Mesoscale Discussion 1543
NWS Storm Prediction Center Norman OK
0235 PM CDT Mon Aug 21 2017
Areas affected...Northeast NE...Far southeast SD...Northwest into
central IA...Southwest MN
Concerning...Severe Thunderstorm Watch 460...
Valid 211935Z - 212100Z
The severe weather threat for Severe Thunderstorm Watch 460
continues.
SUMMARY...The threat for locally damaging wind and sporadic hail
continues with the long-lived MCS. There is some uncertainty
regarding the southeastward extent of the severe threat, but new
watch issuance downstream is possible.
DISCUSSION...At 1930Z, a compact, long-lived MCS is moving into
northeast NE/northwest IA. Sporadic instances of large hail and
strong wind gusts have been noted over the last 1-2 hours with this
system across southeast SD. The strongest part of the system
continues to be with an embedded supercell structure at the apex of
the bowing segment, with weaker development further southwest just
behind the trailing outflow boundary. While the system is small, it
is well-organized, with a relatively strong cold pool and some
indications of a strong pressure rise-fall couplet. Some damaging
wind threat will continue with this system, while local instances of
hail are also possible given steep midlevel lapse rates feeding in
from the west.
While the system is likely to persist for much of the afternoon as
it moves southeastward, there is some uncertainty regarding the
severe threat downstream, given relatively weak heating in the wake
of earlier convection and substantial remaining SBCINH. If the
system maintains its intensity as it approaches the edge of the WW
460, downstream watch issuance is possible into a portion of central
Iowa.
..Dean.. 08/21/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MPX...DMX...FSD...OAX...GID...LBF...
LAT...LON 42049891 42909684 44039629 44139532 43539376 43019339
42239345 41639384 41609615 41669795 41679937 42049891
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