Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 182324

Area Forecast Discussion
National Weather Service Sioux Falls SD
624 PM CDT Fri May 18 2018

.SHORT TERM...(This evening through Saturday)
Issued at 401 PM CDT Fri May 18 2018

Active weather expected tonight into the weekend with a frontal
boundary draped across the region, with an active southwest upper
level flow directing waves through the central Plains. A fairly
significant change was made to the forecast for tonight and
Saturday, with models trending weaker and further south with the
boundary this evening and tonight. Likewise, the main upper low
churning over Colorado is tracking further south. The result is
for focus of the lift and and forcing to remain near or south of
the Missouri Valley (in Nebraska). With this in mind, have trimmed
back pops significantly to the north of I-90, and decreased the
QPF amounts for tonight and Saturday for most locations.

Tonight, boundary draped near the I-29 corridor will continue to
advance eastward through western Iowa and Minnesota through early
evening with very little fanfare. Isolated to scattered showers with
a few thunderstorms will be possible this evening, however the
cloudy skies today have minimized the overall instability. Most
areas will see a few light sprinkles at best. After midnight, the
surface low lifts into southwest Kansas with strong vorticity
lifting into central and northern Nebraska. A better chance of
showers and thunderstorms will begin lifting northward into the
MIssouri Valley mainly after midnight. Will keep chances for storms
along and south of I-90, but could very well see much of the
forecast area remains dry overnight.

Saturday will continue to see the surface low advance into northeast
Kansas with the frontal boundary well south of the area. Cloudy
skies and cooler weather is expected with breezy northeast winds.
Scattered showers will remain possible primarily along and south of
I-90 with the stronger forcing remaining south just  south of the
forecast area. Best chances for showers and storms remain near the
Missouri Valley and northwest Iowa, but with marginal instability
and pretty weak shear, the severe threat is very minimal. Do not
expect it to be a total wash-out on Saturday even for areas near
Missouri Valley, but sporadic rain showers with brief heavy
downpours are expected. With the better moisture and instability
remaining to our south, QPF amounts for the

.LONG TERM...(Saturday night through Friday)
Issued at 401 PM CDT Fri May 18 2018

Slow moving upper low continues to drift eastward across the
central and northern Plains Saturday night through early Monday
morning as it weakens. But the unsettled pattern will keep
scattered showers in the picture each period. Again, all day rain
is not expected, but rather periodic showers tracking through the
region with the broad scale unsettled conditions. With the better
forcing, moisture, and instability remaining to our south, QPF
amounts for the duration of the event have been decreased some,
but could see around an inch or two total south of I-90.
Temperatures will remain cool into Monday with highs mainly in
the 60s.

A brief return of warmer and drier weather arrives for Tuesday as
a ridge quickly tracks across the Plains, however the active
weather pattern directs the next trough towards the region
Wednesday into the end of the week. Still a lot of uncertainty in
the strength and timing of waves, but the pattern supports chances
for showers and thunderstorms each period. Not enough confidence
to differ from the going scattered pops.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 622 PM CDT Fri May 18 2018

Only a small chance for rain and thunderstorms through the night,
althought chances along the Missouri River will be greater. MVFR
ceilings will settle into the area from the northwest with most of
the area under an MVFR ceiling from 9z to 18z tomorrow. The best
chance for rain and isolated thunderstorms will be late tonight
into tomorrow.




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