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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
632 PM CDT Thursday Aug 27 2015

Short term...(this evening through friday)
issued at 307 PM CDT Thursday Aug 27 2015

Active period tonight with a series of short waves moving across a
very moist environment. Have dealt with some isolated storms that
have produced a narrow band of of rainfall of 1-2 inches just south
of Marshall Minnesota. Expect this activity to shift east of the
area in the next hour or so. Have seen some at least partial
clearing across southeastern South Dakota allowing temperatures to
warm to near 80 degrees along the Missouri River valley. This has
resulted in sb cape values increasing to near 2000 j/kg of cape. As
the initial leading wave approaches from the South West...expect
discrete convection to develop after 22z across the Nebraska/South
Dakota boarder. With the initial convection...could see a few
storms approach marginally severe criteria with wind and hail as the
primary threats.

The focus thereafter shifts towards the overnight period as very
moist environment remains in place across the forecast area.
Precipitable water is near 2 inches across the forecast area...near
climatic record levels. Tall thin cape profiles will likely produce
very efficient rain processes across the area. Have heavy rain
mentioned across the southeastern quadrant of the forecast area.

Concerned about secondary wave that is expected shift eastward south
of the initial leading wave. This system could disrupt inflow into
the complex of storms...and reduce areal extent of stratiform
region. Therefore the heavy rain is somewhat conditional. Given we
are expecting a prolonged event...will have to watch locations for
training and the potential for river flooding downstream.

Have squashed diurnal range in terms of temperatures tonight into
tomorrow with precipitation and clouds. Forcing shifts east through
the area on Friday...but with soupy air lingering across the eastern
half of the forecast area...will likely have fair amount of stratus
limiting the warming.

Long term...(friday night through thursday)
issued at 307 PM CDT Thursday Aug 27 2015

Rather quiet conditions in the medium and extended portions of the
forecast. Only a few minor concerns into the middle of next the pattern generally suggests dry conditions and above
normal temperatures.

One area to monitor is the degree of stratus lingering over the area
Friday night into Saturday morning. Models typically too
aggressive pushing the cloud cover eastward. Some signs that even
if stratus does slide just away from the County Warning Area after midnight...fog
could develop on the western flank and linger into Saturday
morning as winds remain light.

Through the middle of next week a broad ridge will dominate the
eastern half of the Continental U.S....with troughing centered over the Pacific
northwest. This will keep the area under a warmer southwesterly flow
aloft. Would not be impossible to see an isolated storm each
afternoon at peak heating...but feel chances are far too low to
include at this time. Temperatures will reach the middle 80s to lower 90s.


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 630 PM CDT Thursday Aug 27 2015

Occasional showers and thunderstorms will reduce ceilings and
visibilities this evening and possibly overnight into the MVFR
range...and in the heaviest of rainfall...IFR is possible. Late
tonight after 06z...the low clouds and stratus are a question mark
as to just how low they may go. The various model humidity time
sections and soundings are quite bullish on IFR to lower end MVFR
conditions late tonight and Friday morning. That
observations upstream are yet to develop this sort of ceilings. So
confidence is a bit low on the determination of stratus late
tonight and Friday morning.


Fsd watches/warnings/advisories...
South Dakota...none.


Short term...
long term...dux

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