Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
658 am CDT Wednesday Jun 3 2015
Short term...(today and tonight)
issued at 407 am CDT Wednesday Jun 3 2015
Compact middle level wave continues to work across the area this
morning...along with associated convective blob featuring leading
cellular development and a well developed stratiform area/mesohigh.
Cold pool should continue to drive development at an accelerated
rate eastward...working with elevated cape of 1000-1500 j/kg at the
leading edge. Could see a couple of cells threaten some small hail
in the predawn hours along the leading line...but Mode has been
generally low centroid and minimal time spent with any elevated
core. Will see the mesoscale convective vortex with this convection track slowly east and
northeast across the County Warning Area toward SW Minnesota through midday. Stratiform
region should diminish some heading toward the early morning...but
this upper center should focus as least some scattered showers and
thunderstorms into midday as it exits the area.
Overall...somewhat challenged by fact that models are struggling to
replicate reality. However...seems that RUC has most accurate
picture of the short term in terms of precipitation coverage as well
as boundary locations...and by late day...the frontal boundary which
is back across northern South Dakota extending from low pressure in
southeast North Dakota is expected to make steady pace
southeast...slowing up a bit by late afternoon to a location near a
kmjq to klcg line. Other models are much further northward...but
trend of 06z NAM was to settle southward. Much will depend on
location of the synoptic frontal boundary by middle to late afternoon
as to where a risk for additional development will occur. Cannot
fathom the extreme instability /2000-3000 j/kg MLCAPE/ that several
models show along the boundary...and rather see that slight ridging
behind morning system during the day will be more than enough to
limit convection in a environment of lesser instability. Will kick
up the convective chances south of a Vermillion to Windom line by
late afternoon...and gradually ease southward in the evening.
Outside chance for an isolated severe storm with hail/wind through
the lower Missouri Valley...but shear is quite weak to expect this
to be the case...with the instability values already a bit in
Confidence in lesser convective threat overall is a bit stronger for
tonight...as dominance of the boundary between I-80 and I-70 to
convective focus will mean that chances should be limited overnight
to the far southern County Warning Area. More stable lower level north to northeast
flow will mean middle 50s north to lower 60s south.
Long term...(thursday through tuesday)
issued at 407 am CDT Wednesday Jun 3 2015
The chance for thunderstorms will move into the area again Thursday
afternoon and night as low pressure aloft moves into the area.
Instability on the moderate side as the area is a bit deep into the
easterly low level flow. Shear also pretty weak as the middle and upper
level winds are not very strong. So...severe weather seems marginal
at best. Does at least look warm on Thursday with highs in the 70s
and overnight lows in the 60s.
Friday will see this wave exiting and more energy building up from
the south Friday night. Neither need very high chances for
thunderstorms at this time. Once again highs in the 70s and lows in
In the outer periods(saturday through tuesday)...weak ridging aloft
early in the period will be replaced by fairly light northwest flow
aloft as the northern stream digs a wave into Minnesota and
Wisconsin Sunday into Monday. As the wave begins to dig into the
northern plains a piece of energy will eject into the Central Plains
from the southwest United States low on Saturday afternoon and
night. This should bring the best chance for thunderstorms to the
during this time. After this northwest flow takes over and chances
for thunderstorms will be much lower Sunday into Tuesday. No real
cool air coming down with the northern stream wave...mainly just
enhanced mixing...so looking at highs in the upper 70s to middle 80s
each day...likely a little cooler than this on Saturday with
additional clouds and precipitation threat.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 655 am CDT Wednesday Jun 3 2015
Mesoscale convective vortex across eastern South Dakota will carry along a concentration
of showers and thunderstorms gradually into southwest Minnesota.
Models doing a very poor job with the entire scenario...and
biggest aviation issue not covered well is the mass of lower
clouds across northern South Dakota. With the persistent northerly
component filtering in behind the front settling southward...
these low clouds will move southward and create periods of MVFR
ceilings from later morning into the afternoon.