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000
FXUS63 KABR 250903
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
403 AM CDT Thu Apr 25 2024

.KEY MESSAGES...

- Sustained south-southeast winds around 30 mph today, as well as
gusts between 35 to near 45 mph are expected, strongest over north
central SD, and throughout and east of the James River valley.

- A low probability risk of a strong storm or two may present across
north central (generally west river forecast zones) South Dakota by
early evening, with primarily a wind threat (small hail possible,
too).

- Two systems back to back will bring wetting rain to the forecast
area. The first system moves in this afternoon through Saturday. The
second system arrives Sunday, lasting through Sunday night.

- Probability of 48 hour rainfall totals, ending Saturday evening,
ranges from 60 to 95%, highest over the James River Valley and
eastward. Additional rainfall expected Sunday.

&&

.SHORT TERM /TODAY THROUGH FRIDAY AFTERNOON/...
Issued at 403 AM CDT Thu Apr 25 2024

At 3 AM CDT, skies are generally clear across the western half of
forecast zones, while accas and convective debris cirrus cover a
good portion of the eastern half of forecast zones. Temperatures on
southeast winds of 10 to 20 mph have only fallen into the upper 40s
to low 50s. Return flow low level moisture is also evident with
dewpoints running anywhere from 5 to 15 degrees higher than this
time yesterday. A line of elevated showers and embedded thunder,
that developed a few hours ago, continues to work east early this
morning, toward the South Dakota/Minnesota border.

The synoptic set-up for today/tonight showcases the potential for
strong sustained south-southeast winds around 30 mph, with some
higher gusts expected throughout the day and into tonight. Within
this strong return flow wind pattern, the advection of Gulf of
Mexico moisture (seen this morning surging northward through Kansas
and the Colorado high plains) up into South Dakota will be possible.
UNR`s CWA will have the best low level forcing (north-south oriented
lee-of-the-Rockies and Black Hills surface trofs) for convection
routed in the BL today/this afternoon. Storm motion by late this
afternoon/early this evening would take any storms moving with the
mean wind northeastward, potentially toward Corson/Dewey counties.
Deep layer shear would support generally multi-cellular to perhaps
marginally supercellular storm-mode, with generally 500-1000J/kg
MLCAPE to work with. 0-1km and 0-3km SRH are not overly impressive,
but given that convection would be moving into a strongly mixed BL
of southeasterly winds by late this afternoon/early this evening,
perhaps some loosely organized wind-threat may be possible, if
storms line out or build into efficient cold-pool generating
clusters. Saw some of the 00Z hi-res CAM guidance inferring bowing
signatures and outflow. Latest HRRR guidance still showing something
along this line of reasoning as well.

Model trends all still pointing to the initial push of showers and
thunderstorms really getting going between 21Z today and 03Z
tonight. However, on Friday, guidance appears to be a little slower
with the timing of the first parent upper circulation lifting out of
Colorado now, in effect, shifting any Friday heat-of-the-day
convection (and severe potential) in the warm sector/along the warm
front further south of this CWA. Plenty of clouds and cooler
conditions in and out of rain on Friday really limiting MLCAPE and
MUCAPE over this CWA. Right now, looking like areas of general
shower and thunderstorm coverage over this CWA on Friday.

&&

.LONG TERM /FRIDAY EVENING THROUGH WEDNESDAY/...
Issued at 403 AM CDT Thu Apr 25 2024

For the start of the long term, rain will be ongoing, along with a
few possible thunderstorms, as ensembles agree pretty well on the
position of the mid level low at 00Z Saturday over SD/NE area, with
the axis of the negative tilted trough expanding southeastward. This
will be a fairly stacked low at this time to the surface. GEFS/GEPS
indicate a slightly deeper sfc low (988mb) than EC (992mb). North of
this low, a cold front will also be swinging east/southeastward over
the Northern Plains. The low will then track northeastward
(occluding along the way) and forecasted to be over ~eastern SD/MN
at 12Z Saturday. We see a little bit of a difference aloft, as GEFS
keeps the mid level low closed with GEPS/ENS showing an open wave at
this time.

The CWA will be more on the trowel/wrap around part of the low as
increased moisture surges northward and west around the low Friday
evening and more of our eastern CWA by Saturday morning, per GFS
IVT. NAEFS still shows 90%-97% above climo for PW, at 00Z Saturday,
with values 0.75-1", highest values over the James River Valley. NBM
shows this moisture well with pops ranging from 73-97%, highest
around and east of the James River, from 00Z-12Z Saturday. Through
the day on Saturday, the upper wave weakens along with the surface
low as it pushes northeast. Pops chances linger early over the
eastern CWA and decrease slightly by the afternoon as a surface
trough will keep pop chances. Pops range from 25-55% 12Z Sat-00Z
Sunday.

Ensembles agree pretty well on the position of the second trough
that will move in over the Southwestern US along with a developing
Colorado low by 00Z Sunday. The ensembles agree on it becoming a
closed low, but timing is a bit off with GEFS having it form
earlier. By Sunday evening, inconsistencies start to form between
the ensembles on where the axis of the trough ends up (somewhere
over the Central Plains) along with its intensity. At the surface,
this low will push northeast and over the ~Upper Midwest by 12Z
Monday as ensembles show this more of a broad and less intense low
than previous. Pops will increase to 40-75%, highest over south
central SD from 00Z-12Z Sunday and 50-80%, highest east of the Mo
River between 12Z Sunday-00Z Monday as the CWA will again be on the
northern side of the low then wrap around/trowel. Pops decrease west
to east Monday morning. IVT transport indicates this surge northward
of moisture but mainly over more southeastern SD and eastward. EC
EFI indicates this too with values 0.5-0.6 over eastern and
southeastern SD. Chances of light precip (15-25%) return Tuesday as
a weak/low sfc trough moves in from the northwest. Confidence is low
on this due to several days out.

Latest NBM prob of 48hr QPF>0.50" from 00Z Saturday-00Z Monday
ranges from 50-85%, highest over James River Valley and eastward,
which matches up to where that better moisture is. Overall,
probability of CAPE>500 j/kg and shear>30kts remains low, but not
zero, as prob ranges from 5-12% over the eastern CWA Friday evening.
Shear ranges from 20-30kts out of the south, per GFS, with the
better CAPE values over FSD area with our southeastern counties on
the northern fringe of this. SPC does have a marginal risk over FSD
area Friday. CSU is more aggressive on that severe chance extending
further north. So for now, this leaves a chance for general
thunderstorms over the James River Valley. Otherwise, the coolest
day looks to be Sunday as we will be on the cool side of the system,
with forecasted highs only in the 40s/around 50. Temps will
gradually warm next week with highs in the 70s Tues/Wed.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1231 AM CDT Thu Apr 25 2024

Terminals KABR,KATY,KPIR,KMBG

VFR skies/vsbys are anticipated through Thursday morning. Thursday
afternoon/evening may bring an increase in lower cigs from the
south, some of which will fall into the MVFR category. Expect
areal coverage of showers and embedded thunderstorms to begin to
increase late in the day Thursday, as well.

&&

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

$$

SHORT TERM...Dorn
LONG TERM...MMM
AVIATION...Dorn