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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
1233 PM CDT Sat Apr 18 2015

Short term...(today and tonight)
issued at 355 am CDT Sat Apr 18 2015

The progression of the upper low currently centered over southern
Colorado continues to show a slowing the main focus for
today will be the slower systems impact on precipitation timing and
temperature trends. Strong isentropic lift remains confined to
Nebraska early this morning which has left much of the forecast area
dry so far. While a few stray rain showers will be possible in our
extreme southern counties this morning...expect the main band of
showers and thunderstorms firing along the to finally push into the
Missouri Valley region middle to late morning and lift into i90 around
in the early afternoon.

Temperatures will be tricky to rain will cool or slow
heating during the peak heating hours. Our northeastern counties
will remain dry for much of the day and should manage to reach the
upper 60s or low 70s...however the big question is how much dry
slotting will work into the southern half of the forecast area this
afternoon...which could allow temperatures to quickly rise late in
the day. Also of interest is this region is the potential for decent
late afternoon/early evening instability developing as the
temperatures heat to near 70 and a moist air mass left in the wake
of the exiting frontal showers. Models develop some skinny cape
values as high as 500 j/kg. While shear is very weak...cannot rule
out some scattered storms firing middle to late afternoon with small
or even marginally severe hail south of i90.

While the bulk of the forecast area remains largely within the dry
slot of the large storm system tonight...scattered showers and
thunderstorms will remain possible but the hail threat will diminish
after midnight. Could see greater coverage along the western fringes
of the County Warning Area late evening and shifting eastward overnight with the
cold front advancing through the region...but will leave high end
chances for now given timing is still a bit uncertain. All
said...the forecast area can expect anywhere from 0.4 to 0.75 inches
of total rainfall today and tonight. Lows tonight will be in the middle
40s to lower 50s.

Long term...(sunday through friday)
issued at 355 am CDT Sat Apr 18 2015

The Sunday through Friday period seems destined to be a cool
contrast to the recent mild weather with a digging western Great
Lakes trough which will gradually shift east...but with reinforcing
waves helping to block significant plains ridging...highs are going
to stay mostly in the 50s.

Showers will linger then end Sunday as the cold front passes beyond
the area. A few showers may develop in the cool air northeast half
Monday as a secondary wave speeds down the back side of the trough.
Windy conditions behind the front will persist Monday with this
secondary wave...perhaps with winds reaching advisory level speeds.

Cool surface ridging along with the upper trough moving to the east
should keep it rain free over the area Tuesday through Thursday. On upper low approaching from the southwest
could bring a rain threat. For now...the GFS and ec keep the threat
tame and mainly south for completely different reasons in different
patterns. The GFS in fact shows a pattern that could bring the low
right at the area and bring a rather significant rain event...except
that a trailing Canadian border wave it shows flattens the ridge
ahead of the trough and keeps the system from coming nearly as far
north as it would otherwise. However there have been a couple cases
recently with the GFS overdoing the ridging east and northeast of an
upper low...and so far the GFS shows no consistency on this pattern.
This is day seven to probability of precipitation will be modest and mainly south.


Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1230 PM CDT Sat Apr 18 2015

Narrow corridor of rain continues to slowly lift north this
afternoon. Generally...brief reductions to MVFR or locally IFR
ceilings/visibility are possible...especially for fsd/sux this

This precipitation will lift north of the terminals late this
afternoon or early this evening. Stratus should prevail through
the overnight hours...and would not discount the potential for
drizzle later on. Low level trough will pass through the area
overnight. Scattered showers may accompany this front...but
conditions will quickly improve after daybreak. Once surface
trough swings through near daybreak...gusty northwest winds will
prevail Sunday morning.


Fire weather...
issued at 355 am CDT Sat Apr 18 2015

Fire weather may become an issue Sunday and Monday because of
strong winds with the cooler air. Significant rain today and
tonight could affect that outlook but for now will have the
Prospect of fire danger going to very high in some areas.


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


Short term...
long term...
fire weather...

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