423
FXUS63 KABR 301754 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1254 PM CDT Tue Apr 30 2024

.KEY MESSAGES...

- Scattered light showers this morning.

- Thunderstorms developing in the afternoon mainly east river. For
  far northeastern SD/western MN, cant rule out a storm or two with
  one inch hail or greater and/or winds in excess of 60mph from about
  noon through about 5pm.

- Active pattern continues with at least 3 or 4 notable waves
  moving through the region providing rainfall chances. Thunderstorm
  chances (including potential for severe storms) overall, look rather
  low through the period.

- Near to below normal temperatures early in the period potentially
  warming to near or above normal beginning Sunday into early next
  week.

&&

.UPDATE...
Issued at 1242 PM CDT Tue Apr 30 2024

Aviation discussion updated below for the 18Z TAFs.

UPDATE Issued at 1013 AM CDT Tue Apr 30 2024

Made a few minor adjustments to the forecast grids this morning to
bring them more in line with the observed trends, otherwise things
remain on a decent track. Showers and a few scattered
thunderstorms will continue to shift east-northeast across our
forecast area through this afternoon. A couple of stronger storms
will be possible in our far southeast zones during the afternoon
hours. We`ll try and make a run at the low to mid 60s for highs
this afternoon, but if cloud cover remains extensive and given the
rainfall, we may fall a bit short.

UPDATE Issued at 621 AM CDT Tue Apr 30 2024

Aviation discussion updated below for the 12Z TAFs.

&&

.SHORT TERM /TODAY THROUGH WEDNESDAY AFTERNOON/...
Issued at 333 AM CDT Tue Apr 30 2024

Mild level warm advection responsible for some very small convective
cells which are increasing in coverage from Mobridge to Faulkton at
2am...pushing steadily east-northeast. Mild level cloud deck is more
expansive in central/eastern SD, and while it will have an impact on
temperature forecast (cooler through the morning hours), it won`t
have quite the impact on heating as the last several days.

Compact, negatively tilted shortwave will dominate the weather for
today, with about 50kts of flow at 500mb out of the southwest, and a
90kt jet streak nosing up into southeast South Dakota. BUFKIT
profiles for KATY show rapidly steepening mid level lapse rates
before frontal passage followed by a cooling profile with skinny
CAPE in a high shear environment thanks to the aforementioned strong
mid-level flow. CAM ensembles 25th/75th CAPE values range from a few
dozen to upwards of 700j/kg and a 25th/75th range in 0-6km shear of
about 50kts to around 60kts. Granted, we are on the very northern
extent of this plume of instability, CAMS do initiate surface based
convection in the far eastern CWA before it moves into western
Minnesota. Overall QPF should be limited by rapid speed of
convection along with the short interval in which it is in the CWA.

Winds on the backside continue to slide, with the CAM ensembles
25th/75th percentiles running between low 20s to about 30mph. That
is a little lower than the NAM/GFS BUFKIT mixed winds which top out
around 30-35kts, but fall well short of NBM and its near advisory
level winds for our more wind prone areas.

The period of dry weather extends overnight before flow aloft
becomes southwesterly. Mid level warm advection within this regime
will support shower development lifting from Nebraska into
central/eastern South Dakota during the day Wednesday.

&&

.LONG TERM /WEDNESDAY EVENING THROUGH MONDAY/...
Issued at 333 AM CDT Tue Apr 30 2024

Pattern looks to remain rather active in the extended period, with
multiple shortwaves moving across the Northern Plains, bringing
periods of rainfall chances. First shortwave kicks off right away as
models show energy crossing the region Wednesday night through
Thursday. Highest probabilities for >0.25in rainfall (24-hr period
ending at 00Z Friday) amongst the GEFS/GEPS/ENS are well southeast
of the region, but percentages within the CWA generally fall between
30% and 50% on the Grand Ensemble. ENS is the lowest, ranging from
about 15% to 50%, while the GEPS is the highest from 40% to 80%.
Highest inherited PoPs from the NBM range from about 50% to 70%
across the CWA Wednesday night through Thursday.

Friday night into Saturday provides another opportunity for
organized precipitation. Probabilities for >0.25in (24-hr period
ending at 18Z Saturday are considerably lower than this first wave
mentioned above, generally around 40% or below amongst the
GEFS/GEPS/ENS. And yet, more shortwave energy potentially for Sunday
into Monday.

As for thunderstorm chances (including severe storm potential) with
these waves, a look at probability for surface CAPE >500 J/KG,
surface CIN >-25 J/KG, and 0-500mb bulk shear >30 kts show little to
no chances of occurrence through the entire extended period. So,
don`t really see anything too convincing for organized strong to
severe storm potential at this time with these 3 or so waves moving
through during the extended period, or even general thunder in any
sort of organized/noteworthy coverage.

As for temperatures, generally 50s and 60s for highs during the
first half of the extended, with signs of warming towards the end of
the period (beginning Sunday) as highs rebound into the 60s and 70s.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1242 PM CDT Tue Apr 30 2024

Terminals KABR,KATY,KPIR,KMBG

Rain showers with embedded thunderstorms will continue to push
across portions of northeast South Dakota through the afternoon
affecting the KABR and KATY terminals. Occasional lighter showers
will be possible at KPIR and KMBG through the afternoon. KATY will
have the best chance to see a few -TSRA/TSRA with tempo vsby
reductions to MVFR. Lower cigs will be possible through the
majority of the afternoon hours at KABR and KATY before improving
to VFR this evening. Gusty west to northwest winds between 25-35
kts will be possible at KPIR and KMBG through the afternoon into
the evening before relaxing by mid to late evening.

&&

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

$$

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