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268
FXUS63 KABR 182329 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
629 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- There`s a Slight Risk (level 2 of 5) for severe storms along and
  east of the Coteau this evening. The main threats that will accompany
  the strongest storms will be damaging winds and large hail with
  a smaller threat for an isolated tornado.

- Very warm temperatures, gusty winds and a much drier air mass
  combine to produce critical fire weather conditions across central
  South Dakota this afternoon. A Red Flag Warning has been posted
  for areas along and west of the Missouri River.

- Above normal temperatures will continue through Friday with more
  seasonal temperatures for the weekend and next week.

- Showers and storms for the weekend (20-30% chance for
  precipitation).

&&

.UPDATE...
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Issued at 627 PM CDT Wed Sep 18 2024

Aviation discussion updated below for the 00Z TAFs.
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&&

.SHORT TERM /THIS EVENING THROUGH THURSDAY NIGHT/...
Issued at 213 PM CDT Wed Sep 18 2024

As remnant showers from this morning`s activity pull off to the
northeast, thunderstorms have begun to develop over southeast SD
this afternoon. This activity is just ahead of the dry line in a
clash of airmasses. Dewpoints in central SD have fallen into the mid
40s to lower 50s compared to mid to upper 60s dewpoints from the
James Valley east. Most hi-res models don`t develop any severe
weather with these conditions. Still think the slight risk could be
a bit overdone with moderate shear (30 to 35 kts) and relatively
unimpressive CAPE (1000 to 1500 J/kg), but can`t completely rule out
one or two discrete supercells this afternoon or evening east of the
James.

Caa and drier mid level air will see temps fall into the upper 50s
to low 60s across most of the forecast area tonight. More seasonable
temperatures persist into Thursday with highs in the mid 70s to
around 80 degrees. That still puts most locales about 5 to 10
degrees above normal for mid September thanks, in part, to the good
mixing with persistent breezy southwest winds. The cooler
temperatures will provide some relief in terms of fire weather,
however, since min RH is expected to stay above 30 percent in
central SD where gusts will still reach 30 to 40 mph in the
afternoon. A Red Flag Warning remains in effect into this evening
given the much drier conditions and warmer temperatures today along
the Missouri River.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Issued at 213 PM CDT Wed Sep 18 2024

Models are fairly consistent with moving a trough positioned over MO
and Saskatchewan to the east. As this is happening, part of the apex
of the trough moves over SD Saturday afternoon, though there is some
variability in the timing and strength in the models. The models
keep the mid-levels moist on Saturday which aids in the development
of precipitation at the surface. They also show agreement in mid-
level temperature advection, moving WAA in over central and
eastern SD until Saturday morning, when CAA moves in to take its
place. The WAA helps to keep maximum temperatures on Friday around
10 degrees warmer than normal. As the upper-level low moves east
on Saturday, the associated surface front interact with the mid-
level moisture and the CAA. This helps the development of
precipitation Saturday afternoon, with the Canadian model
developing the heaviest precipitation east of the James River
Valley Saturday evening. The GFS is different from the other
models, as it does not develop any precipitation in central or
eastern SD because of its lack of mid- level moisture. Some
clusters suggest that there is a low possibility that the
developing precipitation could be severe, with stronger shear
values. However, instability values will be lower from the lack of
energy available, limiting severe potential. The deterministic
models do pick up on those higher shear values, as the 0.5km model
winds picture stronger winds on the Canadian and NAM Saturday
afternoon. Fairly strong lapse rates will allow these winds to mix
to the surface. The NBM also shows this, with gusts up to 30kts
in counties west of the Missouri River Saturday afternoon.

The models and clusters start to disagree more after Sunday morning,
as they struggle to handle an area of low pressure moving northeast
over UT and CO. Some models have the low being absorbed into the
isobars of the trough located over Saskatchewan and Manitoba,
becoming a shortwave. This then creates more southwesterly flow over
SD. However, other models leave the low as a cut-off and struggle to
incorporate it, creating more zonal flow over SD as they try to push
the low east. By Tuesday, the GFS and Canadian models start to move
a ridge east from the Pacific Northwest, which starts to push into
counties west of the Missouri River on Wednesday. Then with some
variability, models keep the mid-levels dry with CAA until Monday
afternoon, when they move some moisture into central and eastern SD,
as well as moving occasional pockets of WAA and CAA through SD. With
this variability in forcing and lack of lift at the surface, there
looks to be little chance for precipitation to occur after Saturday.
The CAA coming in behind the front on Saturday will help to cool
temperatures at the surface. Because of this, Sunday will see
maximum temperatures about 5 to 10 degrees below normal values.
Temperatures will then start to slowly warm up, and they will be
around average for the rest of the forecast period.
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&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
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Issued at 627 PM CDT Wed Sep 18 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast through the TAF period. Southerly
surface winds will gradually become southwest, then westerly
through the next 24 hours.
-- End Changed Discussion --

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning until 9 PM CDT /8 PM MDT/ this evening for
     SDZ003-015-033-035-045-048.

MN...None.
&&

$$

UPDATE...TMT
SHORT TERM...Wise
LONG TERM...Vernon
AVIATION...TMT