Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 130328
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1028 PM CDT Thu Oct 12 2017

.SHORT TERM...(This evening through Friday)
Issued at 415 PM CDT Thu Oct 12 2017

Low pressure will move through the Northern Plains tonight which
will allow cool high pressure to settle south. As the cool front
moves through there will be a brief period of moderate cold air
advection which could bring some late evening early overnight gusts
to 20 mph or so, otherwise not a lot of wind expected with this
boundary. Forcing on the mid level boundary is not good tonight and
the better dendritic support remains in the in central to northeast
SD. There should be a nice band of mid clouds but not expecting
precipitation. To the south on the leading edge of the cooler air
aloft dendritic support is very high, about 500-550mb and convective
support is very weak. Not to mention a very stout dry layer below
about 650mb, so the threat for any precipitation before 12z Friday
is very low. Temperatures will again be mild with lows in the 40s.

Dry layer will continue to be challenge to precipitation development
on Friday as jet entrance and associated frontogenetic axis slips
eastward through the area. At best, cloud base likely around 700 hPa
as band builds southeast, and not exactly efficient profiles
thermally with readings warmer than dendritic and barely a hint of
elevated instability.  All things considered, during period when
better mid-level frontogenesis slips through (mid-morning to early
afternoon), could be enough to get a couple isolated showers down
toward KSUX to KSLB with only a hundredth or two QPF. Weak high
pressure drifting toward central MN will continue to filter low-
level dry air as flow slowly turns northeast and east, and will
likely see a good deal of sunshine spreading in from the north as
well during the day. Highs will probably end up fairly even in the
upper 50s to lower 60s balancing clouds/precip/warmer air south to
cooler and more sunshine north.

.LONG TERM...(Friday night through Thursday)
Issued at 415 PM CDT Thu Oct 12 2017

The most significant feature of the intermediate to longer range
continues to be the precipitation chances later Friday night through
Saturday.

Friday night, the boundary which moved through tonight and stalled
across southeast Nebraska to far southern Iowa will begin to nudge
northward with strong jet pushing into the central Rockies
associated with a positively tilted longwave trough. Cross boundary
flow does increase later Friday night, and enough advection that a
few showers could return south of Highway 18. Fairly strong
agreement that will see a punch of drying through the mid-levels
which spreads over much of the area by later morning and into the
afternoon. Best lift for showers will occur on the nose of this
feature, which suggests higher PoPs a bit quicker in spreading
northeast. With the drying aloft, there will still be 4-5kft of
moisture trapped below a weak inversion, and in zone near inverted
trough across northwest IA back toward southwest MN, could actually
go over to some drizzle for a time before boundary passes eastward
and changes lower levels to cold advection. Still perhaps a rogue
thunder threat in far southern portions of NW IA during the later
morning, but only if can get some high-based development above the
shallow moist layer.  Clouds and precipitation will mean mainly 50s
for highs.  At this point, less than two tenths of an inch QPF with
highest amounts highway 14 and highway 71.

GFS continues to be the speedy representative of operational models,
as well as far and above the quickest member of the ensembles. ECMWF
still a moderate solution and have sided a bit closer to this on
timing, and virtually ignored input from the sluggish Canadian. On
this timing, could still be enough lift and lingering moisture along
mid-level boundary for some showers into the evening, mainly east
central SD across southwest MN. One feature of importance for the
evening will be some strong winds, with increase in mixing tapping
35 to 45 knots of wind energy. Winds will likely stay up much of the
night, but drop off late as weak ridge axis builds toward I-29. It
should drop off quick enough to allow temps west of I-29 and north
of I-90 to fall into the lower 30s.  A bit more wind continues into
the morning across southwest MN toward the Iowa Great Lakes.

Other than the early wind, Sunday will have lots of sunshine and
winds shifting toward the west/southwest. A bit of recovery to temps
with the westerly flow and initiation of warm advection to the mid
50s and lower 60s. Large diurnal fall likely with classic southwest
decoupling Sunday night, and could see a little frost in lower spots
pretty much anywhere around the area with temps dropping to the mid
30s.

Monday through Thursday will be a terrific stretch of weather for
mid October and farming interests - dry, with warm highs and an
extended diurnal range to cool overnight lows. It will be breezy at
times. Could see a bit more high clouds at times with largely zonal
to southwest flow aloft, but should be enough sunshine to go
around.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1026 PM CDT Thu Oct 12 2017

VFR conditions through the period. Mid level clouds at or around
10,000 feet are expected tomorrow. Operational restrictions are
not expected.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Chapman/08
LONG TERM...Chapman
AVIATION...Ferguson



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