079
FXUS63 KABR 210144 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
844 PM CDT Sat Jun 20 2026

.KEY MESSAGES...

- Widespread rainfall is expected this evening through the day
  Sunday with the bulk of the rain falling over central South
  Dakota. Probability of exceeding 1" of rainfall is 75-90%
  along and south of a line from Eagle Butte to Highmore with a
  40-60% chance of exceeding 2" for this area. Potential
  rainfall amounts drop off dramatically with little if any
  expected east of a line from Aberdeen to Watertown.

- A faster moving system will bring additional moisture to the
  region Monday evening through Tuesday evening. Probability of
  rainfall amounts exceeding 0.25" is 50-80% over portions of
  north central through northeastern SD into west central MN.
  Severe weather is not anticipated.

- Temperatures remain near to slightly below normal through
  next week. Coolest day being Sunday at 5 to 20 degrees below
  normal.

&&

.UPDATE...
Issued at 840 PM CDT Sat Jun 20 2026

Scattered light rain showers/sprinkles across the western CWA
this evening. Adjustments to PoPs were made earlier this evening
to account for a bit further north and eastward development than
previously forecast. Otherwise, not much activity in our CWA
now, but more coming in from southwest SD. Models still
suggesting an uptick in coverage of showers/storms later tonight
into Sunday morning as shortwave energy from WY approaches.

&&

.DISCUSSION...
Issued at 143 PM CDT Sat Jun 20 2026

Looking at the synoptic setup, west to slight northwest flow
continues aloft as the axis of the ridge is along the MT/WY and
Dakotas border. Interesting pattern sets up tonight through Sunday
with two closed lows ongoing to our northeast and northwest over
Canada with the slight ridging pattern continuing over the Northern
Conus/Canadian border in between these two lows. The ridge breaks
down with more of a zonal flow over SD. Within this pattern a
shortwave, with several embedded pulses, will move from the
Intermountain west and track eastward across the region through late
Sunday night with the CWA on the backside of this wave by Monday
morning.

The start of the rain is forecast to move in from the west over
south central SD with CAMs indicating this either late this
afternoon or early evening and spreading over north central SD
through tonight with the bulk of the widespread rain continuing over
much of central SD through Sunday. A slight shift eastward with the
wave on Sunday may bring some light rain over portion of the James
Valley and east central SD. Model soundings at KPIR indicate a
completely saturated profile by 06Z and KMBG by 12Z. Elevated skinny
CAPE (500 j/kg or less) may lead to a few weak thunderstorms here
and there, mainly over south central SD. With the synoptic pattern
mentioned above, models indicate this large area of rain will be
very slow moving/near stationary at times over central SD as storm
motion of only 10-15kts is forecast, per HREF. Precip looks to taper
off northwest to southeast Sunday night as dry air moves in aloft
behind it with a high. With this ongoing high to our northeast and
easterly winds, this will bring in drier air with a sharp cutoff on
where rain is falling and where it`s just sprinkles or dry over
NESD. As of now, this lies along and east of a line from Hecla to
Milbank where pops will be under 20% or less with pops increasing to
near 100% further southwest you go in the CWA. EC ABR/ATY model
soundings shows this drier air below 700mb leading to higher
confidence on less rainfall amounts here. Any shift in this high or
shift in the wave aloft will greatly influence where this sharp
cutoff in pops and QPF lie, so lower confidence on this, with high
confidence on the highest pops/QPF over south central SD and lowest
over western MN.

QPF ranges from nothing to a few hundredths over far northeastern
SD/MN with the potential of 1 to 2+" over south central SD per both
HREF and NBM. Deterministic models are more bullish on this higher
precip potential over south central SD ranging from 3-4" per
GFS/Canadian as well as ARV/FV3. EC/NAM are on the lower end of 1-
2". 90th percentile of both HREF/NBM does show this higher end
potential. Especially if the system ends up slowing down or
really stalling over the area. So therefore as of now, the
probability of exceeding 1" of rainfall or more is 75-90% along
and south of a line from Eagle Butte to Highmore with a 40-60%
chance of 2" or more of rainfall for this area. Potential
rainfall amounts drop off dramatically with little if any
expected east of a line from Aberdeen to Watertown. NBM 25-75th
QPF spread is still on the order of an inch or more over central
SD due to uncertainty (and lower confidence) in exact amounts
with less of a spread further northeast in the CWA due to less
overall rain potential. The WPC has put a Slight Risk (15%) of
exceeding flash flood criteria over central SD due to the slow
storm motion combining with PWATs of 1 to 1.4", west of James
River and highest west of the Mo River (above 90th percentile).
No flood headlines issued due to dry soils out here but will
watch for the potential of areal flooding if we do see this
occurring or we get this higher end rainfall.

Behind this system, a clipper will track northwest to southeast over
the Northern Plains Monday afternoon through Tuesday afternoon
bringing the return of showers (and weak thunderstorms) ahead and
along the front as it tracks across the CWA with additional wrap
around moisture continuing over NESD/MN Tuesday afternoon.
Probability of rainfall>0.25" is 50 to 80% over north central
through NESD/MN with the highest chances over Roberts through
Traverse Counties. Again, weak instability of lack of shear will
keep storms from reaching severe criteria. A ridge that will be over
the western CONUS will track eastward and over the central CONUS for
the end of the week. Weak embedded shortwave energy may bring
additional chances of showers and thunderstorms Thursday over far
south central SD and more widespread Friday. Low confidence this far
out on exact setup with general pops of 20-40%. Additional chances
of precip continue through next weekend as -PNA pattern sets up
synoptically and southwest flow aloft over the CWA. Ongoing cooler
air aloft will result in temps being 5-10 degrees below average
Monday through Thursday of next week and near to a bit below average
Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 631 PM CDT Sat Jun 20 2026

Terminals KABR,KATY,KPIR,KMBG

CIGs will be gradually lowering through the TAF period as areal
coverage of precipitation is expected to increase tonight,
especially over KPIR/KMBG. Went with prevailing precipitation at
these sites, while sticking with PROB30 across KABR/KATY where
precip chances are less tonight through Sunday. MVFR VSBY is
possible in areas of SHRA, with perhaps even IFR if heavier TSRA
materialize. CIGs are forecast to reach MVFR, perhaps IFR at
KPIR late tonight into Sunday morning.

&&

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

&&

$$

UPDATE...TMT
DISCUSSION...MMM
AVIATION...TMT