Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 231723

Area Forecast Discussion
National Weather Service Sioux Falls SD
1223 PM CDT Sun Oct 23 2016

.SHORT TERM...(Today and Tonight)
Issued at 345 AM CDT Sun Oct 23 2016

A cold front will swing east of our area by mid morning, leading to
a cooler and breezy day. Under mostly sunny skies highs will range
from the upper 50s through the Highway 14 corridor, to the mid 60s
through the lower Missouri River Valley into our lower northwest
Iowa zones.

A surface ridge axis builds into the region tonight with winds
dropping off. Could potentially get pretty chilly, though
uncertainty lies in the amount of cloud cover across the area. The
NAM drops stratus across our north and east overnight on a
north/northeasterly flow, though the GFS/ECMWF do so to a lesser
extent. In light of the NAM, did boost cloud cover just a bit over
Superblend for the overnight hours. At this point, lows look to run
in the mid and upper 30s.

.LONG TERM...(Monday through Saturday)
Issued at 345 AM CDT Sun Oct 23 2016

Another seasonably pleasant day is in store on Monday. An upper
ridge of high pressure is situated west of the forecast area, with a
mild southeast flow of air in this forecast area. The winds will be
rather breezy along and west of the James River valley, with 925-
900mb temperatures suggesting highs in the mid 50s to lower 60s
across this area.

On Monday night, the moisture profile is still forecast to deepen
after midnight, and a strong frontal zone from 850-700mb generates
along with strong warm air advection in this same layer. Low pops
are still warranted for most locations along and north of I 90,
but with an inversion in place through 1.5-2.0km, the chances for
embedded TSRA now look extremely limited. The limiting factor for
rainfall south of I 90 is a large dry layer in the mid levels,
centered near 3.0km which will likely inhibit measurable precip.
One other factor to be concerned about Monday night are low
temperatures. With a moist southeast flow of air in place,
superblended lows looked too cool for most locations. Therefore
mixed in some raw model values which were substantially warmer,
especially the non bias corrected temperatures.

On Tuesday, the morning hours are still influenced by a warm air
advection regime, with the very strong 850mb frontal boundary
still in our area. This boundary is providing good isentropic lift
in the 300-310k layer, and with a deepening moisture profile,
scattered showers are a good bet generally east of the James River
valley. By afternoon, a well advertised short wave begins to
influence our weather with the various models still in fairly good
agreement with its location and strength. The bulk of the
precipitation chances develop along and east of I 29 on the cool
side of the 850mb boundary, and where the aforementioned
isentropic lift remains the strongest. By now, some moderate
instability coupled with a strongly veering profile develops for
areas south of I 90. Therefore went predominant thunder for those
locations and only isolated embedded TSRA elsewhere. The
atmosphere becomes increasingly stable heading into southwest MN.
The bulk of the short wave passes squarely over the forecast area
Tuesday evening, with high pops warranted throughout the eastern
half of our forecast area with deep layer saturation and a
strongly veering warm air advection profile continuing. In fact
the low level jet is progged to be 35 to 45 knots from I 29 and
points eastward out of the south and southwest. Instability still
looks abundant south of I 90, rapidly waning for locations along
and north of I 90. As the wave exits late Tuesday night and
Wednesday morning, stability increases rapidly and the saturated
moisture depth decreases. Therefore no pops are warranted by
Wednesday afternoon. Temperatures after Monday next week look
rather benign at this point. They will likely be normal on Tuesday
and Wednesday, then slightly above normal Thursday and Friday.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1220 PM CDT Sun Oct 23 2016

Confidence in this forecast a bit low at this time. Stratus over
northeast SD will continue to try to work south, but daytime
mixing likely to slow an southward expansion. Once the sun sets
however winds diminish and turn more north and northeast which may
very well advect this stratus field south and southwest. For now
have not introduced into the taf with anything other than tempo
groups for fog as well as scattered MVFR clouds. As confidence
grows the addition of MVFR ceilings, possibly IFR, will be needed.




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