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207
FXUS63 KABR 270943
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
443 AM CDT Thu Jun 27 2024

.KEY MESSAGES...

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- Chances for showers and thunderstorms(40-70 percent) will spread
  from central into northeast South Dakota and west central Minnesota
  this morning into this afternoon.

- A more significant round of thunderstorms is expected to develop
  late this afternoon in western South Dakota and move into central
  South Dakota this evening. Large to very large hail, damaging
  winds and a few tornadoes will be possible. There remains an
  Enhanced Risk (3 out of 5) for severe weather West River and an
  Marginal/Slight Risk (1-2 out of 5) for locales farther east.

- Friday`s severe weather potential is conditional; hinging on the
  position of a cold front. Currently, portions of central and
  northeast South Dakota and west central Minnesota are included in a
  Marginal Risk for severe weather (1 out of 5).

- Another opportunity for showers and thunderstorms will arrive
  later Sunday into Monday (30-70% chance of measurable rain).
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&&

.SHORT TERM /TODAY THROUGH FRIDAY AFTERNOON/...
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Issued at 441 AM CDT Thu Jun 27 2024

The main focus in this period will be on thunderstorm chances today
into tonight and the associated severe weather risks that are
expected. Early this morning, we`re already seeing sub-severe
showers and storms across our western zones, in central SD. Mid-
level warm air advection and increasing low level moisture transport
along with a mid-level impulse in the 500mb flow is coming together
across the central and western portions of SD early this morning
leading to this convection. CAM`s and other hi-res short range
guidance continues to show this activity shifting east through the
pre-dawn hours, reaching the James Valley closer to daybreak. These
generally sub-severe showers and storms will more or less persist
across our eastern CWA through the morning into the afternoon hours,
perhaps becoming more widely scattered with time.

Our attention will then turn back to our west by late in the day
into this evening as another round of thunderstorms are expected to
develop across the western Dakotas and stumble eastward into our
western zones. These storms will be packing a punch with a fairly
high probability of seeing all types of severe weather risks. The
atmosphere across the western Dakotas will become primed for storms
to develop during the afternoon hours. An upper ridge in place
across the Dakotas will start to weaken as a mid level low over the
PacNW shifts east into the Northern High Plains. This will aid in
strengthening a lee side sfc low across eastern MT. This low is
progged to shift into the western Dakotas late this afternoon. Mid
level lapse rates will steepen in response to diurnal heating
leading to MLCAPE values 2000-3500 J/kg with deep layer shear
between 40-50kts. In addition to the sfc low aiding in kicking off
convection, a trailing cold front will sweep east across eastern
MT/WY into the western Dakotas and help in forcing additional
convective development. It is worth mentioning that farther south,
across our southwestern zones, there is expected to be a stronger
cap in place late this afternoon and evening with 700mb temps of
+13C to +14C, so that could throw a wrench into the whole convective
initiation.

Storms that do kick off will grow upscale into supercells that will
initially favor large to very large hail. Favorable low level shear
in the presence of the sfc low will also be conducive to some
tornado development. These supercells are anticipated to push into
our West River zones and perhaps eventually evolve into an organized
MCS which would eventually pose more of a damaging wind threat with
time going through the evening hours. Beyond the mid to late evening
hours, the big question will be what coverage will the storms have
and what will be their longevity. Guidance suggests as they progress
farther east into our CWA, they will be encountering a more stable
environment which would lead to diminished severe weather potential
for locales in the James Valley and points east. We`ll just have to
see how trends play out after the convection initiates later today.
Due to the initial chances for severe weather late this afternoon
and early evening, SPC has continued to hold with an Enhanced Risk
(3 out of 5) for severe weather across the western Dakotas, which
also includes our zones west of the Missouri River. A
Marginal/Slight Risk (1-2 of 5) areas remain in place east of the
Missouri River into the James Valley and on eastward into west
central MN for potential convection later tonight.

The remainder of the period will begin to gradually improve and calm
down. There will be some leftover chances for showers and storms
into the first part of Friday, especially across our eastern zones.
Some CAM`s even would like to generate afternoon convection across
our east. At this point, have left it mainly dry upon further review
of new guidance. Temperatures through the period will remain
seasonal. Rather warm and humid conditions are likely to prevail
with some improvement in the high humidity values late in the period.
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&&

.LONG TERM /FRIDAY EVENING THROUGH WEDNESDAY/...
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Issued at 441 AM CDT Thu Jun 27 2024

The overall pattern this weekend and into next week features the
upper trough overhead departing with west/northwesterly flow aloft
Saturday/Sunday. Late Sunday, a ridge is moving in from the west,
and we`re into a southwest flow regime by early Monday. Thats ahead
of another shallow upper level trough that moves overhead Tuesday.
This trough, broader than the previous, lingers across the area for
mid-week. This fairly progressive pattern will give us several
opportunities for inclement weather.

So, for Friday evening, the first front has moved into
western/central Minnesota (outside of the CWA), with a secondary
front coming into north central South Dakota as well. This may also
provide the focus for an additional round of weaker convection. A
few CAMS and NAM BUFKIT profiles hint at some mid-level instability
associated with rapid cooling above 850mb, though with a substantial
and deep dry subcloud layer. The majority of the low level cold
advection follows this secondary front, with 850mb temperatures
around +14 to +18C at 00Z Saturday falling to +5 to +10C by 18Z
Saturday. The overnight gradient is also about 10mb across the
state, so as previously mentioned, mixing will keep temperatures
from bottoming out until the high pressure system moves overhead
Saturday/Saturday night.

A tight gradient develops on the backside of that high however, and
by Sunday afternoon winds will have increased markedly. The gradient
across the state tops out around 20mb, with 1/2km winds increasing
to 40-45kts south to north Sunday night. NBM winds are appropriate
at this timerange, but some enhancement with this direction up the
James valley can probably be expected as well. As mentioned in the
previous discussion, probability of advisory level winds are
confined to Corson/Dewey counties at this point though.  Low level
jet and mid level warm advection also brings with it additional
chances for moisture along this gradient Monday morning. The surface
low lingers into the day. NBM CWASP increases to around 60-70%,
though with the presence of an elevated mixed layer (700mb
temperatures between +12 and +15C).
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&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1239 AM CDT Thu Jun 27 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are still expected to persist into the early
morning hours at all 4 TAF sites. Showers and thunderstorms will
begin to develop and spread across central South Dakota before
daybreak with MVFR/IFR cigs/vsbys setting in at KPIR/KMBG with
the onset of the rainfall. These conditions will spread east into
KABR/KATY terminals by mid morning. Expect these conditions to
prevail through the majority of this remainder of this forecast
period.

&&

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

$$

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