Sisseton, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

248
FXUS63 KABR 191126 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
626 AM CDT Sat Jul 19 2025

.KEY MESSAGES...

- There is a marginal risk, level 1 of 5, for severe storms
through Monday, with hail of 1 inch in diameter and winds of 60
miles per hour the main threats. The areas of concern are along and
west of the Missouri River this evening, then over much of the area
both Sunday and Monday, primarily during the afternoon and night.

- Heat index values will be in the upper 90s to near 100 degrees
Monday afternoon, across central SD primarily south of Pierre.

&&

.UPDATE...
Issued at 621 AM CDT Sat Jul 19 2025

Updated for 12Z Aviation Discussion below.

&&

.DISCUSSION...
Issued at 327 AM CDT Sat Jul 19 2025

High pressure in northeastern ND and northwest MN has been having an
influence on the area behind the surface trough that has slid
southeast of the area. This is allowing slightly drier air into the
area and a little better mixing on the northerly low level flow.
That has led to a north to south improvement of the fog that has
been over east central SD and stretching southwest through Huron and
into Buffalo county. Expect that to continue through daybreak, so
have shown that trend in the forecast grids. Otherwise, have a
variety of clouds over the region, with low stratus moving in under
the northerly flow (trending down from VFR towards MVFR/IFR over the
last few hours), then high clouds drifting east from the showers
exiting WY and moving into western ND. Both of these areas of clouds
will continue to influence the area heading into the daytime hours
today.

Clouds are tricky today, as model soundings show the stratus
moisture being fairly shallow and largely trapped below the 900-
850mb inversion. So the question is how quickly we`ll be able to mix
some of that moisture out with the inversion in place. Models are
fairly consistent on trying to have that occur through the mid day
and afternoon hours (especially over the north), but did hold onto
at least partly cloudy skies along/south of US-212 with the
uncertainty on how well that mixing will impact areas well into the
stratus. Plus, CAMs/HREF have that area seeing mid-high clouds
downstream of potential showers moving into and diminishing in parts
of central SD. Those showers, currently near the WY/SD border, will
continue to track east this morning and move into central SD to the
south of Mobridge. There`s abundant dry air between 850-600mb, so do
have concerns there may not be too much that makes it to the surface
and that will also help diminish the showers as they try to move
east of the MO River. Thus, have kept PoPs in the slight/chance
category for today.

Later in the day, convective development will occur to the west of
our area and towards the SD/WY/MT/ND border areas. Expect storms to
develop during the late afternoon and early evening in the area of
better instability (1-1.5k MUCAPE axis). Those storms will move to
the east-southeast with time, but also move out of the better
instability as they approach the area. So will continue to mention
some low end chances for the west river area this evening, but think
the severe threat should diminish as they approach our CWA during
the late evening hours. They may hold together as they push east,
but confidence remains low on how far they make it, so limited the
chance PoPs to the areas west of the James River during the
overnight hours.

Sunday and Sunday night continue the potential for thunderstorms, as
a low will be positioned over WY. There may be a surface trough
setup over southwest SD, with dry line stretching south into western
NE. That could lead to a little bit of a focus for storm development
in the afternoon over central SD (KPIR area), as CIN diminishes by
mid afternoon and MLCAPE values increase to 1.5-2.5k J/kg. But the
more consistent signal is for storms to develop in western ND and
potentially into north central SD during the late afternoon and
evening hours. Continued to highlight those chances in the PoPs, but
also may need to watch for storms in ND dropping southeast into our
northern CWA in the afternoon (a lower probability solution and only
shown by a couple CAMs). Where the convection develops, severe
storms are possible with the previously mentioned instability and
ample shear under the persistent/strong west-southwest flow aloft.
The storms would move to the east with time on Sunday night and thus
chance to likely PoPs follow suit in the forecast.

For next week, the larger scale pattern has the previously mentioned
upper trough over the PacNW through at least mid week, as the upper
ridge remains over the Great Lakes and Ohio River valley region.
That should provide enough ridging over at least our southern areas
to allow temps to rise above normal over south central SD and also
brings heat concerns as apparent temperatures rise into the upper
90s to near 100 on Monday and potentially Tuesday. In addition,
expect periods of shortwaves to eject out from the upper trough to
the west and slide across the northern Plains. This will bring
continued opportunities for showers/thunderstorms, as there should
be ample instability through that time. With strong w-sw flow aloft
at 500mb continuing, ample shear remains and a severe threat is also
in place. That shows up in the ML products, with elevated
probabilities over the northern Plains through at least Tuesday,
before a surface trough or weak cold front slides just far enough
south to allow high pressure to build over the Dakotas and keep
probabilities highest to the south of the area. That will bring a
slight reduction of temps for mid week, before they increase again
heading into next weekend as the upper ridge focuses farther to the
west and over the central CONUS.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 621 AM CDT Sat Jul 19 2025

Terminals KABR,KATY,KPIR,KMBG

Low stratus will continue to influence KABR/KATY this morning, but
do have low confidence on the exact timing of the departure as the
low level moisture gradually mixes out today. Think KATY will see
a brief break over the next couple hours before going back into
the stratus again. Have both departing the low stratus around mid
day based on latest models and shallow nature of the moisture,
but with upstream stratus extending a good ways northeast, that
may be a tough optimistic.

Otherwise, the focus for the rest of the period is the potential
for some light showers and maybe a rumble of thunder around mid
day at KPIR, then watching expected thunderstorm development
upstream near the ND/MT/WY/SD border and then moving to the east-
southeast this evening. Think KMBG/KPIR have the best chance of
seeing some showers/thunderstorms, so included a PROB30 for that.

&&

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

$$

UPDATE...SRF
DISCUSSION...SRF
AVIATION...SRF