074
FXUS63 KABR 121918
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
218 PM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Cooler temperatures continue for the weekend with highs in the 60s
to low 70s through the start of next week, with the possible
exception of a brief warmup to near-normal on Monday.

- There is a 15 to 30% chance of light rain and weak thunderstorms
late tonight through Sunday morning. Any rainfall amounts will be
light, from a trace to a few hundredths.

- Confidence is high on widespread rain and perhaps weak
thunderstorms Monday morning through Monday evening. There is a 60
to 80% chance of rainfall exceeding half an inch and 20 to 50%
chance of exceeding one inch of rainfall.

&&

.DISCUSSION...
Issued at 217 PM CDT Sat Sep 12 2026

Elongated area of high pressure stretching from the Dakotas and
northwestward into Canada will bring overall dry weather for the
rest of the afternoon continuing through late this evening. However,
above the surface high a belt of stronger zonal to slight northwest
winds aloft (60-80kts, highest ND/SD/MN border) on the southwestern
side of the large upper level low over east-central Canada (and
within a northwest to southeast oriented shortwave circling around
it over ND/MN) could be enough to generate some spotty to bands of
elevated rain showers overnight through Sunday morning. Several of
the CAMs do show these potential bands highlighting portions of
north central/northeastern SD/ND border and an area over south
central to east central SD. Latest NBM pops really only had pops
over south central so blended in ECAM to the mix to increase
coverage and pops for these areas, especially with what HRRR/REFS is
indicating. The caveat to this is the drier air at the lower levels
from this high as EC/RAP soundings show this. Due to this, QPF is
expected to be light with any rain potential up to a couple
hundredths at most. Not much in the way of MUCAPE overnight but bulk
shear will be around 50kts, however, mid level lapse rates are weak.
No severe weather is anticipated but cannot not rule out weak
thunderstorms over south central/east central SD as HREF Z>40dbz
does highlight this potential where more convective cells are
possible. Any heavier rain shower/storm will lead to higher QPF.

An upper level trough originating from the PacNW will track east and
northeast across the Northern Rockies through the Northern Plains
and into Canada Monday morning through Tuesday morning along with
its surface low/cold front. This wave and its low is forecast to
deepen to around 998mb over ND/Canada border Monday
afternoon/evening. GEFS is a bit further north and a few millibars
deeper (996mb) than the EC at this time therefore a bit lower
confidence in exact track and intensity for now. With the region
within the PVA of the UL wave in southwest flow and east of the sfc
low with low level winds out of the south/southeast, this provides
lift aloft and also ushers in moisture as dewpoints will increase
into the 60s and PWAT values will increase to around 1.2 to 1.6"
ahead of the cold front within the warm sector. Highest PWAT values
are around the 99th percentile for this time of year and 2-3
standard deviations above climo per NAEFS. With this setup and
moisture, models seem to be pretty consistent leading to higher
confidence on widespread rain moving in over central SD late early
Monday morning (pops 80%+) with the rain spreading east and
northeast and over the entire CWA by Monday morning through the
afternoon (80-100% pops along and east of Mo River). As the
low/front tracks east/northeast, rain will diminish west to east
across the CWA Monday afternoon over central SD with the last of the
rain exiting the eastern CWA Monday evening. Wind shear of 40kts
will be present, however, the better instability looks to remain
south and southeast of the region, therefore, no severe weather is
anticipated for now with just the potential for weak thunderstorms
given this shear and higher winds aloft and marginal instability.
Looking at the 06Z run of the ensembles, ENS mean QPF ranges from
0.3-0.7" (highest over eastern/southeastern SD) while GEFS is drier
given the more northern track with values of around 0.2-0.4" for the
24 hours ending at 06Z Tuesday. NBM probability of rainfall half
inch or more is 60-80% and one inch or more 40-50%, with the inch
prob mainly over northeastern SD/MN. High end scenario (wetter/more
southern track of low), rainfall would be between 1-2" and low end
scenario (northern track/drier) would be under a half inch.

With the passage of the cold front and steepening of the low level
lapse rates, winds will increase Monday over central SD early and
spread eastward with the front with gusts of 30-40kts by late
morning/afternoon. The cooler airmass overhead will continue through
the rest of the weekend with temps about 5-10 degrees below normal
for this time of year and highs overall in the 60s Sunday. Warmer
air per return flow on Monday will lead to warmer temps mainly west
of the James River with highs across the CWA in the upper 60s to
upper 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1207 PM CDT Sat Sep 12 2026

Terminals KABR,KATY,KPIR,KMBG

Mid to high based clouds continue to track eastward with increased
cloud cover over the region this evening through tonight as a
shortwave tracks across the area. VFR cigs are overall forecast
through the end of the TAF period. With this shortwave, there is
an isolated threat of spotty to bands of light rain (and perhaps
weak thunderstorms) early Sunday morning possibly affecting
KPIR and KABR at this time and affecting KATY after 10Z. Little
if any QPF is expected per dry low levels as a high pressure
remains dominant. Winds will continue out of the north and
northwest and switching to east/northeast for Sunday. Will make
adjustments to TAFs as needed.

&&

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

&&

$$

DISCUSSION...MMM
AVIATION...MMM