Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 180358
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1058 PM CDT SAT SEP 17 2016

.SHORT TERM...(This evening through Sunday)
Issued at 302 PM CDT Sat Sep 17 2016

Warm late summer/early fall weather continues into Sunday as flat
upper level flow settles over the region. At the surface, high
pressure slides off to the east, allowing return flow to usher in
warm air advection and southerly flow tonight and Sunday. With
southerly winds, lows tonight will be slightly warmer tonight
compared to this morning, holding in the 50s. Scattered mid level
clouds forming across south central SD and western Nebraska this
evening along the thermal gradient will drift east across the
southern forecast area tonight. With such meager low/mid level
moisture, will leave out any mention of precipitation.

With the pressure gradient tightening on Sunday ahead of a boundary,
well mixed conditions and ample sunshine should allow temperatures
to soar well above normal. Think that guidance is a little too cool,
so nudged slightly towards the too warm GFS to improve highs a few
degrees. Winds will be breezy ahead of the front in far southeast
SD, northwest IOwa and southwest Minnesota. Gusts to 30 or 35 mph
will be possible.

.LONG TERM...(Sunday night through Saturday)
Issued at 302 PM CDT Sat Sep 17 2016

Late Sunday night into Monday morning will pose a very small threat
for showers. A Wave will track through North Dakota into northern
Minnesota, which will create some marginal mid level convergence
along and north of Interstate 90. A lack of moisture and instability
likely to preclude development, but a few hints of some very low
CAPE values might allow for sprinkles and very isolated showers.
Highs Monday, Tuesday and even Wednesday will be warm, from the mid
70s to lower 80s.

Tuesday night will see an increased threat for thunderstorm
development, especially along and north of Interstate 90. A weak
wave will move from Wyoming into the central plains late Tuesday
night. This will bring an increase in winds ahead of it, with the
low level jet focusing across southeast SD into southwest MN,
especially after about 3z-6z. The challenge will be moisture. The
strongest convergence in this layer is so far only hinting at a
small amount of increased moisture which leaves a good chunk of the
area capped. As the convergence shifts north some slightly cooler
temperatures aloft should allow for scattered thunderstorms to
develop as the cap is not as suppressive. Will need to continue
watching the trends of the moisture from about 925mb to 800mb in the
models which will gradually increase confidence in placement and
timing of this potential thunderstorm threat. There will be a small
threat for severe thunderstorms, mainly a threat for hail, as CAPE
could be around 1500 J/kg and the 1km to 6km shear is pretty good
with a small amount of turning from 1km-2km and good speed shear
from 2km-6km.

In the outer periods(Wednesday through Saturday), a busy pattern
through the entire period, although some hints this time around that
upper level ridging Thursday into Friday could limit thunderstorm
coverage. But, with the strong low to mid level boundary hanging
around confidence is not high enough to remove pops, so will have
mainly 20 to 30 percent chances on Thursday. The very strong trough
that will gradually move into the Rockies Wednesday into Friday will
move onto the plains Saturday, bringing the threat for rain and
thunderstorms to the entire area Friday and Saturday. Timing is of
course handled a bit differently Friday and Saturday but the strong
trough is fairly persistent. One thing that is becoming more likely
is a chilly pattern Sunday into early the next week, September 24
through the 27th. Something to keep watching.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1053 PM CDT Sat Sep 17 2016

VFR conditions expected through the TAF period. A low level jet
will develop across the area overnight, resulting in low level
wind shear at KFSD and KSUX from 08Z through 12Z. There is a
possibility of a very isolated shower/thunderstorm along the
Interstate 90 corridor through 09Z, though coverage would be too
sparse to include in KFSD TAF.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...
LONG TERM...08
AVIATION...JM



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