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545
FXUS63 KABR 241727 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1227 PM CDT Mon Jun 24 2024

.KEY MESSAGES...

- Hot and humid conditions set in today with afternoon
  temperatures climbing into the 90s and dew point temperatures
  in the upper 60s to low 70s. This will lead to heat indices to
  top out around 100 degrees mainly in the James Valley where a
  Heat Advisory will remain in place.

- A small chance for an isolated strong to severe thunderstorm
  will be possible late this afternoon into tonight and early
  Tuesday. Highly uncertain where any activity will evolve given
  highly inhibiting ingredients are in place.

- Two rounds of moisture for late in the week. Mid-level warm
  advection related convection for Wednesday night/Thursday
  (30-50%) and low pressure system early Friday (30-60%).

- Near normal temperatures through the week. Cool temperatures for
  the upcoming weekend.

&&

.UPDATE...
-- Changed Discussion --
Issued at 1224 PM CDT Mon Jun 24 2024

See updated aviation discussion below.

UPDATE Issued at 1010 AM CDT Mon Jun 24 2024

Seeing some very light shower activity across the far eastern part
of the area this morning, but that looks to exit to the east by
midday or so. No changes made to winds or temperatures at this
time.
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&&

.SHORT TERM /TODAY THROUGH TUESDAY AFTERNOON/...
Issued at 507 AM CDT Mon Jun 24 2024

The main challenges in the short term revolve around today`s heat
and high humidity and convective potential later today into the
overnight hours tonight. First off this morning, our forecast area
remains relatively quiet and mild with temperatures in the 60s to
low 70s. This will help in part set the stage for a hot day across
the CWA. Scattered convection has been affecting mainly parts of ND
early this morning as some shortwave energy crashes over the top of
an upper ridge that remains in place for the moment across the
region. A couple of isolated showers could scrape across our far
northern areas, along the ND/SD border, the next few hours, but
overall dry conditions are expected to prevail as the daytime hours
kick off.

Hot temperatures and high humidity will be the main themes in our
weather today across this forecast area. That upper ridge axis will
shift eastward into MN and the Western Great Lakes today. At the
sfc, parent low pressure will track west to east across Manitoba
today. A secondary area of low pressure across SD this morning with
an associated warm front are progged to trek east-northeast across
our forecast area and be in the vicinity of our far northeast zones
by the midday/afternoon hours. A weak cold front will trail behind
these features across then central Dakotas around midday and shift
eastward into the eastern Dakotas and western MN by early this
evening. This should put some parts of our forecast area in the warm
sector at a reasonable time frame to maximize temperatures this
afternoon into the mid 90s. In addition to that, after the
aforementioned weak cold front swings through and winds turn
southwest to northwest, we should get a reasonable amount of mixing
to also aid in warming temperatures. A moisture rich air mass will
be advecting into the area with sfc dew point temperatures warming
into the upper 60s to low 70s. This will produce heat indices that
approach or exceed 100 degrees for a period of time this afternoon,
especially across the James Valley and certain locales either side
of the Valley. For these reasons, have continued with the existing
Heat Advisory but also expanded it to some extent west and east to
include locales like Pierre, Kennebec, Clark, Watertown and Milbank.

The one uncertain part of the today`s forecast revolves around
convective potential. Several different scenarios for storms will be
possible across the Dakotas/MN region later today into tonight.
Model discontinuity is playing a part into the overall low
confidence in this part of the forecast. First, our forecast area
will see an expansive EML develop during the day with 700mb
temperatures warming to between +14C to +16C. So, this cap should
really be a driving factor in precluding any convective initiation
across our area. The previously mentioned moisture rich air mass and
very warm temperatures at the sfc combined with steep mid level
lapse rates will lead to an extremely unstable environment with
MLCAPE values of >4000-5000 J/kg across our eastern zones this
afternoon. There will be sufficient westerly deep layer bulk shear
up to 40kts in our far east and/or higher just to the east of our
CWA. Some CAMS suggest isolated could initiate late this afternoon
near the vicinity of the sfc low/triple point/warm front in far
northeast SD/southeast ND/western MN and perhaps shift southeastward
along the warm front and instability gradient. This remains very
uncertain given the large inhibition in that strongly capped
environment that expected to be in place. If there are any storms
that do get going over in that area, large hail and damaging winds
will be the main threats, but can`t rule out an isolated tornado as
well on the MN side. Trends will just have to be watched closely as
we progress through the afternoon.

The remainder of the forecast remains a bit unsettled initially, but
overall drier and cooler conditions are expected to take hold. Some
convection will be possible across the Black Hills and western SD
behind the aforementioned cold front this evening. That frontal
boundary is expected to stall somewhere in the vicinity of southern
SD or the SD/NE border area. A little bit of leftover shortwave
energy progressing through mid level flow across southwestern SD
which may aid in allowing the western SD convection to persist long
enough to reach parts of our western/southwestern zones late this
evening into the overnight. Again, very uncertain with low
confidence in this evolving as well. There will be a fair amount of
low level dry air working it`s way into the area behind the frontal
boundary. Sfc high pressure begins to build in on Tuesday which
should prove to a be a drier, cooler more comfortable day across the
forecast area.

&&

.LONG TERM /TUESDAY EVENING THROUGH SUNDAY/...
Issued at 507 AM CDT Mon Jun 24 2024

Start the long term in a west-northwest flow regime with a northwest
flow wave crossing the far northeast CWA early Wednesday. There will
be little surface reflection as a high pressure system expands out
of North Dakota, with just some mid-clouds for the northeast. A
ridge moves in from the west for Wednesday/early Thursday though
this comes with some mid-level moisture and a subtle shortwave that
loops up over the ridge resulting in some weak ascent. Thus, chances
for moisture proceeding west to east on the order of 30-50%. NBM
probabilities for 0.25 inches is only 20% down by Pierre to about
40% across far northeast SD/western MN. The flow becomes
southwesterly as an upper low moves into Montana, at which point we
see a divergence between how deterministic guidance handles its
progression. Clusters show a lot of spread as well, though the end
result is still a low pressure/cold frontal system across the
Dakotas for additional chances at moisture and an NBM CWASP peaking
around 60 percent Friday afternoon.  We`re also seeing improved
confidence for cool conditions next weekend, with 850mb temperatures
bottoming out around +5 and +10C Saturday. NBM ranges for highs/lows
are only is only about 5 degrees Saturday/Sunday morning with the
potential for temperatures to drop below 50 (10-40%).

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
-- Changed Discussion --
Issued at 1224 PM CDT Mon Jun 24 2024

Terminals KABR,KATY,KPIR,KMBG

An area of MVFR cigs over north central South Dakota will
gradually dissipate by early afternoon. Otherwise, for the most
part, VFR conditions will prevail through the the TAF period.
There is a small chance for a few thunderstorms late this
afternoon and evening across the far eastern part of the area.
Periods of MVFR vsbys will be possible with any thunderstorms.
There is also a chance for some additional shower development
across mainly central South Dakota late tonight into Tuesday
morning.
-- End Changed Discussion --

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 7 PM CDT this evening for SDZ006-017>023-
     035>037-048-051.

MN...None.
&&

$$

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