921
FXUS63 KABR 181833
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
133 PM CDT Tue Aug 18 2026

.KEY MESSAGES...

- A Marginal Risk (level 1 out of 5) for severe weather has been
posted for along and south of the I-90 corridor late this afternoon,
evening and into the overnight hours. The main threats will be hail
around 1" diameter and winds up around 60 mph.

- A Marginal Risk (level 1 out of 5) for severe weather has been
issued for between the Missouri and James valley regions Wednesday
late afternoon and through the evening hours. Hail around 1"
diameter and damaging winds are the main threats.

&&

.DISCUSSION...
Issued at 132 PM CDT Tue Aug 18 2026

We are tracking a weak wave moving through southeast North Dakota
headed into far northeast South Dakota and western Minnesota. Just
some ACCAS and light radar returns. The rest of the area is
marginally unstable in NAM/HRRR BUFKIT profiles for the afternoon.
There is a broad trough overhead, and an upstream wave that is
expected to move south of the area this afternoon. Generally, cant
rule out a storm or two in the heat of the afternoon so broadly
added some low POPs.  Profiles are mainly dominated by skinny CAPE
and unidirectional shear. A wave that moves down across central
South Dakota later this evening and overnight provides a better
impetus for convection, hence the marginal risk outlined by SPC.

Activity diminishes/moves out of the CWA during the morning
Wednesday, with another wave coming down from the northwest late.
Again we`re still under this broad upper trough centered to the
northeast, and as such marginally unstable through the day as well.
Yet again, profiles are defined by skinny CAPE and unidirectional
shear.

The upper ridge out west gradually increases in amplitude and
strength, with increasing heights across South Dakota
Thursday/Friday we we`ll begin to say with more consistency and
confidence in dry conditions most of the area Thursday and across the
Dakotas Friday. Thursday will see another trough passage not too
dissimilar to yesterday`s but with warmer air aloft and lower
dewpoints to limit instability. Fridays temperatures will be
slightly cooler in comparison  to Thursday on the backside of the
front/south end of high pressure.

The upper ridge crests over the region during the weekend. 700mb
temperatures increase to about a standard deviation above climo.
This warm air collapses with the passage of an upper wave late
Sunday. NBM POPs early Sunday align with the GFS brining in some
ACCAS/mid level convection. The wave that passes through doesn`t
break down the ridge permanently, with a rebound of the upstream
ridge for the first half of next week. This is trending temperatures
back above normal though right now about 5-10 degrees for next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 132 PM CDT Tue Aug 18 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions for all terminals.  Cant rule out a storm,
particularly near the KPIR terminal, but for KABR/KMBG/KATY the
probability is too low for inclusion in this set of TAFS.

&&

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

&&

$$

DISCUSSION...07
AVIATION...07