Areas affected…Portions of eastern SD…far northeastern
NE…west-central/southwestern MN…and northwestern IA
Concerning…Severe potential…Watch likely
Valid 172212Z – 180015Z
Probability of Watch Issuance…95 percent
SUMMARY…The severe threat will increase this evening, with
damaging winds and large hail possible. Isolated tornadoes may also
occur. Watch issuance will very likely be needed within the next
couple of hours.
DISCUSSION…A broken line of storms has developed along a surface
cold front this afternoon extending northeast-southwest across SD.
22Z surface analysis also shows a weak surface low centered along
the NE/SD border, with a diffuse warm front extending eastward from
this low across southeastern SD and far northeastern NE. The
stronger mid-level flow associated with a large-scale upper trough
appears to be lagging west of the surface cold front and associated
convection, which has tended to limit the intensity of these storms
so far this afternoon. Still, at least isolated damaging winds
should continue to be a concern as this activity spreads eastward
into eastern SD and vicinity this evening. There also appears to be
some potential for discrete storm development along the warm front
in southeastern SD and far northeastern NE based on latest
short-term guidance and recent radar/visible satellite trends.
Effective bulk shear of 35-40 kt and moderate to strong instability
would initially promote supercell structures across this region,
with both a large hail and damaging wind threat. Isolated tornadoes
may also be a concern if a couple discrete supercells can develop
along/near the warm front given a very moist low-level airmass, and
backed southeasterly low-level winds supporting generally 150-250
m2/s2 of effective SRH through early evening. Watch issuance will
very likely be needed within the next couple of hours as storms
continue moving eastward.
..Gleason/Guyer.. 08/17/2019
…Please see www.spc.noaa.gov for graphic product…
ATTN…WFO…MPX…FSD…OAX…ABR…LBF…
LAT…LON 43019948 44569825 45719715 45709572 45069504 44199490
43499506 42819555 42449651 42429750 42599860 43019948