MD 1483 CONCERNING SEVERE POTENTIAL…WATCH LIKELY FOR PORTIONS OF WESTERN IOWA…EASTERN NEBRASKA…NORTH-CENTRAL AND NORTHEASTERN KANSAS…AND FAR NORTHWESTERN MISSOURI.
Mesoscale Discussion 1483 NWS Storm Prediction Center Norman OK 0231 PM CDT Thu Sep 20 2018 Areas affected...Portions of western Iowa...eastern Nebraska... north-central and northeastern Kansas...and far northwestern Missouri. Concerning...Severe potential...Watch likely Valid 201931Z - 202130Z Probability of Watch Issuance...80 percent SUMMARY...Thunderstorms capable of severe wind gusts will slowly increase along the front and move east throughout the afternoon/early evening. A Severe Thunderstorm Watch may be needed for at least portions of the area. DISCUSSION...A cold front trailing into southeastern Colorado from a deepening surface low near SUX will serve as the primary forcing mechanism for thunderstorm development this afternoon over this area. The strong frontal forcing, rather weak shear in the cloud-bearing layer, and veered low-level winds will support a rather quick evolution to a squall line mode, especially along the sharper portion of the front in Nebraska and far northern Kansas, as depicted in multiple convection-allowing model guidance through the morning. The consolidating cold front/narrow cold pool is expected to undercut the squall line, which will limit the overall severe threat. However, a deeply-mixed boundary layer with mixed-layer LCLs of 1600-2200 m and moderate mid-level lapse rates could support damaging wind gusts with the stronger embedded downdrafts that can remain close to the front. Farther west, thunderstorms have developed along and slightly behind the front in eastern Colorado and far western Kansas aided by the southern fringe of an elongated mid-level vorticity maximum. These storms may evolve more as cluster compared to the squall line to the northeast, but rather weak low-to-mid-level shear magnitudes should prevent any long-lived organization with these storms. However, severe wind gusts are possible given the moderate lapse rates and evaporation potential in the deeply-mixed boundary layer as they push east into west-central Kansas through the mid-late afternoon. Overall, a Severe Thunderstorm Watch may be needed for at least portions of the MCD area to cover the severe wind threat. ..Coniglio/Hart.. 09/20/2018 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...DMX...EAX...FSD...OAX...TOP...ICT...GID... LAT...LON 42339709 42659676 42979613 42949493 42869434 42589379 41889388 40449476 39749536 39199627 38509775 38479883 39559904 40329881 40609866 41089836 42339709
from SPC Mesoscale Discussions http://bit.ly/2NWhAGe
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