550
FXUS63 KABR 110753
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
253 AM CDT Sun Aug 11 2024

.KEY MESSAGES...

- Temperatures will continue from 5 to 15 degrees below average
  today and 5 to 10 degrees below average for Monday.

- There is a 30-75% chance of showers and thunderstorms today through
  through early Monday, with the highest chances of precipitation over
  central South Dakota.

- There is a marginal risk (1/5) for strong to severe storms over
  south central South Dakota this afternoon and evening. Main threats
  include hail, up to the size of quarters, and 60-70 mph wind gusts.

- A general warming trend is expected with seasonal/near average
  temperatures for the middle to latter half of next week.

- Additional chances for moisture in the form of thunderstorms run
  from late Tuesday through early Thursday. Severe weather potential
  exists but with high uncertainty on timing/intensity/coverage of
  storms at this time.

&&

.SHORT TERM /TODAY THROUGH MONDAY AFTERNOON/...
Issued at 252 AM CDT Sun Aug 11 2024

As of 2am satellite imagery shows mid to high clouds, per northwest
flow, quickly exiting the area with more clouds off to our west and
northwest. Temps are ranging in the upper 50s to the lower 60s.
Water vapor imagery indicates the main shortwave over the Northern
Rockies with RAP/HREF showing this wave will continue southeast and
over the CWA this afternoon/evening. On the PVA side of the wave, a
surface low will accompany it and track southeast, with the center
of the low forecasted to be over southwestern SD by this afternoon
and into NE by this evening. On the eastern side of this low an
inverted surface trough will setup over western SD this morning and
over much of central SD this evening. RAP 1000-500mb RH indicates an
increase in moisture with this system as it tracks southeast with
the highest humidity over central SD. HREF PWAT at 00Z Monday ranges
from 0.87 over far northeastern SD, up to 1.3" over south central
SD. NAEFS indicates this is about 2 standard deviations above climo
for central SD.

With this setup short term models indicate scattered showers and
thunderstorms moving in over central SD ~early to mid morning with
the moisture spreading southeastward through this evening with the
system. Precip is forecasted to diminish northwest to southeast over
the CWA tonight as a high moves in behind the low. WPC has a
marginal risk (5%) of excessive rainfall mainly over central SD
where we see this excess moisture. Probability of 24hr rainfall over
0.50", ending Monday at 12Z, ranges from 50-75% around and west
river. Prob of 1.00" is 40-45% over south central SD.

As mentioned in the previous discussions, HREF/RAP keeps CAPE well
below 1000 J/kG, however, shear is still ranging between 30-40kts
over south central SD this evening along with mid level lapse rates
of 6C/km. 2-5 UH>75m2s2 paintballs still indicate the possibility of
more organized convection that could brush our south central CWA
(closer to the low/trough enhancement) with most of the threat
staying southwest of the CWA. RAP/EC soundings show an inversion at
700mb over most of the CWA but then looks to break a bit over south
central SD. With this threat, the SPC has a marginal risk (1/5) for
severe thunderstorms in this area for this afternoon and evening
with main threats including up to quarter sized hail and 60mph
gusts. HRRR/HiRes do show these cells merging into more of a
linear/bow system, with the northern extent of this possibly over
our south central CWA. If this occurs, 60-70+mph gusts would be the
main threat.

HRRR Smoke model indicates smoke aloft this morning continuing
through the day for much of SD, excluding far northeastern SD. With
the lower clouds today, temperatures across the area are forecasted
to range in the 70s and lows in the mid to upper 50s. Similar temps
expected for Monday.

&&

.LONG TERM /MONDAY EVENING THROUGH SATURDAY/...
Issued at 252 AM CDT Sun Aug 11 2024

A little better consistency between long term deterministic guidance
with respect to flow aloft this morning. The upper pattern is
dominated by ridging early on, though 700mb warm advection early
Tuesday could still result in weak convection ahead of the upper
ridge axis. That ridge axis moves overhead mid-day Tuesday, with a
southwest flow shortwave riding up over the ridge for mainly
western/central South Dakota Tuesday afternoon. That translates into
the eastern CWA overnight with a more pronounced trough coming into
the western portions of the state. This trough will enhance mid
level flow and provide support for potential convection into the day
Wednesday with NBM CAPE showing a narrow axis of higher values
(about 1000-1500 j/kg) running up the James valley. Still, some
uncertainty with respect to surface features with the Canadian
showing the more favorable trough placement with respect to the NBM
instability, with the surface features more towards central SD in
the GFS/EC. Again, still some fine details to work out as the GFS
axis of instability is back towards the Missouri valley. Peak shear
is around 35-45kts in the GFS as well. Additional uncertainty exists
with 700mb temperatures potentially on the warm side, between +9 to
+13C. The upper trough may linger into Thursday as well, with the
far eastern CWA CWASP at around 60%.

As for temperatures, not much has changed with fairly good
confidence. The highest uncertainty is during the day Thursday with
timing of the front, and weak cold advection possibly enhancing
mixing giving us the potential to overachieve with the NBM
deterministic close to the 75th percentile. Otherwise readings should
run right around climatology for early to mid August.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1147 PM CDT Sat Aug 10 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail for much of the TAF period, as dry low
level air from the slowly departing high continues to remain over
the area. Over central SD, a low pressure trough will move into
the area on Sunday morning and be the focus for some shower and
potential thunderstorms from late morning through early evening.
The best chance for showers is at KPIR, so they continue to show
the showers in the TAF. Will need to watch that area for stronger
storms and potential addition of thunder to the TAF.


&&

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

$$

SHORT TERM...MMM
LONG TERM...Connelly
AVIATION...SRF