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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
605 am CDT Thursday Sep 3 2015

Short term...(today and tonight)
issued at 431 am CDT Thursday Sep 3 2015

Another hot and humid day in store as upper level ridging continues
to dominate across the region. Thermal profiles support highs upper
80s to middle 90s...with warmest readings once again through south
central South Dakota. With afternoon dewpoints running around 70
over most areas the heat index will run lower to middle 90s across the
entire County Warning Area. Dew points over our south central South Dakota zones will remain
in the lower to middle 60s...keeping heat indices from climbing higher
than they otherwise would be. Will see winds pick up a bit
today...not exactly breezy...but a little stronger than yesterday as
the gradient tightens in response to a deepening surface trough over
the western portions of the Dakotas and Nebraska.

Tonight a shortwave lifts through the western portions of Nebraska
and South Dakota...while a 35 to 40 knots low level jet develops over
the western two thirds of our County Warning Area. With increasing instability and
lift as the shortwave nears our area cannot rule out isolated to
scattered elevated thunderstorm development through our south
central South Dakota/MO River Valley zones after 06z. It will be another very
mild night with lows just either side of 70.

Long term...(friday through wednesday)
issued at 431 am CDT Thursday Sep 3 2015

Warm and humid conditions will persist into the Labor Day
weekend...with more unsettled pattern for the late week period as
series of middle-upper level shortwaves move across the region in
broad southwest flow aloft. Expect any late night convection
across the southwest County Warning Area to slide north through our far west early
Friday... gradually weakening by midday/early afternoon as the
leading wave lifts off to the north-northeast. Modest surface
destabilization behind this wave could allow for isolated late
afternoon/early evening redevelopment in the far west...but think
we are more likely to see isolated to scattered convection
overnight with strengthening low level jet and Theta-E advection
shifting potential farther east in the forecast area Friday night.

Timing of a second wave a little more uncertain for Saturday...with
NAM about 6 hours faster than ECMWF/GFS/Canadian. In either case
though...western/northern areas again will be a focus for low-Middle
Range chance probability of precipitation through the day...with potential increasing and
shifting farther east Saturday evening with development of stronger
low level jet and continued Theta-E advection. Models showing fair
consensus lifting this focus off to the north-northeast of our County Warning Area
during the latter half of the night...though northeast areas will
continue to see chance of southward development into the low level
jet. Temperatures Friday/Saturday expected to be similar...with
highs middle 80s-lower 90s and lows a couple of degrees either side of
70...though changes in daytime convective evolution could certainly
hold these readings a bit cooler.

Large scale trough lifts out into the northern plains/southern
Canadian prairies for the latter half of the Holiday weekend. Models
showing better consensus on timing of the cold front and associated
precipitation threat...reaching James Valley midday Sunday...then pushing
east of I-29 by early evening and exiting the County Warning Area by around midnight
Sunday night. Precipitation focus will be ahead of the front...more likely
during the afternoon/evening as storms have better chance to become

Could see isolated severe storms with any development Saturday
afternoon/early evening as middle-levels still somewhat dry with lapse
rates supportive of hail growth. Forecast soundings moisten quite a
bit through the evening though...which should lead to more of a
locally heavy rain threat as the storms translate northeast late
evening/overnight. Sunday could be complicated by any lingering
convection/clouds hampering destabilization ahead of the front. That
along with stronger shear trailing the front while any substantial
instability in pre-frontal areas should limit severe threat...though
again isolated strong to severe storms not out of the question if
eastern areas are able to warm sufficiently.

Cold front will bring an end to the rain threat for most by Labor
Day on Monday...with temperatures returning to near seasonal normals
of highs in the 70s and lows in the 50s. Models then swing another
wave into the area from the northern rockies...though little model
consensus on timing of this with 00z European model (ecmwf) much faster than GFS. 00z
European model (ecmwf) also quite a bit different than its previous run...leading to
low confidence for precipitation chances Monday night/Tuesday time frame.
For this reason have deviated little from broad model blend for probability of precipitation
and temperatures Monday night through Wednesday.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 602 am CDT Thursday Sep 3 2015

Some patchy MVFR visibilities through the morning...otherwise VFR
conditions expected through the taf period.


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


long term...

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