South Dakota Mesoscale Discussion

Areas affected…south central ND…central SD

Concerning…Heavy rainfall…Flash flooding possible

Valid 091630Z – 092230Z

Summary…Showers and thunderstorms will continue to develop
across portions of central SD into south-central ND through the
next couple of hours. Storms will be slow to propagate initially
leading to the potential for flash flooding across this region
over the next several hours.

Discussion…The northern tier of the mid-level ridge will become
suppressed as impulses move from the approaching trough in the
west across Montana into the Dakotas through the day into the
overnight. Aloft, divergence will increase as the upper level jet
to the east strengthens with this region becoming positioned under
the right entrance region. This combined with plenty of mid-level
vorticity will promote strong synoptic scale lift. We are already
observing evidence of this from radar with moderate to heavy rain
slowly tracking north and east. At the surface, a stationary
boundary will help enhance lift as the 850mb southerly winds
supplying moisture and instability moved up and over this front.

Precipitable water values are over 1.5 inches with instability
already between 1000-2000 J/kg MUCAPE across this region. Though
there is some concern that cloud cover and early morning
convection could hinder destabilization, we are already seeing
surface based CAPE values increasing. In addition, with the
aforementioned synoptic scale features in place, feel there is a
strong signal for convection leading to efficient/heavy rain
rates.

The potential for heavy rain will only increase as we move through
the afternoon toward the evening hours as divergence, mid-level
vorticity, increasing 850mb southerly flow and surface/mesoscale
features become aligned. This is supported by hi-res models with
much of the activity eventually riding southeast along the clearly
defined instability/theta-E gradient in place. Thus expect the
heaviest rain and training due to slower storm motions to impact
north-central SD and south-central ND within the next couple
hours. As mentioned, this activity should start to sink southeast
into eastern SD by mid/late afternoon. Rain rates will likely
exceed 1.5 inches with 3 hourly precipitation totals 2-4 inches
in some locations. With pockets of FFG below these values, feel
flash flooding is possible across this region.

Pagano

…Please see www.wpc.ncep.noaa.gov for graphic product…

ATTN…WFO…ABR…BIS…FSD…UNR…

ATTN…RFC…MBRFC…

LAT…LON 46550002 46429896 45469805 44779745 43969779
43609882 43860096 45200230 45940166

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