938
FXUS63 KABR 270102 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
802 PM CDT Sat Jul 26 2025

.KEY MESSAGES...

- Hot and humid conditions to continue into Monday. Heat index
  values of 100 to 105 degrees are expected across central and
  northeast South Dakota into west central Minnesota Sunday
  afternoon and evening.

- There is a 30 to 50 percent chance of showers and storms over
  central and northern SD tonight. There is a Slight Risk, or
  level 2 out of 5, of severe storms capable of producing strong
  winds well in excess of 60 mph and hail up to around 1 inch in
  diameter west of a line from Britton to Aberdeen to Onida.

- There is a Marginal Risk, or level 1 out of 5, of severe storms
  late Sunday afternoon into Sunday evening across eastern SD, and
  across the entire forecast area Monday into Monday night. A few
  of the strongest storms will be capable of producing hail to 1
  inch in diameter and winds to around 60 mph.

&&

.UPDATE...
Issued at 759 PM CDT Sat Jul 26 2025

Allowed the heat advisory for today to expire. Temperatures and
heat indices will continue to fall through the evening.

UPDATE Issued at 609 PM CDT Sat Jul 26 2025

Adjusted hourly pops across central SD this evening to account for
the storms that are already forming west river. Otherwise, the
forecast remains on track this evening.

&&

.DISCUSSION...
Issued at 234 PM CDT Sat Jul 26 2025

At 2 PM CDT, skies are mostly sunny and temperatures are warming
through the 80s and 90s, with a few locations out over central and
south central South Dakota already nosing up close to 100F degrees.
Winds are south around 10 to 20 mph with gusts up to 30 mph. A few
elevated thunderstorms persist early this afternoon over far
northeast South Dakota into west central Minnesota.

The upper level flow pattern remains largely unchanged through
Sunday night, consisting of a hot sub-tropical upper level ridge
over the CWA that breaks down when a western CONUS/west coast upper
level trof propagates over into southern Canada/Great Lakes region
next week.

Notable shortwave energy out over the inner-mountain-west will move
across the region later this evening/overnight. As a result, at
least scattered-coverage thunderstorms are forecast over and west of
the Missouri River valley region of the CWA this evening into the
early overnight hours. Thunderstorms developing within lee-of-the-
Rockies/Black Hills lee-side surface trofs/surface lows again this
afternoon/evening, the boundary layer should be quite deep with
temperatures reaching or exceeding the century mark across central
South Dakota (inverted-V soundings with severe thunderstorm wind
gusts at a premium this evening/tonight). 700hpa temperatures
between +12C and +14C reside across the western third of forecast
zones lending credibility to forecast mid-level lapse rates at or
above +9C/km. However, temps that warm also mean there is some mid-
level thermal capping to overcome before CI can happen. Models still
prog a low level jet to develop and be near/over the northern half
of the CWA for additional nocturnal source of forcing/fuel to keep
ongoing storms going. Tonight`s progged deep layer shear is between
30 to 45 knots, and instability potentially >3500J/kg CAPE. In
addition to large hail and potentially very strong winds, 0-1km
shear increases to over 30 knots tonight (by 03Z). Wondering if
tonight`s convective evolution could include the kind of 0-3km shear
that supports squall-lines with embedded supercells for that "qlcs"-
type TOR potential. LCL heights are rather high, but are progged to
be lower closer the Dakotas border this evening. Also, 0-3km cape in
the Rap is pretty much non-existent right now for this
evening/overnight. Would like to see that parameter lighting up
(>50J/kg needed), too, before getting too concerned about TOR
potential late this evening over north central South Dakota. The
western/northern counties of the CWA are in a slight risk (level 2
out of 5) for the potential of a few storms capable of hail up to an
inch and thunderstorm wind gusts well in excess of 60 mph later this
evening/overnight.

With the sub-tropical heat ridge remaining over the region this
afternoon through Sunday, high-end heat (temps 5 to 15 degrees above
normal) is anticipated across the CWA this afternoon/evening and
again Sunday afternoon/evening, when enough low level moisture is
expected to be around to support heat index values at or above 100
degrees. In order to account for corn sweat, utilized NBM75th
percentile for a second consecutive day to nudge forecast dewpoints
up 2 or 3 degrees. The Heat Advisory for this afternoon/evening
remains in effect until 8 pm CDT. The Heat Advisory for Sunday
afternoon/evening has been expanded up into northeast South Dakota
and over into west central Minnesota (including the Coteau this
time), and remains in effect from 1 pm CDT to 8 pm CDT Sunday.

GOES Geocolor satellite imagery depicts, faintly, a layer of smoke
aloft over the region. The latest complete 84-hour run of the RRFS
for smoke suggests that this smoke aloft (vertically-integrated
smoke) will persist over the region through Sunday (if not longer).
Still not seeing all that much for near-surface smoke. Hopefully,
this round of smoke will remain aloft and mainly result in slightly
reduced direct insolation and a milky gray appearance to the this
afternoon and Sunday.

There will be a slow-moving frontal boundary working south across
the region from Sunday through Monday morning, resulting in a wind
shift from these hot/humid southerly, return flow winds to more of a
north or northwesterly post-frontal wind as surface high pressure
gradually builds down over the region. There are currently
thunderstorm chances both Sunday and Monday; Sunday across the far
eastern forecast zones for any late afternoon/early evening
thunderstorms that may be able to overcome the warm mid-level
thermal capping inversion in place; Monday for what, presumably, is
expected to be an active EML (despite post-cold frontal low level
CAA and dry air advection within the boundary layer). Both days,
deep layer shear within the cloud bearing layer is expected to be at
a premium, with more than adequate instability/mid-level lapse rates
to support strong to severe thunderstorms. There is a marginal risk
(level 1 out of 5) for severe thunderstorms across the far eastern
forecast zones Sunday afternoon/evening and over the entire CWA on
Monday, with hail up to an inch in diameter and thunderstorm gusts
over 58 mph. Monday`s potential rainfall also carries with it the
potential for training/excessive-rain-producing thunderstorms.

The upper level ridge repositions westward, as western CONUS upper
level troffing propagates/relocates to over the Great Lakes
region/east coast from Monday through Thursday of next week. By
Friday, models are trying to shift the upper ridge back to over the
nation`s mid-section. Monday through Thursday, with northwest flow
over the region, conditions will be a bit more stable/cool/dry in
the boundary layer. After Monday/Monday night, thunderstorm chances
largely become a function of how often convection can develop out
over the northern high plains each afternoon and then organize/ride
the instability gradient that will extend southeastward from
Montana/Wyoming into South Dakota/Nebraska, potentially clipping
(mainly) the west river forecast zones of this CWA. 850hpa thermal
progs and S.A. table standardized anomalies remain, overall,
unchanged in their depiction of temperatures during much of next
week; some 5 to 15 degrees below normal, resulting in readings in
the mid 70s to low 80s.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 609 PM CDT Sat Jul 26 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are expected to prevail through Sunday afternoon.
Thunderstorms may move near KPIR and KMBG this evening. Added in
some prob30 groups for KPIR for now.


&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM CDT /noon MDT/ to 8 PM CDT /7 PM MDT/
     Sunday for SDZ006>008-010-011-017>023-033>037-045-048-051.

MN...Heat Advisory from 1 PM to 8 PM CDT Sunday for MNZ039-046.

&&

$$

UPDATE...20
DISCUSSION...10
AVIATION...20