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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
630 am CDT sun Sep 21 2014

Short term...(today and tonight)
issued at 404 am CDT sun Sep 21 2014

Cool high pressure will continue to expand southeastward across the
northern and Central Plains today and tonight. North northwest winds
will also persist through the day...but will remain generally around
15 knots or less. While abundant sunshine is expected...the arrival of
a cooler airmass will result in afternoon temperatures around 10
degrees or so cooler than yesterday. will overall be
quite a nice late Summer day with highs in the upper 60s to lower

With the surface ridge passing over the forecast area
tonight...winds will decrease and begin shifting to a more southerly
direction by daybreak Monday. With continued clear skies and light
winds...temperatures low should fall back into the 40s...however
with weak return flow developing late...readings will not completely
tank. Expect lows in the low to middle 40s...warmest in south central
South Dakota where southerly winds kick in earliest.

Long term...(monday through saturday)
issued at 404 am CDT sun Sep 21 2014

Monday will be a transition day with high pressure moving off to the
east and an upper low approaching from the west. Southerly flow will
increase through the day...with it becoming breezy west of the James
River by afternoon. Still think it will be a mostly sunny day...with
clouds slowly increasing from west to east late in the day into the
overnight. Did bump highs up a bit...with most locations in the low
to middle 70s. Forcing and moisture will increase ahead of the upper
low on Monday night. Antecedent airmass will be quite
shower potential will probably be slow to push east...with the best
threat west of Interstate 29 Monday night...spreading across the County Warning Area
Tuesday into Tuesday night.

Precipitable water values do increase to around 2 Standard deviations above normal
and isentropic lift and positive vorticity advection ahead of the wave will provide a period
of decent lift. System does seem to lack persistent deep moisture
though...with mean layer relative humidity values never getting too high. So will
keep probability of precipitation in the high chance low likely category...with the thought
that we will see off and on scattered showers Monday night through
Tuesday night. Overall quantitative precipitation forecast amounts should remain around a quarter
inch or less...although isolated higher amounts are
possible...probably towards the Missouri River area. Instability is
pretty meager...although there are periods when we may have just
enough elevated instability to get a thunderstorm. So while showers
will be most prevalent..can not rule out an isolated thunderstorm or
two this period. Given the cloud cover and showers...Tuesday will be
cooler with highs mainly in the 60s. Would not be surprised if we
end up a bit cooler than currently forecast.

Better model agreement today on the evolution of this upper low as
we head into middle week. Now looks more probable that things stay more
progressive with the moisture and forcing pushing east of the
area...thus will just carry some low probability of precipitation on Wednesday...with the
best chance of seeing a shower east of Interstate 29. Should see
some breaks of sun develop from west to east through the day as
well. Did bump highs up some to account for this...with low to middle
70s likely.

Thursday into Saturday should see upper ridging over the
plains...allowing for partly to mostly sunny skies and above normal
temperatures. Did nudge high temperatures up a little...with
readings in the middle 70s to around 80 likely. If current trends
continue may even need to bump these up a few more degrees as we get
closer. So overall looking like a nice period of weather from middle
week into the weekend...with the one caveat that it will probably
end up pretty breezy with a decent pressure gradient setting up over
the plains.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 630 am CDT sun Sep 21 2014

VFR conditions are expected through the taf period.


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


Short term...
long term...chenard

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