621
FXUS63 KABR 292336
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
636 PM CDT Fri May 29 2026

.KEY MESSAGES...

- The Northern Plains will see an active pattern, and chances
  for showers and thunderstorms are in place through the
  weekend and into the start of next week.

- Through Sunday evening, chances of 0.25" of rain or more is
  70-90% west of the James River. Chances of 0.5" of rain or
  more is 50-85%, highest along and west of the Missouri
  River. Amounts may be higher with any stronger storms.

- There is a Marginal Risk (Level 1 of 5) for severe weather
  Saturday evening into Saturday night across central and parts
  of north central South Dakota. Jones County, as well as
  parts of Lyman and Stanley Counties reach a Slight Risk (Level
  2 of 5). Damaging wind gusts of 60-70 mph and hail of 1" in
  diameter are the main threats. A tornado or two can not ruled
  out in the slight risk area.

- There is a Marginal Risk (Level 1 of 5) for severe weather
  Sunday, mainly along and west of the James River Valley.
  Damaging wind gusts of 60 mph and hail of 1" in diameter are
  the main threats.

&&

.UPDATE...
Issued at 601 PM CDT Fri May 29 2026

Just some minor changes to POPs. Will keep them a little low as
most of the returns are amounting to a trace to maybe a
hundredth or two.

See below for an update to the aviation discussion.

&&

.DISCUSSION...
Issued at 225 PM CDT Fri May 29 2026

Omega block pattern continues with a highly amplified ridge now over
east-central CONUS (return flow) with an upper level low over
Canada/New England and upper trough over the western CONUS by 00Z
Saturday. WAA at 850mb to surface will continue to be breezy out of
the southwest with ongoing open access to the Gulf as dewpoints are
ranging in the mid 50s to the mid 60s. This is shown well by RAP
1000-500mb RH as RH by this evening ranges between 80-90+% and will
continue through the weekend. At the surface, high pressure system
is off to our east over Indiana with a north to south oriented lee
trough/stationary front setting up to our west. With return
flow/moisture along with weak pulses of upper level energy here and
there tracking northward over the CWA from the gulf, CAMs continue
to show scattered rains showers here and there mainly along and east
of the Missouri River. Daytime heating may allow for weak
thunderstorms to occur with the possibility of pea size hail,
however, mid level lapse rates are rather weak, CAPE 500j/kg and
under, and no bulk shear. Through the overnight into Saturday
morning, the center the trough becomes a closed low where it will
track more northeast and over UT/CO/WY which will bring the chance
of thunderstorms over central to western SD (as CAMs indicate this)
while scattered rain showers continue east of here with better
moisture advection over the area and higher PWAT`s. Latest NBM
indicates pops of 50 to 75% west of I29 between 00-12Z Saturday.

Saturday morning through Saturday afternoon, return flow continues
at 500mb along with southeasterly flow/moisture at 850mb to surface
as dps are forecast to be in the mid 50s to lower 60s. 850mb to
surface, an elongated area of low pressure will extend from MT
through CO with one low spinning over MT/WY and one over CO by
Saturday afternoon with a northwest to southeast converging
line/frontal boundary from western SD through western KS with a
dryline west of here. This setup will bring ongoing scattered
showers and thunderstorms moving in from the south/southeast here
and there across the CWA. Storms during this time should stay below
severe limits through the early afternoon as CAPE will be under 1000
j/kg through the early afternoon, and lack of shear and lapse rates.

By 00Z Sunday, the upper closed low will be over WY with an embedded
negative tilted shortwave over eastern CO and western KS/NE where it
will track northeast and over the western half of Dakotas by early
Sunday morning. At the surface, this weakening low over MT and its
occluded front will be over southwestern SD through NE as another
area of low pressure will develop over KS/NE border and shift a bit
eastward by 12Z Sunday. So with this setup, NamNest, HiRes Cams, and
HRRR all indicate discrete cells turning into a north to south line
(or broken line) of storms, east/northeast of a dryline, over
western SD through western NE Saturday evening. It will then track
east and over our western CWA (central SD) between ~03-06Z where it
will continue to track east/northeast across the CWA. If a cold pool
develops, this outflow part of the storm will track southeast.

HRRR/HiRes FV3/NSSL WRF indicate the possibility of a bowing line,
however, the apex of the bow placement differs. For example, FV3
shows the bow more south of the CWA with HRRR more northward across
south central SD pushing eastward, and HiRES ARW further north. So
still uncertain on exact path for now. HREF 700-500mb lapse rates
will increase to 6-7C/km, highest over south central SD late
Saturday afternoon with SFC/MU CAPE increasing between 1000-2000j/kg
over central SD with the highest over far south central SD through
about 06Z as bulk shear increases to around 30-40kts by this time
along and west of the Mo River. 0-3 and 0-1 SRH is forecast to range
between 100-200m2s2 over central SD after 00Z Sunday. Due to this
setup SPC continues with a marginal risk (level 1/5) along and west
of a line from Mcintosh to Miller with a slight risk (level 2/5)
over the southern portions of Stanley, Jones, and western Lyman
(which is on the northern axis of better instability) Saturday
evening/overnight. The main threat will be large hail (size of
quarters), wind gusts of 60-70 mph (could be higher if a bow echo
forms) and the threat for a tornado or two (in the slight risk area).

By Sunday, winds aloft will be out of the south/southwest with the
850mb low over MT and tracking over MT/southern Canada by Sunday
evening with winds out of the southwest to southeast. Northwest to
southeast convergence over the western CWA along with ongoing low
level moisture, and some instability, isolated severe storms are
possible with hail up to quarters and wind gusts of 60 mph as the
spc has highlighted a marginal risk (level 1/5) along and south and
west of a line from Eureka to Watertown Sunday afternoon and
evening.

Mean QPF amounts 00Z Saturday to 12Z Monday ranges from 0.3 to 0.7"
west of the James River and highest along and west of the MO. 75th
percentile would be around 0.8 to 1.0". However, any stronger storms
will produce localized brief heavy downpours, increasing overall QPF
for any one location. With this upper low/trough pretty much hanging
out over the Northern Rockies, we will continue with chances of
precip off and on pretty much through most of next week. Temps will
be cooler for the weekend in the 70s and 80s through Monday, and
ranging in the 80s Tuesday through the end of next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 601 PM CDT Fri May 29 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions for KABR/KATY/KMBG initially, but with continued
rain showers (mostly light), however gradually look for a
lowering of Ceilings overnight into Saturday. Lowest CIGS are
expected for KPIR, which could also experience convection
Saturday afternoon. Winds primarily from the southeast.

&&

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

&&

$$

UPDATE...07
DISCUSSION...MMM
AVIATION...07