into
  the weekend, with highest chances currently focused Thursday
  night and Friday night through early Sunday. Exact timing and
  location remain uncertain.

&&

.UPDATE...
Issued at 604 AM CDT Mon Sep 16 2024

Storms this morning have been more robust in development than
was previously expected west of I-29, likely aided by the
combination of the LLJ and a very subtle vorticity lobe moving
northeast out of NE. Although severe weather is not expected,
some storms may produce wind gusts to 50 mph and dime size hail
in addition to frequent lightning and locally heavy rain. Hi-res
guidance continues to handle this activity poorly, but based on
how these LLJ enhanced events typically trend, expect storms to
taper off late this morning.

&&

.DISCUSSION...
Issued at 348 AM CDT Mon Sep 16 2024

TODAY AND TONIGHT: Early this morning, watching a wave track through
the western and central portions of the Dakotas, and the main upper
low across central CA. This leading wave continues to lift off to
the north-northeast through the morning and early afternoon, which
may bring some isolated showers and storms to areas west of the
James River this morning, and toward the southern MO River Valley
into the afternoon. Models show some of the forcing splitting off of
the wave, and hence the lower end pops through the afternoon into
the southern MO River Valley. Given how the hi-res guidance has been
handling convection the last few days, did not focus on any one
model, but did try to incorporate some of the broad trends for
timing and location. Next wave ejects out through the overnight
hours, leading to some additional low (20%) pops west of I-29
tonight. Precipitation may struggle at times to reach the surface
with dry air below the cloud layer. Severe weather is not expected,
but some stronger gusts are possible. Storms may be elevated, so
can`t entirely rule out some small hail.

Breezy southeast winds are expected today and tonight - especially
west of I-29. Surface pressure gradient (SPG) is compressed, and we
may mix down some gusts to 35 mph west of the James River. Should
stay below Wind Advisory criteria though. Warmer than average
temperatures remain in place, with highs in the mid and upper 80s.
Lows in the mid and upper 60s with southeast flow aiding in the mild
overnights.

TUESDAY AND TUESDAY NIGHT: Any isolated to scattered showers and
storms on-going Tuesday morning continue through the afternoon as
the strongest wave and WAA lift through the area. Not expecting any
severe weather, but again, a stronger storm could produce some
gustier winds and small hail. Today through Tuesday afternoon, light
rainfall is expected with totals less than a quarter of an inch.

More widespread breezy conditions expected Tuesday and into Tuesday
night as the SPG tightens in response to developing low pressure on
the lee side of the Rockies. As of now, low probability (less than
20%) of sustained or gusts reaching Wind Advisory criteria, but will
keep an eye on potential if mixing is more robust than expected.
Highs on Tuesday again in the mid to upper 80s, with lower 90s west
of the MO River. Lows in the 60s.

WEDNESDAY THROUGH MONDAY: Continued chances for rain mid week
through the first half of the weekend thanks to the unsettled
pattern. Mid week, low pressure swings northeast out of the Rockies.
Although the center of the low is progged to move into ND, we`ll see
a plethora of shortwaves track across the area into the end of the
week. As this low lifts north, the next one is already deepening
over the southwestern US. This second wave and upper jet support
move east through the first part of the weekend and into the central
Plains Sunday. There is more agreement in the 16.00z runs than the
15.12z runs in the track of the second low, but timing remains
uncertain. Currently, best chances for rain and isolated storms are
expected Thursday night and again Friday night through Saturday
night. However, expect further refinements as agreement in the
details increases. Above average temperatures continue into at least
Friday. Near to possibly below normal temperatures for the weekend,
depending on the timing and exact track of the second low pressure
system. Given uncertainty, rainfall amounts are uncertain through
this period.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 604 AM CDT Mon Sep 16 2024

Outside of convection, expect VFR conditions to prevail. As
mentioned in the Update section of this discussion, activity has
been more robust than previously expected west of I-29.
Included a VCTS mention at KHON, but will watch trends in case
storms hold together and move into the airspace. Additional
showers and storms are possible this afternoon in the southern
MO Valley, and along/west of I-29 tonight; however, given low
confidence in coverage and occurrence, have omitted from KFSD
and KSUX with this forecast.

Southeasterly winds increase today, with gusts around 25 to 30
knots west of I-29. Gusts around 20 to 25 knots expected
elsewhere. Gusts are expected to continue tonight, and thus have
not included any mention of LLWS. If gusts drop off overnight,
LLWS is possible across the area, with the greatest threat west
of I-29.


&&

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

&&

$$

UPDATE...SG
DISCUSSION...SG
AVIATION...SG