541
FXUS63 KFSD 061953
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
253 PM CDT Mon May 6 2024

.KEY MESSAGES...

- Wind Advisory in effect for most of the forecast area through
  early this evening. Gusts to up to 40 to 50 mph expected.

- Thunderstorms will increase in coverage late this afternoon
  and evening, forming a line as it moves toward the I-29
  corridor by early to mid evening. Some of these storms may be
  strong to severe with damaging winds up to 70 mph the primary
  risk.

- Periodic rain chances continue for much of the upcoming week
  into next weekend with the focus on Wednesday. Highs in the
  60s to 70s are expected.

&&

.DISCUSSION...
Issued at 250 PM CDT Mon May 6 2024

Rest of Afternoon and Evening: At a large scale, pronounced
mid/upper low is evident on WV imagery across the northern Rockies
with surface low deepening across western SD. A warm front is
lifting through central NE with a narrow warm sector before a
quickly approaching dryline/cold front is crashing eastward. These
features will all lift east or northeast into the evening and
overnight hours and provide for thunderstorm chances.

Severe Storms: Forecast soundings show a ribbon of modest elevated
instability lifting from roughly 850:800 mb around 1000 J/kg with
higher values as you go south. Surface parcels would obtain closer
to 50o J/kg if they can overcome a modest inversion, although
current thinking is this may be tough given persistent cloud cover
thus far. A robust and dynamic wind field through the entire
atmospheric column is helping to drive deep layer shear of 40-50 kts
however effective shear for elevated parcels looses a good chunk of
the lower directional and speed shear. If a surface parcel can be
realized, nearly 30 kts of 0-1 km shear exists with a well curved
elongated low level hodograph.

With the above stated, well forced dynamics should result in
increasing coverage of storms through the second half of the
afternoon with likely a rapid transition to linear mode. Damaging
wind gusts up to 60-70 mph seems the most likely threat with a 50 to
55 kt LLJ at 850 mb. Even less organized convection may be able to
tap into this higher momentum air, especially while the boundary
layer remains mixed during the daylight hours. Hail would be a
secondary risk although again, elevated parcels lack a better
effective shear profile. Any tornado threat would be conditional on
realizing surface parcels and at this time seems low but should be
monitored given the low level wind field. Any more organized bowing
segment that can orient from northwest to southeast would also need
to be monitored with 0-3 km shear vectors out of the SW AOA 30 kts

Heavy Rain: PWATs around 1.25, and near the top of climatology,
should provide for a period of heavy rain with the passage of the
line of thunderstorms but with a warm cloud layer generally less
than 10 kft and the progressive nature of any thunderstorms, any
flash flooding threat should remain isolated and probably confined
to urban areas. QPF amounts near and east of I-29 are a bit either
side of 1-1.5 inches with HREF PMM suggesting pockets of up to 2-2.5
inches, more likely across NW IA. Given saturated soils as of late,
renewed issues with ponding of water and river rises will be the
more likely impact.

Synoptic Wind: Aforementioned deepening surface low to the west will
continue to provide for Advisory level wind gusts (45 mph or higher)
into the early evening before decreasing BL mixing should result in
a decreasing trend closer to sunset.

Tonight: After storms exit to our east toward the midnight hour, the
remainder of the overnight looks fairly benign.

Tuesday and Wednesday:  Vorticity ribbons pivot off the filling
upper low into midweek. This will bring occasional rain chances with
Wednesday currently appearing to be the focus as the main lobe
shifts east. With the main upper low overhead, Wednesday would be a
timeframe to monitor for slow moving storms capable of locally heavy
rain as well at least some potential for low topped funnels.

Thursday through Sunday: Transition to upper level northwest flow on
the backside of the upper level trough will bring seasonal
temperatures for the second half of the week with perhaps a few low
chances for a light shower.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1150 AM CDT Mon May 6 2024

A few aviation concerns over the period with the first being the
gusty southeasterly winds that will continue through the daytime
hours today. These will gradually weaken toward and after
sunset.

Other primary concern will be developing showers and
thunderstorms through the afternoon and evening hours. Initial
showers and storms are expected to develop along and west of
I-29 by as early as mid afternoon. These will be difficult to
time but have covered with a general -SHRA mention for now
although VCTS within this broader -SHRA field is certainly
possible. A more coherent line of thunderstorms is expected to
move from west to east through the second half of the afternoon
into the evening. Have timed this better -TSRA timing into the
TAF but will monitor for adjustments.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 7 PM CDT this evening for SDZ038>040-050-
     052>071.
MN...Wind Advisory until 7 PM CDT this evening for MNZ071-072-080-
     081-089-090-097-098.
IA...Wind Advisory until 7 PM CDT this evening for IAZ001>003-012-
     013-020.
NE...Wind Advisory until 7 PM CDT this evening for NEZ013-014.

&&

$$

DISCUSSION...Kalin
AVIATION...Kalin