560
FXUS63 KFSD 061139
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
639 AM CDT Mon May 6 2024

.KEY MESSAGES...

- Wind Advisory in effect for most of the forecast area today.
  Gusts 40 to 50 mph expected.

- A few strong to severe storms are possible this afternoon and
  evening, with the greatest severe threat currently focused
  along and south of the Missouri River and US Highway 18
  corridor. Locally heavy rainfall is possible.

- Periodic rain chances continue for much of the upcoming week
  into next weekend, with highs in the 60s to lower 70s.

&&

.DISCUSSION...
Issued at 405 AM CDT Mon May 6 2024

CURRENTS: Low pressure continues to deepen this morning in the
Rockies, with a strong jet tracking northward across the Plains this
morning. Showers and isolated thunderstorms are already developing
across the central and western portions of SD and NE forced by the
WAA and nose of the jet. Expect this area to continue to move off to
the east through the morning hours. Additionally, surface pressure
gradient is tightening with the deepening low pressure and coupled
with the LLJ, have already started to see south/southeasterly winds
increasing as of 3 AM CDT/08z. This trend also continues through the
morning hours. WAA and the aforementioned south to southeast flow is
keeping temperatures more mild than the last couple of nights, still
in the upper 40s and 50s.

TODAY AND TONIGHT: A couple rounds of precipitation expected today,
with the potential for strong to severe storms and locally heavy
rainfall during the afternoon and evening hours. Otherwise, we`ll
warm into the 60s and lower 70s with lots of cloud cover around.
Synoptic winds continue to increase, with gusts 40-50 mph as the
pressure gradient tightens and the LLJ strengthens overhead. Wind
Advisory is in effect for much of the area from daybreak through
this evening.

For the first round of precipitation, we`ll continue watching the
developing showers/storms to the west this morning as they move to
the east and expand in coverage. Instability for this area of
precipitation remains at or below 300 J/kg across most guidance, so
severe weather is not expected. This line of showers/isolated storms
moves east through the early part of the day, reaching the I-29
corridor by the early afternoon, becoming more sparse as it does so.

Attention turns back to the west by early afternoon with the cold
front across western NE and points south. Better instability and
forcing remains off to the south; however, 06.00z guidance has shown
a bit of an increase to the instability over our western forecast
area this afternoon, tracking east during the evening hours. MUCAPE
values still look to be around/less than 1500 J/kg ahead of the
front - soundings along with ensemble guidance has been continuing
to keep values at or less than 1000 J/kg, so a bit lower confidence
in broader deterministic models trending upward with instability at
this time (even when accounting for the different models running
with most unstable vs. surface based CAPE). Think that cloud cover
and limited warming will help to temper instability - especially
surface based. As with our last few events, environment leans toward
a high shear/low CAPE situation, as our shear values exceed 40
knots. Although discrete cells are expected initially, strong shear
parallel to the front supports quick upscale and linear growth. Mid
level lapse rates continue to be steep, 7 deg C/km or more. Thus,
think main threats will be hail to ping-pong ball size with discrete
cells, and transition to a wind threat with gusts to 70 mph as the
line evolves. Risk is low, but can`t rule out a tornado or two given
SRH values around/above 100 m^2/s^2. Greatest severe risk remains
between 3-9PM, although a stronger storm could develop as early as 1
PM if some of the quicker hi-res guidance is realized.

Locally heavy rain continues to be a threat particularly for areas
along/east of I-29 where moisture advection is the greatest.
Additionally, PWAT values for this area climb to around 1.25", in
the top 10% or less of climatology for this time of year.
Probabilities of 1"/hr rainfall rates are low, less than 10%. Total
accumulations through tonight range from less than 0.25" west of the
MO River in south central SD to over 1" in northwestern IA and
southwestern MN. Saturated soils due to recent rainfall could lead
to isolated areas of flash flooding in urban and low lying areas
east of I-29 (greatest concern for northwestern IA). Outside of this
area, ponding is expected.

With strong to severe storms possible later today, stay up to date
with the latest forecast. Have multiple ways to receive warnings,
know your severe weather plan, and be prepared to put it into action
should a warning be issued for your location.

Otherwise, main line of storms exits the eastern CWA by the early
overnight. Isolated showers may redevelop west of the James through
the overnight hours. Lows fall into the 40s and lower 50s.

TUESDAY THROUGH THURSDAY NIGHT: Mid level low lingers, meandering
and wobbling across the north central Plains through the work week.
Models show varied solutions in the timing and evolution of the mid
level low (breaking it down, splitting the low in two, shearing it
off into more zonal flow with multiple waves, just to name a few).
Therefore, expect mostly dreary conditions with periodic rain
chances through Friday night. Highs in the 60s to lower 70s with
lows in the lower/mid 40s - both of which are near average values
for early May. Breezy conditions are expected as well, with the
strongest winds expected Wednesday and Thursday with CAA and
stronger flow aloft paired with a slightly more compressed surface
pressure gradient.

FRIDAY THROUGH THE WEEKEND: Stagnated mid level low slides out
Friday morning, with another trough quickly on its heels. This will
keep rain chances over the area through the end of the week and into
the early part of the weekend, with this trough racing south across
the northern Plains and upper Midwest through the day on Friday.
Models diverge on handling this trough, with the GFS keeping this
low overhead and stagnate through the weekend while the ECMWF is
much more progressive bringing a series of waves through over the
weekend. Regardless, periodic isolated to scattered showers return.
Temperatures remain a few degrees either side of normal.
Northwesterly winds will be breezy at times.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 630 AM CDT Mon May 6 2024

VFR conditions continue to deteriorate this morning as stratus
lifts up from the southwest. MVFR/IFR conditions prevail through
much of the day into tonight as stratus lingers and
showers/storms move in. VFR conditions return toward the end of
the period.

A couple of rounds of showers and storms are expected today. The
first area is sliding east across central SD, and should reach
the James Valley by 06.15z. This continues moving east through
the early afternoon. Second area of showers and storms develops
by 06.20z in south central SD/north central NE, racing east
through the evening hours. Stronger storms could produce
damaging winds, large hail, and locally heavy rain. Showers and
storms diminish from west to east through the late evening and
early overnight.

Final aviation concern will be in the increasing south to
southeast winds this morning, remaining strong through the
evening hours. Winds could gust above 40 knots, with the
strongest winds across south central SD. Elsewhere, gusts 30 to
40 knots elsewhere. Expect winds to taper off late this evening
into the overnight. Although the low level jet will be
strengthening today, strong gusts mixing down and LLJ oriented
the same as surface winds should limit LLWS concerns.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory from 10 AM this morning to 7 PM CDT this evening
     for SDZ039-040-054>056-060>062-065>071.
     Wind Advisory until 7 PM CDT this evening for SDZ038-050-052-
     053-057>059-063-064.
MN...Wind Advisory from 11 AM this morning to 7 PM CDT this evening
     for MNZ071-072-080-081-089-090-097-098.
IA...Wind Advisory from 11 AM this morning to 7 PM CDT this evening
     for IAZ001>003-012-013-020.
NE...Wind Advisory from 10 AM this morning to 7 PM CDT this evening
     for NEZ013-014.

&&

$$

DISCUSSION...SG
AVIATION...SG