478
FXUS63 KABR 200426 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1126 PM CDT Tue Aug 19 2025

.KEY MESSAGES...

- Heat index values will top out in the upper 90s to around 100
  degrees Wednesday and Thursday across central South Dakota.

- The passage of a low pressure system and cold front late
  Thursday afternoon through Thursday night will bring a 40 to
  70 percent chance of precipitation, with a marginal risk (1/5)
  of severe storms.

&&

.UPDATE...
Issued at 623 PM CDT Tue Aug 19 2025

The forecast remains on track this evening. No major changes are
planned.

&&

.DISCUSSION...
Issued at 230 PM CDT Tue Aug 19 2025

Weak wave overtopping a strengthening ridge that was responsible for
early morning central ND convection may support additional
redevelopment in eastern South Dakota this afternoon as we are
already seeing cumulus development along the Buffalo Ridge/eastern
Sisseton hills. Despite increasing heights on a whole, BUFKIT
profiles point to a high CAPE (2500+ j/kg) but very low shear
environment.

Will once again need to contend with fog in the morning. HREF and
several of its members all hint at fog development along and/or
east of the James by morning. Not a great consensus thus far, will
leave in inherited grids which have more coverage in comparison
to blends at this time.

For the upper level flow: A Four corners high, or more precisely a
ridge extending from it is the dominant feature Wednesday and
Thursday. That breaks down with an upper trough moving from central
into eastern Canada late in the week. This will shift the upper
level flow into more of a NW flow regime.

At the surface, the heat and humidity will not go anywhere in the
short term. The core of the warmest air aloft remains just to our
west until Thursday, folding over with the mid-level ridge. 700 and
850 millibar Temperatures will run at a standard deviation above
climatology by Thursday. That`ll be in stark contrast to the
standard deviation below climatology that can be expected Friday and
through the weekend. NBM heat index values top out at around 100 in
central South Dakota for a for both Wednesday and Thursday.

An inverted trough will extend northeast off a low that looks to hug
the South Dakota/Nebraska state line. This may provide the focus for
surface based convection Thursday, however will need to contend with
the warm temperatures aloft. A positively tilted shortwave will
provide ascent aloft as well. If convection remains wholly aloft, it
will be in a unidirectional sheer environment with stronger mid
level flow along the North Dakota/South Dakota state line with
weakening shear as we proceed south. There will also be a low level
jet that develops early Friday ahead of the boundary as the boundary
migrates southeast.

Regarding smoke aloft, RAP/HRRR models both bring in smoke late on
the 20th and persist through the remainder of the model runs. If
this lingers into Thursday, it could also negatively impact daytime
heating and thus the potential for surface based convection to break
the cap.

The rest of the forecast will deal with cooler temperatures, with
the NBM running 5-10 degrees below climo  and a significant drop in
humidity.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1125 PM CDT Tue Aug 19 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are expected to prevail through the next 24 hours.
However, KATY may still see some brief IFR/MVFR fog in the
morning prior to 15z.

&&

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

$$

UPDATE...20
DISCUSSION...07
AVIATION...20