Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 141817

Area Forecast Discussion
National Weather Service Sioux Falls SD
117 PM CDT Sat Oct 14 2017

.SHORT TERM...(Today and Tonight)
Issued at 301 AM CDT Sat Oct 14 2017

Today looks to be a cool and showery fall day across the region.
Stratus deck continues to edge in from the south early this morning
with the main trough evident on water vapor imagery over the
intermountain west. Overhead, a 130+ kt jet streak stretches
northeastward into the Great Lakes region. Showers are already
present over Nebraska and are expected to expand in coverage across
our area around and after sunrise as mid level warm air advection
and isentropic lift increase. Latest CAMs continue to advertise the
better shower activity will align along and north of I-90 after the
initial wave of showers pushes north, and thus this is where the
likely to categorical POPs exist. Further south across our southern
counties, expect showers to be more hit or miss in nature until
perhaps the evening hours as the system begins to pull east. High
temperatures won`t warm much this afternoon with extensive cloud
cover in place and winds eventually shifting out of the northeast.
Low to mid 50s will be common with perhaps slightly warmer high
temperatures across our far southeastern counties.

By this evening, the surface low begins to move northeast through
Iowa. As this happens, we begin to lose our isentropic lift and
shower activity will begin to come to an end from west to east,
although latest models have trended somewhat slower with this
process. The lower levels of the atmosphere remain fairly saturated
even as this happens and thus could see some areas of drizzle.
Overall, rainfall totals will range from between a 0.25-0.5 across
the north to near or less than a tenth of an inch across the far

The other point of interest during the evening/overnight period of
the forecast is the increasing northwesterly winds. As the
surface low pulls away, the pressure gradient tightens behind the
front with winds responding accordingly. Increased winds some over
previous forecast with Bufkit soundings indicating some gusts in
the 30 to 40 mph range.

.LONG TERM...(Sunday through Friday)
Issued at 301 AM CDT Sat Oct 14 2017

Mid-long range portion of the forecast will be dominated by dry and
warm weather, as upper jet and associated storm track shifts north
into southern Canada.

Will remain on the cool/normal side for temperatures Sunday, as the
cooler air lingers behind the retreating trough. Should see plenty
of sunshine, though could see scattered cumulus across the northeast
in the afternoon as a subtle trailing shortwave drops southeast into

Modest ridging aloft Monday/Tuesday will bring the aforementioned
warming trend to the region early next week. The ridge flattens by
Wednesday as a trough swings through the Canadian Prairies. Unlike
yesterday at this time, when the Canadian model deepened this trough
and drove a cold front well into the Northern Plains, models are in
better agreement in keeping the jet energy well north of our area,
with just a glancing blow by the associated cool front Wednesday
night. Any cooling is quickly displaced northward again on Thursday,
so all-in-all, model consensus points toward a prolonged period of
above-normal temperatures for the upcoming work week, with any
precipitation chances remaining well north of the area. Given
projected 850-925mb temperatures, would not be surprised to see a
couple of days warm further than currently forecast, in particular
Wednesday and Friday, which could also be a little more breezy in
south-southwesterly flow ahead of approaching fronts. However, given
uncertainties in boundary timing and strength of the pre-frontal
thermal ridge, did not make significant changes to model consensus
at this time.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 117 PM CDT Sat Oct 14 2017

Widespread IFR, LIFR and even some VLIFR conditions plague most
areas near and south of I-90 at early afternoon, trending to
mainly MVFR ceilings toward KMML/KBKX/KHON. Lower ceilings will
continue to expand northward ahead of inverted trough/frontal zone
near the James River valley. Has been some drizzle and a few
showers south, but the main widespread rainfall is expected north
of I-90 through the afternoon and early evening. There could even
be a rumble of thunder, but coverage/confidence will keep below a
mention in the KHON TAF. As the frontal zone works through the
area during the afternoon and early evening, will gradually see
any IFR ceilings raise to MVFR, but northwest winds will become
quite strong behind the front from late afternoon well into the
night, gusting 25 to 35 knots at times. Winds will decouple first
around KHON by 08-09z, then KFSD and KSUX toward daybreak.




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