Area Forecast Discussion
Issued by NWS Aberdeen, SD

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855
FXUS63 KABR 212343 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
643 PM CDT Thu Sep 21 2017

.UPDATE...
Issued at 631 PM CDT Thu Sep 21 2017

See below for an aviation forecast discussion for the 00Z TAFs.

&&

.SHORT TERM...(This Evening through Friday Afternoon)
Issued at 336 PM CDT Thu Sep 21 2017

High pressure has now slid well off to the east, with low pressure
centered over Colorado, with a boundary extending from it northward
over western South Dakota. This boundary will push very slowly
eastward tonight to becoming situated from northwest Minnesota to
south central South Dakota. Instability looks to increase across the
far eastern CWA and into Minnesota later this evening into the
overnight hours, along with a developing 45-55 knot LLJ. May see
some strong thunderstorms develop at this intersection, mainly over
the far northeastern CWA around or after midnight. Quiet conditions
are expected during the daytime hours on Friday as the LLJ
diminishes and the shear weakens.

Will see a decent temperature gradient both tonight and Friday, with
much cooler air behind the front. Lows tonight will range from the
upper 40s over north central South Dakota, to the upper 60s over
east central Minnesota. High temperatures on Friday will range from
the upper 50s over north central South Dakota, to the upper 80s over
northeastern South Dakota and west central Minnesota.

.LONG TERM...(Friday Evening through Thursday)
Issued at 336 PM CDT Thu Sep 21 2017

Fairly good agreement over the long term pattern which features a
western CONUS upper low/trough and an eastern CONUS ridge. This puts
us in southwest flow aloft with several distinct waves lifting into
or just southeast of the CWA before the upper low opens and lifts
over the area Monday. In the low levels at the start of the period
we should be on the northwest side of the surface trough. That means
each wave will generate generally overrunning precipitation so have
minimized the mention of thunder for the most part, outside the
initial round of severe weather that develops friday night. 850mb
temperatures remain between +6 and +14C for the extended, so high
temperatures will be stuck in the 50s and 60s for the next few days.
There does looks like, with high pressure overhead and despite a
trough overhead, no waves passing through, that we will see ideal
radiational conditions Wednesday morning. Thus, lowered
temperatures a notch below blended guidance. Otherwise no
significant changes over blended guidance within the extended.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 631 PM CDT Thu Sep 21 2017

VFR conditions expected to persist into the overnight hours before
the potential for sub-vfr stratus (perhaps even some areas of fog)
sets up. Remarkably high dewpoint air exists at the surface from
the James River valley eastward into MN. Once the surface
trof/cold front begins to slow down over central/northeast South
Dakota tonight and surface low pressure begins to deepen along
it, the potential for low level saturation really ramps up, per
the latest RAP Refresh output. For now, have introduced a low
cloud deck at all four terminals late tonight/early Friday
morning.

There is also the potential for isolated/scattered elevated
thunderstorms tonight at or after 06Z which may travel over/near
the KATY (lesser chance at KABR) terminal before convective
potential refocuses east into MN Friday morning. Low level wind
shear potential exists tonight, as well, at the KATY terminal,
where the nose of the low level jet will be focused.

&&

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

$$

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



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