259
FXUS63 KABR 232348 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
648 PM CDT Thu May 23 2024

.KEY MESSAGES...

- A slight risk for severe storms (2 out of 5) this afternoon and
  evening. Threats include damaging wind (~60-70 mph), large hail
  (up around the size of golfballs) as well as a tornado or two.

- Showers and weak storms continue into Friday (30-70%) with rain
  chances diminishing southwest to northeast Friday morning. The
  unsettled weather pattern continues with additional chances of
  showers and thunderstorms Saturday into Monday (30-50%).

&&

.UPDATE...
Issued at 640 PM CDT Thu May 23 2024

Aviation discussion updated below for the 00Z TAFs.

&&

.SHORT TERM /THIS EVENING THROUGH FRIDAY NIGHT/...
Issued at 226 PM CDT Thu May 23 2024

A boundary has set up just east of Aberdeen this afternoon with
southerly sfc flow drawing additional moisture and westerly flow
aloft. This boundary is producing enough shear to set off a few
supercells. The question is how much this early afternoon activity
inhibits severe convection later today across the east. Current
thinking is that supercells will begin to develop after 21z between
the Missouri River and James valley, then transition to more of a
linear mode as they reach the James Valley and move east after 0z.
Given the low level shear early on (40 to 50 kts) and the expected
supercell structure, all threats are in play. Instability weakens
east of the James this evening, so more difficult to know how well
the line will hold together to produce severe parameters. Thinking
storms will weaken as they move east toward the Coteau.

The spot to really watch will be a narrow east-west corridor in the
sfc low from Corson through McPherson counties this evening. This
corridor maintains 800 to 3000 J/kg of CAPE as 80 kts of shear moves
in with the jet streak between 0z and 4z. SPC Mesoanalysis page
stretches +1 or better sigtor potential as far east as northern
Brown county.

Cold air advects in tonight with the upper low. Northwest winds with
gusts to 40 to 45 mph are possible, though clouds may limit mixing
somewhat. Well below normal temperatures (by 10 to 15 degrees) are
forecast for Friday with highs in the 60s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 226 PM CDT Thu May 23 2024

Saturday morning, the Friday low has moved off towards the
northeast, but some shortwave energy lingers over the region
bringing some slight rain chances. A shortwave trough moves across
the area Sunday increasing our rain chances and then strengthens
into a low just to our east (over IA/MN/WI) on Monday, trailing
shortwave energy back through our area and up to the north. Tuesday,
that low continues to move off to the east and we move into an upper
level ridge pattern for the remainder of the period.

Sunday, deterministic models mostly keep the rain in central SD,
mainly south of Hwy 12 and west of Hwy 281. The GFS and EC bring
some showers to areas around and east of the James River Monday
afternoon and evening. At this time, the environment does not look
to support storms.

Recent model runs have removed the chance of below freezing
temperatures Saturday morning. As for highs during the period.
Saturday through Monday is expected to be below average, but once
the ridge moves in Tuesday, temps will rise back up to around
normal. Winds look to remain around normal for the entire period.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 640 PM CDT Thu May 23 2024

Terminals KABR,KATY,KPIR,KMBG

SHRA, with TSRA/+TSRA will continue across the region through the
first part of the TAF period. Any stronger cells that affect a TAF
site will be capable of producing hail (GR) and strong surface
wind gusts over 50 knots. MVFR/IFR VSBY possible as well in
heavier cells, along with MVFR CIGs. Areas of MVFR CIGs can be
expected on Friday also.

&&

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

$$

UPDATE...TMT
SHORT TERM...Wise
LONG TERM...KK
AVIATION...TMT