Amherst, South Dakota Weather Forecast Discussion

946
FXUS63 KABR 040815
AFDABR
Area Forecast Discussion
National Weather Service Aberdeen SD
315 AM CDT Sat Oct 4 2025
.KEY MESSAGES...
- Near record high temperatures will remain possible east of a
  line from Pierre to Ipswich today, where highs will be in the
  mid 80s to near 90 degrees.
- Windy conditions today and tonight will be east of a line from
  Presho to Aberdeen, where winds out of the south will gust 30 to
  40 mph. On Sunday the winds will be switching out of the
  northwest, with gusts of 35 to 45 mph with locally higher gusts
  possible.
- There is a marginal risk, level 1 out of 5, for isolated severe
  storms this evening and tonight along and west of a line from
  Britton to Chamberlain. Damaging winds will be the main concern.
  Heavy rain or hail will also be possible.
- There is a 50 to 75% chance of rain in excess of 1" along and
  west of a line from Pollock to Eagle Butte tonight through
  Sunday morning.
- Localized frost is possible Monday morning, Tuesday morning,
  and Wednesday morning, mainly over portions of northern SD.
&&
.SHORT TERM /TODAY THROUGH SUNDAY AFTERNOON/...
Issued at 312 AM CDT Sat Oct 4 2025
As of 3am, temperatures are balmy, ranging in the upper 60s to the
lower 70s with dewpoints in the upper 50s to the lower 60s. Winds
are out of the south gusting between 20-35 mph over the CWA with
satellite indicating high clouds moving northeast over northeastern
SD/western MN with the rest of the CWA clear. The main highlights
for the short term will be the ongoing windy conditions across the
forecast area through the weekend and the threat for isolated severe
storms this evening/tonight, mainly over central SD.
The low level jet that was positioned over the area overnight will
shift eastward and over the James River Valley into MN by 12Z. With
southerly winds at the surface and this LLJ, downsloping winds off
the Coteau will continue (with gusts up 40mph) before diminishing by
mid morning as the LLJ weakens a bit. Otherwise, this elongated area
of low pressure stretches from southeastern Manitoba and
southwestward through southwest SD with the northeast to southwest
oriented cold front hovering over north central SD by 12Z. This cold
front will slowly shift eastward across the CWA today (and its low
attached to it) with the front only halfway across SD by 00Z. By 12Z
Sunday, the western 2/3rds of the state will be behind the fropa
with far eastern SD ahead of it. Another faster moving cold front
will pass northwest to southeast over the CWA Sunday, catching up
with the first cold front, with the system finally exiting the CWA
by Sunday afternoon with the entire CWA in north to northwest flow.
With ongoing steep pressure gradients today (and the low directly
over the CWA) along with daytime mixing (mixing levels ~800-850mb
east of the Missouri River), will lead to another day of windy
conditions ahead of the front. For example KATY sounding indicates
momentum transfer up to 39kts at the top of mixing layer by peak
heating with areas around the northern Coteau up to 25-30kts
(inverted V soundings). HRRR indicates winds highest over east
central SD between 30-40 mph. Again, with being WAA driven, I was
hesitant on going full NBM/NBM90, but did increase it a bit closer
to the HRRR. The LLJ restrengthens tonight, with speeds at 850mb by
06Z ranging from 50-60kts over the James River Valley and eastward.
With this and southerly winds at surface, gusty winds will be likely
over the Coteau with the highest gusts on the eastern side of the
Coteau (downsloping). Gusts are forecasted to range from 35-40kts.
Pressure rises behind the front (2 to 10mb/6hr GFS, highest central
SD by 12Z Sunday and west of the James River 18Z) along with CAA
will increases winds over central SD in the morning and will spread
eastward over the CWA as the higher pressure rises/CAA shifts
eastward behind the front. Due to this, I did incorporate NBM90th
with forecasted wind gusts between 30-40kts over the entire CWA by
Sunday afternoon, highest over the Coteau, and will finally start to
diminish west to east early Sunday evening. With the gusty winds and
drier fuels, collaborated with surrounding offices and issued an SPS
for portions of east central through northeastern SD into west
central MN for elevated fire danger conditions this afternoon.
