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831
FXUS63 KABR 201929
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
229 PM CDT Fri Sep 20 2024

.KEY MESSAGES...

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- Low probability chance (20-30%) of showers and thunderstorms
  tonight mainly east of the James River valley.

- Strong cold frontal passage tonight into Saturday morning
  creating cooler and windy conditions for Saturday. Peak wind
  gusts behind the frontal passage tonight between 35 and 45 mph
  over areas west of the James River Valley.

- Near normal to slightly below normal temperatures Sunday into
  early next week. Above normal temperatures return Wednesday and stay
  around for the rest of the week.
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&&

.SHORT TERM /THIS EVENING THROUGH SATURDAY NIGHT/...
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Issued at 225 PM CDT Fri Sep 20 2024

At 2pm CDT, skies are sunny and temperatures are warming through the
70s and 80s. Winds have picked up a southerly component today and
are ranging generally from 5 to 15 mph.

There will be cold frontal passage tonight over the CWA. Prior to
the front reaching the I-29 corridor in northeast South Dakota, a
southerly low level jet is forecast to develop over the region with
the nose/focus over northeast South Dakota between ~03z and 06z
before the focus area moves into Minnesota after 06Z. If there were
higher CAPE/instability progs showing up tonight over that area
where the nose of the low level jet is supposed to set up late this
evening, the forecast would be calling for elevated supercells and
large hail potential, because many other parameters for severe
storms are all showing up as favorable. But, with
moisture/instability/CAPE expected to be lacking, the likelihood of
storms developing is rather low.

The front, itself, has characteristics in the model data of being a
rather strong/sharp frontal passage with an abrupt change from east
or southeast to northwesterly for wind direction. The 3-hourly
pressure tendency progged in the NAM/GFS is on the order of 5 to
7hpa. But, because this frontal passage is occurring at night, it
may be tough to translate the stronger post-frontal winds aloft all
the way down to the surface. Covering strong wind gusts potential
late tonight with a special weather statement over counties west of
the James River valley.

The rest of the short term could be described as a prolonged period
of low level CAA and surface high pressure influence, as a Canada-
sourced high builds down across the region.
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&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
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Issued at 225 PM CDT Fri Sep 20 2024

As an upper-level low pressure trough moves northeast Sunday over
Manitoba, a ridge located over the Pacific coast will also start
moving east. By Tuesday morning, the jet streak on the eastern side
of the ridge moves over western SD, creating more northerly flow
over the state. The mid-levels stay relatively dry over SD, only
moving in some moisture Tuesday morning. Cold air is advecting
through the mid-levels Sunday morning over central and eastern SD
and moves out by Monday morning. Behind that, more CAA occurs Monday
evening until Tuesday. With the upper-level ridge moving east
affecting the flow at the surface, Tuesday will see a cold front
move across SD. Though this front provides the lift needed to
develop precipitation, the forcings and moisture are not there to
develop anything. The likelihood for precipitation Sunday through
Tuesday is low. With the CAA occurring in the mid-levels, the
temperatures at the surface will decrease. Sunday`s temperatures
will be slightly below normal, then temperatures will increase
slightly Monday and Tuesday, to be around normal for this time of
the year. Tuesday will see cooler temperatures than Monday in
areas west of the Missouri River because of the cold front moving
through.

After Tuesday evening, models show the upper-level ridge continuing
to work its way east over SD. However, there is some variability in
the clusters and deterministic models in the strength and how far to
the north the ridge pushes after that. Depending on these
differences, the upper-level flow varies between coming from the
northeast, north, or northwest. The contrast in upper-level flow
causes slight differences in mid-level temperature advection as a
majority of models show WAA over SD for the rest of the forecast
period, but the GFS has CAA over eastern SD until Thursday
afternoon. The mid-levels look to stay relatively dry in the models
until Friday morning when the ECMWF and GFS move moist air over
eastern SD. This moisture doesn`t help with the development of
precipitation from Wednesday to Friday, as precipitation stays out
of SD. The WAA in the mid-levels associated with the ridge help to
warm temperatures at the surface after Wednesday morning. This will
cause temperatures to be above normal for this time of the year, by
5 to 15 degrees. While central and eastern SD had a taste of fall
temperature earlier in the forecast, it will still be a bit before
it feels like autumn again.
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&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1236 PM CDT Fri Sep 20 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail across the area this afternoon through
Saturday morning. Low-level wind shear is forecast to develop
over the KATY region overnight.

&&

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

$$

SHORT TERM...Dorn
LONG TERM...Vernon
AVIATION...Dorn