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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
1043 PM CDT Sat may 23 2015

Short term...(this evening through sunday)
issued at 344 PM CDT Sat may 23 2015

Weak middle level ridging has quieted down the day across the area with
just a few sprinkles continuing across the eastern County Warning Area. Flow across
the Central Plains a bit disrupted by convective complex across
Kansas and Oklahoma...and support the delay in development of precipitation
heading into the evening hours...per almost every piece of guidance
available. Gradually...this area should divert eastward and weaken
enough to allow low level jet to increase as upper wave/jet streak
in the southern rockies and High Plains builds northward. Not
difficult to picture a couple distinct areas of more solid precipitation
splitting around the fringes of the County Warning Area overnight...southeast across
eastern Nebraska and Iowa along with diverted low level jet and
potential mesoscale convective vortex track...and a secondary area of more concentrated
rainfall lifting into the western Dakota plains. However...enough
lift forcing on nose of drying punch aloft working northward through
the Central Plains later tonight to expect a fairly widespread
precipitation threat. The overall potential for thunder would seem to be
fairly isolated...with fairly moist neutral profiles...and some
elevated instability pushing into the southeastern County Warning Area mainly late

Band of precipitation will continue to lift northward in deeper
southerly flow to start on Sunday...with low level jet veering to
support exit to main precipitation by later morning for most...lingering
some across northwest Iowa. Widespread lower clouds expected to
greet the day...while middle levels progressively dry from the south.
Will work on eroding lower clouds to the south...but concern that
easterly low level flow will keep this from occurring...and limiting
both the high temperatures and lower level destabilization. If anywhere was
more favored for a severe storm by later Sunday would
be generally west of a Chamberlain to Tyndall line...where most
likely to break out and generate up to 1000 j/kg MLCAPE. Overall
deep flow remains quite weak...and only has the greater directional
wind change from lower level easterlies to middle level southerlies to
enhance shear. Even pretty far to the marginal side to
support much past an isolated threat...and not a great fan of the
soundings which contain the shear in a fairly shallow layer.
Profiles do suggest that if can get a supercell to develop...a left
mover would be favored...which brings some marginally large hail
into the picture. Very conditional on being able to destabilize.

Long term...(sunday night through saturday)
issued at 344 PM CDT Sat may 23 2015

The upper low wobbles northeast across the northern plains on
Monday...with front dropping across the forecast area Monday
afternoon and evening. With the main upper low rotating a strong
impulse/vorticity maximum across The Heart of the forecast area...shower
chances increase through the night before activity wanes midday on
Monday ahead of the approaching front. The strongest instability on
Sunday evening peaks around 1000 j/kg MUCAPE across south central South Dakota
and decreases drastically east of the James River. Shear is fairly
minimal in this area...which will keep severe chances low but
marginal severe storms cannot be entirely ruled out here through
around middle or late evening. After midnight...thunderstorm chances
decrease overall.

Another round of shower and thunderstorm activity is possible with
the wind shift Monday afternoon and evening. With a bit more
sunshine and temperatures warming into the middle 70s in northwest
Iowa...elevated cape values bump up as high as 1500 j/kg but
effective shear remains pretty weak. Again...cannot rule out a few
marginally severe storms if the overnight precipitation does not
work over the airmass entirely.

Monday night and Tuesday are looking more uncertain than in previous
runs. Latest model runs are nudging towards hanging back the upper
low into Tuesday...with the GFS and Gem the slowest in shunting the
trough to the northeast. While it seems that the GFS and global Gem
are outliers compared to recent model runs...did place a slight
chance of showers in the forecast for Tuesday.

After a brief break in the weather resumes
late in the week as split flow shifts in favor of the northern
stream dropping a broad trough over the north central states.
Wednesday night through Saturday will see shower and thunderstorm
chances each period as the unsettled moist pattern persists.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1036 PM CDT Sat may 23 2015

Scattered rain will continue to lift northward overnight. Ceilings
will gradually lower to MVFR and eventually IFR through Sunday
morning. Some uncertainty on when shower activity will end...but
likely middle-late morning.

Latest guidance suggests easterly flow may remain in place well
into the afternoon...which may prolong sub-VFR conditions in the
terminals. Quite a bit of uncertainty on any potential afternoon
redevelopment...and have chosen to not mention any precipitation at this


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


Short term...Chapman
long term...

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