563
FXUS63 KABR 190805
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
305 AM CDT Tue Aug 19 2025

.KEY MESSAGES...

- Pockets of patchy fog will expand over portions of mainly
  eastern SD and west central MN and slowly improve from daybreak
  through 10 AM.

- Heat index values will top out in the upper 90s to near 100
  degrees today and Wednesday afternoon over south central SD. A
  few locations are forecast to reach heat index values of 100 to
  104 degrees south of a line from Mission Ridge to Onida and
  Highmore Thursday afternoon.

- 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, or level
  1 out of 5, of severe storms.

&&

.DISCUSSION...
Issued at 303 AM CDT Tue Aug 19 2025

The 08Z surface map shows high pressure over Manitoba extending a
ridge over our forecast area. Low pressure was set up across the
intermountain west. Light winds remain in place under the ridge
today, with another round of early morning fog that is currently
more focused over portions of southeastern SD but will be expanding
at least patchy fog over much of eastern SD and west central MN by
daybreak before improving through 10 AM. The fog is not expected to
be as dense or cover as much of the area as Monday morning. Given
mainly dry weather and the surface ridge sliding east Tuesday, the
focus weather wise will be on temperatures. Dewpoints will remain in
the upper 60s to low 70s. These higher dewpoints and the
temperatures in the 90s over portions of central SD will result in
higher heat index values. Heat index values will top out in the
upper 90s to near 100 degrees today and Wednesday afternoon over
south central SD. A few locations are forecast to reach heat index
values of 100 to 104 degrees south of a line from Mission Ridge to
Onida and Highmore Thursday afternoon. We will continue to monitor
the trends and wait and see if any heat headlines will be needed. At
this point we will start advertising the potential in the HWO.

Upper-level low pressure over British Columbia starts to
develop and move east Wednesday evening into Thursday. This low
pressure will interact with the upper-level ridge, pushing the ridge
out of SD. An associated surface low pressure in Canada will start
to push a cold frontal boundary into SD, with models varying the
time of arrival slightly between late Thursday morning into the
early evening. The front will move over the state through the night
and into Friday morning. This frontal passage will most likely bring
precipitation and potentially storms with it as it moves through
SD. There is now a marginal risk of severe storms over much of the
forecast area for late Thursday afternoon into Thursday night.

The front will also bring colder air into SD, causing the
temperatures to start to lower into the weekend. Max temperatures
are currently forecast to drop down into the 70s and even the upper
60s over far northeastern SD by the weekend. Additionally, the
frontal passage will cause the winds to shift to be mainly from the
northwest through the weekend. There is the potential for wildfire
smoke to travel aloft along those winds and into the area.


&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1036 PM CDT Mon Aug 18 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail at KPIR and KMBG Tuesday. KATY and
KABR will see a period of MVFR/IFR fog and stratus Tuesday morning
before improving by 16z.

&&

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

$$

DISCUSSION...06/12
AVIATION...20