Areas affected…central/eastern SD
Concerning…Heavy rainfall…Flash flooding possible
Valid 092230Z – 100430Z
Summary…Convection continues to move across South Dakota this
afternoon with the expectations that this activity will shift
southeast through the evening. Hourly rain rates could exceed 2
inches associated with the strongest storms moving through the
central portion of the state. Flash flooding is possible as some
of these convective cells may train and merge over the next couple
Discussion…An upper level jet streak of 100 knots will slide
east positioning the right entrance region across this area. This
will only act to maintain and possibly even enhance the lift over
the next couple of hours. Additionally, mid-level shortwave
energy moving from WY into SD will be another lifting mechanism.
Strong southerly 850mb flow will move atop a surface boundary
draped from northwest SD to south-central SD. This flow will
increase through the evening hours which may help to promote a
complex formation. The evolution of this system is hard to
discern, but regardless the lift is present.
In terms of other key ingredients, precipitable water values above
1.75 inches combined with MUCAPE of 1000-2000 J/kg will ensure
that convection continues over the next couple of hours with
efficient rain rates overall. Radar indicated rain rates
currently are around 1.5-2 inches associated with the heaviest
convection. Expect this trend to continue, though some estimates
may be hail contaminated, which was taken into consideration.
The storm motion continues to show 15-25 knots to the south and
east, though cell mergers and the potential for training farther
east is noted with the corfidi vectors becoming better aligned
with the mean flow. There continues to be elevated convection
that may show signs of training, though the storm totals overall
should be less than that observed along the swath of more
discrete/heavier cells. Therefore, the main potential for flash
flooding will likely coincide ahead/along the better instability
and moisture gradient across south-central/southeastern SD.
The limiting factor is with respect to the quick storm motion and
the FFG lowering to the east. Regardless, with the aforementioned
ingredients, still feel there is a flash flood threat in place
through the evening hours.
…Please see www.wpc.ncep.noaa.gov for graphic product…
LAT…LON 45469826 45259662 43579646 42789666 42709835