719
FXUS63 KABR 122344 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
644 PM CDT Mon Aug 12 2024

.KEY MESSAGES...

- Near normal temperatures on Tuesday, as well as increasing
  chances (20 to 50+ percent) for showers and thunderstorms Tuesday
  night.

- Additional chances for moisture in the form of thunderstorms run
  from Wednesday through early Thursday. Severe storm potential
  looks limited to Wednesday with a marginal risk (1 out of 5).
  With the slow movement of the thunderstorms, periods of heavy
  rain are possible.

&&

.UPDATE...
Issued at 636 PM CDT Mon Aug 12 2024

Aviation discussion updated below for the 00Z TAFs.

&&

.SHORT TERM /THIS EVENING THROUGH TUESDAY NIGHT/...
Issued at 140 PM CDT Mon Aug 12 2024

At 1 PM CDT, skies are partly to mostly sunny and winds are
generally about 5 to 15 mph ranging from being out of the south to
being out of the east. Temperatures are warming through the upper
60s to mid 70s, heading for the low 80s for some.

So, this area of surface high pressure that has been around since
last Thursday looks to finally be chased off to the east later
tonight into the daytime hours on Tuesday, as mid/upper level
heights rise due to an approaching mid/upper level ridge axis. The
ridge axis aloft will be inducing some lee-of-the-Rockies surface
troffing out into the central and northern high plains over the next
24 hours, which will create a return flow pressure gradient as the
surface high shifts east into the Great Lakes region. Suspecting it
will get, at least, breezy (per BUFKIT momentum transfer tool) on
Tuesday, with 15 to 25 mph sustained southeasterly winds (higher
over the James River valley westward and lower east of the James
River valley). Low level WAA is subtle, but it does appear that
there will be a few degrees of low level airmass warming tonight
into Tuesday. So, looking at/expecting a bit wider coverage of high
temperatures getting up into the 80s on Tuesday. Then, there is also
the question of what will all this low level moisture steadily
advecting up from the south do overnight and on Tuesday in regards
to cloud-cover. A pesky low level stratus deck could affect the
realization of Tuesday high temperatures. Finally, as the upper
level ridge axis translates east of the CWA Tuesday night, shortwave
energy pulling monsoonal moisture up into the region will have a
chance to interact with low level jet winds and mid-level WAA to
introduce some 30 to 70 percent PoPs for showers and thunderstorms
across the CWA.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 140 PM CDT Mon Aug 12 2024

The long term forecast will start unsettled on Wednesday, with an
upper trough and associated surface low approaching from eastern
MT/WY. This will bring the potential for some heavy rain and
thunderstorms as it moves east through the area, but uncertainty
remains on where the storms will be. That upper trough will depart
by Thursday night, with ensemble clusters consistent in a building
ridge over the central CONUS starting this weekend and continuing
into next week. This will lead to generally drier conditions, with
temperatures running near or slightly above normal.

Going into the details for Wednesday, the track of the upper trough
and the associated forcing does lead to some concern in how much
rain we`ll get in our CWA. Latest trends in the
deterministic/ensembles is for two areas of increased precipitation
amounts. The first over central/eastern ND (associated with the
stronger/northern shortwave) and a second area to the southeast of
our CWA (southeast SD into NE/IA border region) associated with the
warm front and increased mid level warm air advection. Between those
two areas, we`re still expecting precipitation, potentially heavy at
times, but with weaker forcing, confidence is reduced on the
where/when of the rain. With the setup, severe threat is on the
lower end, with instability in the 1000-1500 J/kg range and shear
around 20kts. Both of those values are at or below the 25th
percentile of our local 2013-2022 severe weather parameter
climatology based on storm reports, thus feel that the severe threat
is limited with the tall/skinny CAPE profile. SPC has a marginal
risk at this time, which seems reasonable based on the current
forecast. Heavy rain looks to be the main threat, with slow storm
motions (15-20mph) and ample moisture (PWATs of 1.75 inches or
higher across the area on Wed). That matches up with the EC-ENS EFI
data, which is highlighting central SD with QPF values in the 0.6-
0.7 range. In addition, latest NBM probabilities of 0.5" of rain in
central SD are around 50% and 25% for an inch of rain. The rain will
shift east with time Wed night into Thursday, as the upper trough
continues to move eastward. There are some differences in the
amplitude of the upper trough and how quickly it departs, which
impacts the intensity of the low and precipitation amounts, but the
overall trend from the ensembles is for the surface low and
associated precipitation to shift to the east and out of the area
during the day on Thursday.

As the ridge builds over the central CONUS, the primary thing to
watch for is waves riding the ridge and dropping southeast across
the region. Ensembles point to both shear and instability increasing
heading into next week, which would led support to storms, if/when
disturbances move through. Being able to predict the timing/location
at this time range is nearly impossible, thus leading to a lot of 10-
20% probabilities of precipitation across the area this weekend into
next week. Overall, expect largely dry conditions outside any
disturbances that move through.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 636 PM CDT Mon Aug 12 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast to start off the TAF period. Models
indicate areas of MVFR/IFR CIGs potentially developing/moving
northward into the region later tonight. For now, have only
inserted a mention of this at KATY where there is better
consistency in this occurring. Will take another look at the lower
cloud potential for the 06Z TAFs and mention this at other TAF
sites if needed.

&&

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

$$

UPDATE...TMT
SHORT TERM...Dorn
LONG TERM...SRF
AVIATION...TMT