Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 290354

Area Forecast Discussion
National Weather Service Sioux Falls SD
1054 PM CDT Fri Jul 28 2017

.SHORT TERM...(This evening through Saturday)
Issued at 256 PM CDT Fri Jul 28 2017

Quiet weather ahead as a ridge of surface high pressure slowly
shifts south from Minnesota into Iowa. This will leave the south to
southeast flow in place with only marginal humidity levels on
Saturday. Suspect that dew point temperatures will be in the lower
to mid 60s which is likely just a bit below normal for this time of
year. With the drier air and fairly light winds lows tonight will
drop down to around 60 in northwest IA and southwest MN while
central SD will see lows closer to 65. Highs on Saturday should
range from the lower 80s around the Iowa Great Lakes to near 90
around Chamberlain.

A weak wave will move into central SD Saturday afternoon and when
combined with surface heating and marginal instability isolated
showers and thunderstorms will be possible. The better chance will
be along and west of the James River Valley.

.LONG TERM...(Saturday night through Friday)
Issued at 256 PM CDT Fri Jul 28 2017

Overall, fairly pleasant weather with mostly dry conditions and
seasonable temperatures are expected for the extended. The best
chance for showers and thunderstorms returns on Tuesday into

Upper level ridge continues to dominate the south-southwestern half
of the CONUS as it amplifies and moves back to the west next week.
While the surface high pressure centered over the Upper Mississippi
Valley area continues to prevail keeping dry weather and seasonal
temperatures into the area; northwest flow aloft will result in a
few weak disturbances over the region.

A weak shortwave will dive south from west-central Dakotas into
southeast SD Saturday night into Sunday, along with a moderate
impulse of energy provided by the upper jet. Model soundings at
KHON/KMHE/K9V9 show an increase in low-level moisture from 850 to
700 mb layer, but models are not in agreement with this disturbance.
The ECMWF and Canadian remain dry while the GFS and NAM suggest
precipitation mainly for the western half of the FA. Therefore, left
low chances during this time frame with isolated showers or storms.

The best chance for showers and thunderstorms looks to be Tuesday
into Wednesday morning as a disturbance/shortwave moves south from
the Northern Rockies along the upper ridge. This will bring a
frontal boundary extending west to east and moving southward across
the CWA through the day. Models are in better agreement with this
system, but still differ in coverage, intensity and timing.

With northwesterly flow aloft prevailing, seasonal temperatures in
the 80s are expected through the period. At this point, the warmest
day is expected to be Tuesday ahead of the aforementioned frontal
boundary, with readings in the lower 90s west of the James River.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1053 PM CDT Fri Jul 28 2017

VFR conditions are expected through the TAF period.




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