505
FXUS63 KABR 090239
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
939 PM CDT Fri Aug 8 2025

.KEY MESSAGES...

- If we can overcome the warm air aloft, showers and thunderstorms
  are possible (40-60%) this evening through early tonight mainly
  for locations along and east of the James River through west
  central MN.

- There is a slight risk (level 2 out of 5) for severe weather
  mainly along and east of the Sisseton Hills. The main threats
  include large hail, wind gusts of 60-70 mph, along with a
  tornado or two possible.

- Across north central South Dakota Saturday afternoon, winds will
  gust 30 to near 40 mph out of the west.

&&

.UPDATE...
Issued at 939 PM CDT Fri Aug 8 2025

A Severe Thunderstorm Watch has been issued for Big Stone, Grant,
and Deuel Counties in eastern SD and west central MN. While storms
have not developed yet, there is the potential for a couple of
strong to potentially severe storms over those counties prior to
midnight.

UPDATE Issued at 628 PM CDT Fri Aug 8 2025

While the main surface trough/cold front is now over far eastern
SD, we still have several boundaries showing up on the radar. A
few showers and isolate thunderstorms remain possible outside of
far eastern SD and west central MN over the next 3 hours, but the
strongest look to remain mainly east in a sector of higher CAPE
and overall instability. Another area of concern will be south
central SD, with most of those storms remaining south of the
area.

&&

.DISCUSSION...
Issued at 314 PM CDT Fri Aug 8 2025

As of 230pm scattered to broken clouds cover much of the area with
the cold front just east of the James River with winds gusting
behind the front up to 25mph. The main concern will be the potential
for strong to severe thunderstorms east of the James River this
evening with a couple of possible scenarios that could play out.

By 00Z, the cold front is forecasted to be along the SD/MN border
with the upper level low spinning over MT/ND/Canadian border. This
puts the CWA in southwest flow aloft on the downstream side of its
trough. Low level convergence associated with the boundary and
ample shortwave activity aloft sets the stage for convection over
the region along and right behind the front. However, warm
temperatures at 700mb continue with temps of 14 to 16C which has
helped keep any convection from really firing up over the area
thus far. The HREF does indicates this cap eroding over this
evening per daytime heating of today and robust instability
building beneath it. So this leads to a couple of scenarios that
could play out. The first one is that the cap does erode and
convection fires up in a couple of places. One place either over
the James River Valley or more eastward in the form of clusters
and/or broken lines sometime between 23-03Z. The other location is
clusters of storms moving in from southwest SD, tracking
northeast, and moving in over portions of south central SD. With
this first scenario Cams (HRRR/HREF/NSSL- WRF/NAMNest) seem to
indicate these storm clusters/broken lines quickly growing upscale
into a more organized line, per a strengthening MCS and lower/mid
level jets. However exact location does vary between these models
as this could either occur near or along the SD/MN border or more
over west central MN with the bowing line of storms tracking
further eastward into MN. The other scenario is that the cap holds
later or is too strong for convection to fire up, therefore, we
really do not see much if any organized convection or it forms
much further east with really only clipping our MN counties. This
looks to be lower chance of this happening but not out of the
question.

If storms do fire up, there is ample amounts of moisture and
instability for storms to become strong to severe as MU/ML Cape is
on the order of 4000+ J/kg, highest along the SD/MN border and
eastward by 00Z. Values of 2000-3000 j/kg will be over the James
River Valley with values decreasing further west you go. Bulk shear
will be plentiful between 40-50kts out of the south which make sense
as storm mode would quickly form into a organized line as its
parallel to the front. Mid level lapse rates will be quite steep as
well. With most of the convection firing over the James River Valley
and westward, this looks to be more of an elevated risk, given the
post frontal nature, with large hail up to quarters to 1.50", and 60-
70 mph winds gusts. The higher end wind gusts of 70 would be if a
more organized line does form east of the James River. There is the
potential for a tornado or two especially over western MN for a
brief period right along the front as STP here is 2-4. Soundings in
this area show low level saturation, dry air aloft, and a curved
hodograph indicating a good amount of low level shear. Otherwise
post front, hodographs quickly turn to more of a straight hodograph
given the elevated nature. With the latest run of models and more of
an eastward extent of this severe threat, the SPC has adjusted the
slight risk (level 2/5) which now lies along and east of a line from
Sisseton to Huron and the marginal risk (1/5) stretching westward of
a line including Aberdeen to Chamberlain. There is an additional
slight risk area over portions of south central SD for large
hail/wind gusts of 60 due to those storms, mentioned above, moving
in over that area from teh southwest. The greatest tornado risk will
be over our west central MN including the counties of Big Stone and
Traverse in our CWA as a 5% chance within 25 miles of a point is
highlighted.

Heading into the weekend, this mid level low will continue to track
eastward over the northern CONUS/Canadian border and CAA over the
region. This will cause for an increase in winds Saturday, mainly
over north central SD with gusts up to 30kts. This mid low will then
track more northeastward early next week as a +PNA pattern sets up
with the ridge over the Pacific Ocean and trough over the Northern
Plains. This looks to be the pattern through early next week
ushering in quieter weather through the mid week. The ridge then
breaks down per several shortwaves moving over it and downstream
which may result in more of an active pattern once again by the end
of next week. Temps will run pretty seasonal in the 70s and 80s
through Monday with temps back in the 80s and 90s Tuesday and
onward, highest temps over central SD.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 628 PM CDT Fri Aug 8 2025

Terminals KABR,KATY,KPIR,KMBG

Showers or thunderstorms aren`t completely out of the question at
both ABR and ATY, but most likely at ATY around 0130-4Z when a
tempo for thunderstorms is included. Winds have shifted out of a
northerly direction behind the main cold front by 23Z Friday.
Expect winds to slowly shift out of the west to south- southwest
first at MBG/PIR from 03-09Z Saturday, and then PIR/ABR by 12Z,
and lastly ATY by around 15Z. Winds will be strongest over north
central SD (MBG) with gusts of 25-30kts in the afternoon.


&&

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

$$

UPDATE...06
DISCUSSION...MMM
AVIATION...06