320
FXUS63 KABR 140802
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
302 AM CDT Wed Aug 14 2024

.KEY MESSAGES...

- There is a Marginal Risk (level 1 of 5) for the entire area late
  Wednesday afternoon through the early overnight hours. Large hail
  and strong wind gusts are the main threats. Probability for moisture
  is between 30 and 70 percent.

- Showers and weak thunderstorms will wrap back into northeast South
  Dakota and western Minnesota during the day Thursday (30-60%) and
  tapper off Thursday afternoon.

- Temperatures will remain seasonal through early next week.

&&

.SHORT TERM /TODAY THROUGH THURSDAY AFTERNOON/...
Issued at 301 AM CDT Wed Aug 14 2024

The ridge axis continues east with a southwest flow shortwave headed
from western Nebraska into southeast South Dakota while another wave
is located in western North Dakota, while the main shortwave/trough
sits in eastern Wyoming. Thus, we really remain in a gap with only
weak convective elements scattered across the CWA.

As the day progresses, the shortwave to the south could generate
some convection along the CWA border between
Chamberlain/Huron/Brookings but there is low confidence much will
actually make it up to even Watertown, while the convection in North
Dakota develops through the course of the day. The southwards
extension of that shortwave, and wave progressing towards the
western portions of the state will phase enough that there is some
potential for storms to develop in northwest/north central South
Dakota during the afternoon. There should be a very subtle inverted
trough across the area, helping to provide a focus for convection.
The rest of the CWA, between systems, will continue to only see a
low chance for moisture through the afternoon without much forcing
and a weakly unstable atmosphere overhead. The environment during
the afternoon in north central/central South Dakota will have
favorable MUCAPE at around 2k j/kg, but shear is still relatively
weak at 30kts or less. This might just enough for some storm
organization as CAMS generate a cluster/line type system.  High
PWATS and a slow storm motion (hodographs suggesting about 10-20mph)
present a heavy rain risk, though overall storm motion would be
enhanced by the organization into an MCS if CAMS are correct.

The subtle shortwave/trough pivots into south central North Dakota
this evening and then loops down into western Minnesota allowing
convection to migrate eastwards across the northeast of the state
and on into western Minnesota. Severe weather threat should diminish
with only about 1k j/kg MUCAPE and weakening shear. Those who need
moisture will probably benefit from the system lingering across
northeast SD/western MN with showers/wrap around moisture persisting
into the day Thursday.

&&

.LONG TERM /THURSDAY EVENING THROUGH TUESDAY/...
Issued at 301 AM CDT Wed Aug 14 2024

Clusters have a good handle on the synoptic pattern Friday into the
weekend with a ridge building over the central CONUS (and mid level
high underneath) as the shortwave/sfc low continues to push east and
over the Ohio River Valley/Northeast by Sunday. To our west, the low
off the Pacific coast will continue to strengthen. This setup
creates an omega block pattern with not much movement through early
next week. Models indicate this closed low over the Pacific weakens
a bit into an open wave by Tuesday, but there are differences
between the Clusters on exact timing of this. By midweek, ensembles
really diverge on exact location and amplitude of the ridge.

Thursday evening into Friday morning, the occluded low is forecasted
to be positioned over ~MN/WI border, which could bring ongoing
lingering wrap around elevated rain showers/storms over northeastern
SD/western MN. However, the western extent of this precip remains in
question and exacting timing of departure as EC/GEPS is a little
quicker with the exit compared to GEFS. Latest NBM has a 15-20% pops
over far northeastern SD/western MN between 00-06Z Friday with
precip exiting this area before 12Z. Otherwise, a high moves in and
remains dominant over the Northern Plains Friday through the
weekend. A low pressure system looks to move eastward over Canada,
north of this high, during this time. Models indicate several
potential shortwave vorts/pulses moving up the ridge and along the
axis (from the trough out west) along with pockets of mid level
moisture. This could lead to isolated chances of thunderstorms as
the ensembles show spotty chances of precip here and there over the
CWA occasionally through the period, especially with diurnal
heating. There is the possibility of a couple surface boundaries
passing through early to middle parts of next week too. Low
confidence on exactly where precip is possible, due to the isolated
nature at this point. NBM keeps a generalized 15-25% through the
long term period. Cape looks to creep up to 1000-1500 J/kg over
central SD with shear 30-40kts over this area on Saturday. CSU
highlights a 5% chance of severe weather possible.

With the backside of the low, northwest winds continue over the
eastern CWA with southeasterly winds over the western CWA at 850mb
for Friday. Forecasted highs will range in the mid to upper 70s to
the upper 80s, warmest around and west river. As the ridge builds
and southeasterly winds expand eastward, highs through the weekend
will mainly be in the 80s with possible lower 90 readings over south
central SD on Sunday/Monday where the warmer 850mb temps are (~20-
22C), under the ridge. NBM prob of 90 ranges from 30-50% in this
area. Climate Prediction Center indicates prob of above average
temps next week only between 35-45% from the James River Valley and
westward so expect closer to near normal to slightly above temps.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1220 AM CDT Wed Aug 14 2024

Terminals KABR,KATY,KPIR,KMBG

MVFR/IFR CIGs are forecast to overspread the region by morning, with
areas of SHRA/TSRA as well. Areal coverage and placement of
shower/storm clusters are a bit uncertain, but signs point to better
coverage during the afternoon/evening hours. Any heavier downpours
may produce MVFR/IFR VSBY at times if they manage to move over a
TAF site.


&&

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

$$

SHORT TERM...Connelly
LONG TERM...MMM
AVIATION...Connelly