Most of the precipitation expected with this system looks to be post
frontal with precip really not moving into our far western CWA until
00Z Sunday or so. This precip will spread a bit eastward through 12Z
Sunday with the highest pops of 60-95% along and west of the Mo
River, highest over north central SD. Precip will continue mainly
over our northwestern CWA Sunday morning through the afternoon with
lingering pops of 40-75%, highest over north central SD. Probability
of rainfall>0.50" from 00Z-18Z Sunday is 55-95% over north central
SD, highest over Corson/Dewey. Rainfall>1" is 50-75% for western
Corson/Dewey. However, the spread between the 25th-75th for rainfall
per NBM is quite high along and west of the Mo River, with the
spread ranging from 0.50" up to 1.5", highest over north central SD.
So confidence remains lower on exact totals for this area. There is
also a marginal risk, level 1 out of 5, for isolated severe storms
this evening/tonight along and west of a line from Britton to
Chamberlain. Most of the higher instability will be displaced and
ahead of the cold front with most of the thunderstorm activity being
post frontal as mentioned, therefore, being elevated. MUCape will be
pretty marginal, up to 1300 j/kg or so, however speed shear behind
the front will range between 30-50kts. Depending on how east the
storms go, additional energy could be provided by the LLJ. So main
threat will be wind gusts of 60 mph and quarter size hail along with
heavy rain.
Once again ahead of the cold front (east of the MO River) 850mb
temps run on the order on the 90-99th percentile, ranging from 19 to
22C, highest James River Valley and eastward. So highs will range in
the 80s to the lower 90s east of the Mo River with temps behind the
cold front, over north central SD, only in the 70s. Much cooler for
Sunday in the 50s to the lower 70s, warmest over far eastern
SD/western MN.
&&
.LONG TERM /SUNDAY EVENING THROUGH FRIDAY/...
Issued at 312 AM CDT Sat Oct 4 2025
Really all we have to talk about in the extended is frost potential
and even that continues to diminish in probability with the latest
runs and ensemble guidance. The long term starts Sunday evening. The
wave/low has departed and a broad, cool surface high is coming in
out of Canada. Unfortunately there is a range between deterministic
guidance on the specific placement of the surface high, between
north central South Dakota, northeast South Dakota or back over the
western Dakotas. That means we could see either very favorable
radiational conditions or a persistent mixing wind which will temper
the drop in temperatures. The 25th-75th percentile range in low
temperatures for north central South Dakota runs between near
freezing to upper 30s. That gives us a probability for a frost right
around 50/50 for north central South Dakota (negligible elsewhere).
The surface high moves off, and despite highs only in the mid 50s to
low 60s, deterministic NBM is still forecasting temperatures down
into the upper 30s to low 40s. This is when we would typically
observe widespread ideal radiational conditions, so hard to believe
that temperatures wouldn`t respond more dramatically. NBM 25th
percentiles are pretty widespread mid 30s, though probabilities for
actual below 36 degrees are fairly limited to a smaller area of
north central South Dakota. A backdoor front clips the area early
Tuesday as well, but not so far into the CWA (more like just barely
western Minnesota) so that may lead to a slight enhancement in winds
but doens`t seem like it would be all that a significant feature.
Anyway, on to Wednesday with originally the higher/widespread
probabilities for frost. That has now dropped to only 20-30%. So the
way things are going, frost may be only patchy here and there for
the next few days and then we go back to above normal temperatures
for the latter half of the work week and next weekend.
&&
.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1212 AM CDT Sat Oct 4 2025
Terminals KABR,KATY,KPIR,KMBG
Low-level wind shear will continue to be a concern during the
overnight hours, with 40 to 50 knot south-southwest winds around
2000ft. Southerly surface winds will continue to be gusty through
much of the period for KABR/KATY, but KMBG/KPIR will start to see a
wind shift to the north as a frontal boundary moves east. Some
uncertainty to the exact timing of the wind shift, especially in the
KABR area, which may occur roughly around 00Z Sunday. -SHRA is also
forecast to affect portions of central SD Saturday night, along with
MVFR CIGs arriving right towards the end of the TAF period for KMBG.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
SHORT TERM...MMM
LONG TERM...07
AVIATION...MMM

NWS ABR Office Area Forecast Discussion