588
FXUS63 KABR 171157 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
657 AM CDT Tue Sep 17 2024

.KEY MESSAGES...

- A Marginal Risk of severe weather (level 1 of 5) has been
  highlighted along and west of the Missouri River this evening.
  The main threats will be strong wind gusts and isolated large
  hail.

- Warm temperatures will continue through Thursday before cooler
  air returns late in the week.

- More seasonal temperatures for mid-week though the weekend.

- Showers and storms through the weekend (20-40% chance for
  moisture).

&&

.UPDATE...
Issued at 645 AM CDT Tue Sep 17 2024

The aviation discussion has been updated below for the 12Z TAFS.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY AFTERNOON/...
Issued at 452 AM CDT Tue Sep 17 2024

Main forecast challenges will be precipitation chances and
associated severe weather potential tonight into Wednesday as a
storm system organizes and shifts into the Northern High Plains and
portions of the western Dakotas.

Early this morning, the forecast area remains mainly quiet weather-
wise, although there`s been a few showers and sub-severe storms
working through far eastern zones in northeast SD and west central
MN. This activity will clear our forecast area by the 5AM hour.
We`ll be left with mainly dry conditions during the daytime hours as
temperature readings warm well above normal again. Highs this
afternoon will top out in the 80s with a few low 90s along and west
of the Missouri Valley. Pressure falls ahead of an upper level low
across the Great Basin will lead to strengthening sfc low pressure
across eastern WY/MT and western ND/SD. A tightening gradient will
lend to an increase in southerly winds with gusts reaching 25-35 mph
during the day.

These winds look to persist into tonight as the aforementioned upper
low shifts into the Rockies and Northern High Plains and a
strengthening low level jet on the order of about 50+ kts develops.
Scattered thunderstorm development is expected across the High
Plains this afternoon. Guidance progs this activity to shift
northeastward tonight into central South Dakota. Instability locally
looks to be modest but limited with moderate deep layer shear. Hi-
res guidance and CAM solutions do paint a picture of somewhat rather
robust convection working into our West River zones this evening
into the early overnight hours. SPC currently highlights our
Missouri Valley zones with a Marginal Risk for severe weather. The
main threats with any storms will be damaging winds and isolated
large hail.

Some of this activity will wane in intensity as it shifts eastward
into the remainder of the forecast area overnight through Wednesday
morning. Although, wouldn`t be surprised if some is longer lived as
it shifts eastward into the James Valley and points east as that low
level jet persists. PoPs will continue in our eastern zones during
the day Wednesday, as a sfc warm front shifts across the eastern
Dakotas and western MN followed quickly by a cold front. SPC
currently highlights northeast SD and west central MN for a Marginal
Risk for severe weather on Wednesday. Not surprising given the more
favorable instability and deep layer shear that`s progged to be in
place Wednesday afternoon. Much drier air will move into central SD
Wednesday afternoon with dew points dropping into the 40s. This in
combination with gusty southwesterly winds will lead to elevated
fire weather concerns as relative humidity values fall to around 20-
25 percent West River.

&&

.LONG TERM /WEDNESDAY EVENING THROUGH MONDAY/...
Issued at 452 AM CDT Tue Sep 17 2024

The upper pattern through the long term evolves from a longwave
trough over the western CONUS, and departing upper low/wave in
eastern Montana/western ND to a more zonal/progressive flow late
Wednesday/Thursday. There will be a cutoff low across the 4-corners
region that will eventually re-integrate into the flow over the
region for the weekend resulting in the development of a weak
longwave trough across the central CONUS. There is recent better
consistency between the long range deterministic members,
particularly the GFS/EC... with the Canadian is a little stronger
with the longwave trough that develops late in the period, with the
12Z cluster analysis suggesting a much greater spread in ensemble
solutions than what would be inferred from the current 500mb
analysis...raising confidence in the overall forecast.

At the surface, the departing wave and wrapped up low over eastern
MT/western ND will support a cold front looping down into western
South Dakota. There will also be the remnants of a trough washed out
in eastern South Dakota which by this point is mainly just
convergence in the low level winds. This will support continued
convection from earlier in the day, under a high shear low CAPE
environment. The other issue of concern is the strong southwest flow
behind this boundary, particularly across the Missouri valley, which
will enhance mixing leading to warm, dry and windy conditions.
Thankfully much of the area has seen recent rainfall and much of
this is happening during the evening/overnight...so fire weather is
less of a concern.

Cold frontal passage and zonal flow aloft means much milder/more
seasonal temperatures through the extended. NBM 25th/75th percentile
temperatures trend towards increased range as a weak system
Friday/Saturday supports a surge of warm advection followed by a
cold front. It remains around +/- 8F for the weekend into next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 645 AM CDT Tue Sep 17 2024

Terminals KABR,KATY,KPIR,KMBG

All 4 terminals will continue to experience VFR conditions through
the next 24 hour forecast period. Southerly winds will gust up to
30 kts from late morning through tonight. Strong winds just off
the surface will allow for the potential for low level wind shear
to develop at KABR/KATY/KPIR terminals late tonight into early
Wednesday. Showers and thunderstorms are expected to develop west
of the area this afternoon and make their way toward KPIR/KMBG
area by mid to late evening.

&&

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

$$

UPDATE...Vipond
SHORT TERM...Vipond
LONG TERM...Connelly
AVIATION...Vipond