Watertown, South Dakota 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

162
FXUS63 KABR 271146 AAB
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
646 AM CDT Fri Jun 27 2025

.KEY MESSAGES...

- Areas of dense fog across central South Dakota during the
  morning hours may bring down visibility as low as one-quarter
  mile at times.

- The entire forecast area has been classified as SLIGHT RISK (2
  of 5) for severe weather this afternoon/evening. Large hail (2-
  3")/Winds (60-80mph) are the main threats, however we also have
  the potential for tornadoes mainly between the Missouri and
  James Rivers.

- SLIGHT RISK (2 of 5) again for Saturday, mainly east of a line
  from Aberdeen to Pierre, with a large hail and wind threat.

&&

.UPDATE...
Issued at 639 AM CDT Fri Jun 27 2025

Aviation discussion updated below for the 12Z TAFs.

UPDATE Issued at 525 AM CDT Fri Jun 27 2025

Just a quick update to cover the placement of and intensity of fog
outside the originally forecast area. Dense fog advisory has been
issued through 9am.

&&

.DISCUSSION...
Issued at 235 AM CDT Fri Jun 27 2025

Stratus and some fog are already in place across the CWA, but for
how long? Low level flow transitions from northeasterly to south-
southeasterly, a trajectory from which the stratus cu-off now
resides. Looking at the 00Z ABR RAOB its noted that the cloud
thickness is only about 1.5kft, so if we get any breaks they would
erode quickly.  Thus, the premise that CAMS should dissipate stratus
rather quickly this morning with some pretty big jumps between 16-
18Z to the northeast in the HREF seems adequate and the expectation
is that stratus will not play a significant part in the hindrance
of the later day severe weather threat.

500mb flow this afternoon is marked by a departing shallow mid-level
ridge and a western CONUS/Rockies shallow trough. Embedded within
this flow is a very subtle wave over western North Dakota tailing
down into northwest South Dakota, and while its subtle at least
aloft is primarily neutral flow aloft. As for the storm environment,
shear in the mid/upper levels is mainly unidirectional at 20 to
45kts, with light low level southeasterlies around convective
initiation. 0-6km shear is about 50kts with a core in central/north
central SD of 0-1km SRH thats running up to about 100m2/s2 this
afternoon/evening... however a transition will occur with loss of
daytime heating, and 0-1km SRH will be on the increase overnight as
1/2km winds increase to 45-50kts by 06Z, up to around 200m2/s2. HREF
probability of CAPE in excess of 3500j/kg is 60-70% so plenty of
instability. So what`s the MO for convection later today? Shear
profiles suggest supercell characteristics, with strong RFD thanks
to westerly mid-level flow and dry air at 10kft. Tornado potential
isn`t anything to write home about with the low 0-1km shear, but a
transition in the evening with that low level jet means there is a
window in which discrete storms would have a tornado potential
before becoming elevated. High CAPE and shear also presents us with
a large hail threat.

As for timing/locations, the Missouri valley will be the focus
primarily this afternoon/evening. A lee low sets up in Wyoming, with
broad southeasterly low level flow presenting a slight upslope
across the state. The lack of low level focus and generalistic upper
level support means confidence on timing/location is generally low,
though CAMS support plenty of evidence that storms will develop and
move across the Dakotas this afternoon/evening. Storms continue
east into the early morning thanks to the low level jet, although
weak upper level support again means low confidence on
coverage/timing.

Saturday, shear remains strong at about 40kts in the HREF. CAPE is
also again up around 4000j/kg. So the main question is where has the
lee low/inverted trough stalled as the focus for convection to
develop? We also have the issue of the flow aloft only being weakly
diffluent and relying on another weak/subtle shortwave to provide the
upper level support. Focus remains as per previous forecasts across
far eastern South Dakota/western Minnesota.

A more pronounced trough moves through Sunday with early frontal
passage. This is followed by a weak, shallow and slow moving high
pressure system so later half of Sunday through into early Tuesday
should be dry. That is followed by some ridging with northwest flow
aloft for mid-week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 639 AM CDT Fri Jun 27 2025

Terminals KABR,KATY,KPIR,KMBG

Widespread IFR CIGs across the region this morning will slowly
erode from west to east through the day, while perhaps improving
to MVFR as this happens. Areas of FG/BR are also affecting parts
of the region, especially central SD where VSBY has been down to
IFR as well, even below 1SM at times.

After the fog and low clouds become less of an issue by this
afternoon, focus then shifts to TSRA/+TSRA potential across much
of the region. Areal coverage may be somewhat limited, so used
PROB30 to handle this. Severe storms are possible though, and if
one were to move over a TAF site, strong surface wind gusts over
50 knots are possible, along with large hail (GR) and IFR VSBY.
Timing for this is somewhat uncertain, so low confidence timing
within PROB30 groups, unfortunately. Looking at the evening hours
mostly.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 10 AM CDT /9 AM MDT/ this morning for
     SDZ003>005-009-010-015>017-033>037-045-048-051.

MN...None.
&&

$$

UPDATE...TMT
DISCUSSION...07
AVIATION...TMT