169
FXUS63 KABR 140521
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
1221 AM CDT Wed Aug 14 2024

.KEY MESSAGES...

- Chances for showers and thunderstorms (30 to 45 percent) across
  central South Dakota tonight, then chances increase (45 to 80
  percent) across the entire area Wednesday and Wednesday night.

- There is a Marginal Risk (level 1 of 5) for severe storms across
  the entire area late Wednesday afternoon and Wednesday evening.
  Large hail and strong wind gusts are the main threats.

- Lingering showers and thunderstorms Thursday (30-50%) will taper
  off from west to east Thursday night.

&&

.UPDATE...
Issued at 847 PM CDT Tue Aug 13 2024

Mid-level deck moving across the CWA currently may be bringing a
few sprinkles (based on radar) between the James and Missouri
rivers, but still expecting better precip potential to ramp up
later tonight and closer to 12Z. Did not make any changes to PoPs
for the overnight period. Made a few adjustments to sky cover
based on satellite trends, but otherwise, no major changes to the
forecast for the overnight hours.

&&

.SHORT TERM /THIS EVENING THROUGH WEDNESDAY NIGHT/...
Issued at 306 PM CDT Tue Aug 13 2024

Upper level ridging will get pushed east tonight ahead of an
approaching trough. A leading shortwave will swing across the CWA on
Wednesday, followed by the main trough and additional energy
Wednesday night.

At the surface, the region will be between high pressure to the east
and low pressure approaching from the west. Will see increasing
chances (30 to 45 percent) for shower and thunderstorm development
across central South Dakota during the overnight hours, then across
the entire CWA (45 to 80 percent) Wednesday and Wednesday night. The
best instability (1700-2200 J/kg) will be confined to south central
South Dakota Wednesday afternoon, but 30 to 45 knots of bulk shear
across the entire area will aid in some strong to severe storms late
Wednesday afternoon into Wednesday evening. The Storm Prediction
Center has highlighted the entire area with a Marginal Risk, with
large hail and strong wind gusts being the main threats with the
stronger storms. The precipitation will exit the area to the east
around or shortly after midnight.

Low temperatures tonight will be in the mid 60s. High temperatures
on Wednesday will be in the 70s to lower 80s. Lows Wednesday night
will be in the lower to mid 60s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 306 PM CDT Tue Aug 13 2024

The low pressure that will be impacting the weather in the region
will be moving out Thursday/Thursday evening and will be taking most
of the precipitation with it. After it moves out, a high pressure
will start to build into the area Friday evening/Saturday morning.
There looks to be the chance for occasional storms (10-20%) to
develop along the edges of the high pressure into next week.

200-300mb levels in the models show the area of lower pressure
moving over and then through SD Thursday into Friday morning. 700
and 850 mb levels show a lot of moisture with this low. The question
will be where this low tracks as it moves into eastern MN and where
the wrap around moisture and lift on the back side of the low will
be. Most ensembles show a stronger low moving into eastern MN with
precipitation wrapping around into northeastern SD. However, about
25% of the ensemble members show the low as much broader and weaker
over lower MN, leading to a larger swath of lower precipitation
chances over north central and northeastern SD. There is a 20%
probability of seeing a quarter of an inch of rain fall during the
day on Thursday, but most locations look to see below a tenth of an
inch (70% chance). Temperatures still look to remain 4 or so degrees
below normal.

After the low moves east, the upper levels show a ridge starting to
build into the area Friday evening/Saturday morning, and it stays
over the region through the forecast period. 700 mb moisture starts
to dry out with this ridge overhead, however, 850 mb still have
moisture over the area. 500mb has areas of potential vorticity
moving along the edge of this ridge as well as pockets of 850 warm
air advection and cold air advection. These forcings, along with
the moisture at 850mb, provide areas where precipitation could
develop over this time period. With the uncertainty of the timing
of these pockets, the confidence is low on the locations/timing
these storms could occur. The best chances (15-20%) would be
during the afternoon and evenings where diurnal heating could
affect the pockets as well. Looks like there will be enough shear
(30 to 35 kts)on the edge of the ridge for stronger storms,
however, the strongest instability, of 1000 to 1500 J/kg, is
southwest of the area of shear in southwest SD and western NE.
Temperatures during this time will start to warm to near normal
values around the mid-80s.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1220 AM CDT Wed Aug 14 2024

Terminals KABR,KATY,KPIR,KMBG

MVFR/IFR CIGs are forecast to overspread the region by morning, with
areas of SHRA/TSRA as well. Areal coverage and placement of
shower/storm clusters are a bit uncertain, but signs point to better
coverage during the afternoon/evening hours. Any heavier downpours
may produce MVFR/IFR VSBY at times if they manage to move over a
TAF site.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

UPDATE...TMT
SHORT TERM...Parkin
LONG TERM...Vernon/SRF
AVIATION...Connelly