Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 200345
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1045 PM CDT Mon Jun 19 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 309 PM CDT Mon Jun 19 2017

Quiet weather conditions anticipated in the short term portions of
the forecast. A shortwave pivoting through Minnesota overnight will
bring a weak cold front into the area by daybreak Tuesday.  A few
scattered showers or thunderstorms may graze the far eastern
counties of the CWA along the Buffalo Ridge, but most likely this
activity will stay east.

Winds turn light and variable overnight, which should allow
temperatures to cool into the lower to middle 50s. Would not rule
out minor valley or river fog with the cool temperatures, but have
not included in the forecast ATTM.

Tuesday will be another pleasant day albeit a bit brisk given
northerly winds.  Temperatures will still climb into the upper 70s
to lower 80s.

.LONG TERM...(Tuesday night through Monday)
Issued at 309 PM CDT Mon Jun 19 2017

An active weather pattern is expected by the middle of the week with
a potential for strong/severe storms during the first day of the
astronomical summer on Wednesday. Warm air advection and low-level
moisture will continue to surge from central Nebraska to the
southeast of the CWA Tuesday night into Wednesday. This is in
response of a surface low centered over the South Dakota and
Nebraska border, and its associated warm front somewhere along and
south of the Missouri River Valley. With nocturnal deep shear,
scattered elevated storms cannot be ruled out during the night into
Wednesday morning.

Instability, shear, and moisture increase considerably Wednesday
evening into the overnight hours, as the cold front slides east-
southeast across the CWA. The big question is whether or not the
parcel will break the strong capping inversion developed throughout
the day. The ingredients to support strong to severe thunderstorms
are present. Steep mid-level lapse rates, strong 0-6 km bulk shear
vector from 40-50 knots, along with high instability with MUCAPE
values to 2500/3000+ J/kg, could enhance the threat of strong storms
later in the day. Again, this will all depend on the strength of the
cap. GFS model sounding suggests a weakening cap/cooler 700 mb
temperatures after 00Z Wednesday, albeit the NAM suggests a break in
the capping inversion a bit earlier in the afternoon hours. At this
moment, the greatest risk of thunderstorms looks to be east of a
line from Lake Andes, SD to Madison, SD, to Marshall, MN. SPC Day 3
outlook places most of the CWA under a slight risk for severe
storms. It is definitely a period to continue to watch. With
southerly surface winds, and 850 mb temperatures from 20-30 C,
Wednesday will also be the warmest day of the week. High
temperatures can reach the upper 80s to mid 90s.

Isolated to scattered showers and storms may linger through Thursday
as the cold front boundary moves southeast into central Iowa. Diurnal
heating, and the interaction of this front could lead to another
period of showers and thunderstorms in the evening over northwest
Iowa on Thursday.

Increasing cloud cover, and chances of rain showers return Friday
night into Saturday as a strong shortwave over the Northern Plains
and International Border dives south into the area. Given that most
of the instability will remain south of our area, only scattered
rain showers are expected.

Quasi-zonal flow aloft will prevail through the weekend, leading to
northwesterly surface winds and hence, cooler temperatures. Below
normal temperatures are expected into next week. Highs will
generally be in the 70s, to even mid 60s on Saturday. Low
temperatures will stay in the 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1045 PM CDT Mon Jun 19 2017

VFR conditions and sustained winds at or below 12kt will prevail
through the period. Brief higher gusts possible in north-northwest
flow Tuesday afternoon, mainly east of I-29 corridor.

Potential for elevated showers/thunderstorms with increasing
southerly low level jet Tuesday night currently expected to hold
off until after this TAF period.

&&

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

$$

SHORT TERM...Dux
LONG TERM...05
AVIATION...JH


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