Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 280347

Area Forecast Discussion
National Weather Service Sioux Falls SD
1047 PM CDT Mon Mar 27 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 302 PM CDT Mon Mar 27 2017

High pressure will be the dominant feature tonight as it extends
from south central Canada through the eastern plains. Winds will be
light, and will shift to an east to southeast direction as the night
progresses. There are two things to watch for, first is whether
clouds will erode heading deeper into northwest IA. Second is
any fog formation. It is doubtful whether the stratus will
completely erode in much of northwest IA. That said, the back edge
of the stratus will likely dissipate around sunset along highway 60
including Sioux City leaving a mainly clear sky this evening, with
cloud cover further east around Spencer and Storm Lake. As the
boundary layer flow then shifts to the east, am concerned that some
the stratus may reform over the western sections of northwest IA
later tonight as it backs in from the east. The RAP13 900mb
relative humidity has a good handle on the current stratus field,
and was used for this scenario later tonight and early Tuesday.

With the light winds, areas of fog could once again develop,
especially for areas along the edge of the stratus field in our
eastern zones, then expanding into the stratus areas heading into
early Tuesday. So some fog could encompass many of our eastern zones
by late tonight especially in terrain driven areas such as river
valleys, and also in south central SD along the MO River corridor
with the upslope flow in that area.

Lows tonight will be seasonably mild with readings in the 30s. Any
fog will likely be of shallow depth again, burning off in the mid
morning hours. But deeper moisture will then move into our area
ahead of the next upper low producing increasing cloud cover from
west to east. However with the continued east to southeast fetch of
low level air, the lowest layers may remain a bit dry for much of
our forecast area, so precip chances will erode in our western
zones. Only have measurable pops for light rainfall basically in
Gregory county in the afternoon. Highs on Tuesday will generally
range from 55 to 60.

.LONG TERM...(Tuesday night through Monday)
Issued at 302 PM CDT Mon Mar 27 2017

While the pattern appears to be a fairly busy one Wednesday through
Monday much of the activity should stay to the south across parts of
Nebraska, Iowa, Kansas and Missouri. At this time our better chance
for rainfall will come Tuesday night into Wednesday as low pressure
aloft moves through Kansas into Illinois. While a little thunder
is not impossible the threat is too low to mention. The better
chances for rainfall will be along the Missouri River into
northwest Iowa where a quarter inch of rain will be possible. A
series of waves moves through after this but at this time the main
affects will be to the south of the area. Not to mention some
concern with consistency in timing and placement of this energy.
In general looking at above normal temperatures, not by a lot, but
highs in the 50s and lows in the 30s. There are some hints that
readings another 5 to 10 degrees warmer will be possible by Sunday
and Monday so will monitor those trends the next few days.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1031 PM CDT Mon Mar 27 2017

A few areas of concern tonight. MVFR stratus in northwest Iowa
continues to retreat. Models suggest that this will largely remain
south of the Highway 20 corridor tonight into much of Tuesday,
then lift northward after 00z Tuesday evening with the approach of
the next weather system. Will leave out of the KSUX TAF through
04z. With the light winds and low level moisture in place, expect
areas of fog to develop in the early morning hours for most areas,
with the exception of the James Valley area. Visibility will drop
as low as 1 to 4 miles. South central SD may also see some fog
develop, but this will likely be more spotty. Fog will lift by




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