MD 1581 CONCERNING TORNADO WATCH 468… FOR UPPER TX COAST…FAR SOUTHWEST LA
Mesoscale Discussion 1581
NWS Storm Prediction Center Norman OK
0937 PM CDT Sat Aug 26 2017
Areas affected...Upper TX Coast...Far Southwest LA
Concerning...Tornado Watch 468...
Valid 270237Z - 270430Z
The severe weather threat for Tornado Watch 468 continues.
SUMMARY...Enhanced tornado threat from League City to Brenham
appears to be waning. Even so, the threat for tornadoes will persist
throughout the night, particularly if another convective band
develops.
DISCUSSION...Convective band associated with Tropical Storm Harvey
has intensified over the past two hours with recent GOES-16 clean IR
window sampling cloud tops around -80 deg C and recent radar imagery
sampling 40 dBZ on the 9km CAPPI. This intensification occurred
within an area of greater daytime heating, resulting in slightly
stronger instability and low-level lapse rates. Easterly motion of
this band has slowed a bit compared to earlier this evening but
gradual eastward progress is still expected over the next several
hour. Cells within this band will continue to move northward or
north-northeastward at around 20-30 kt.
The gradual eastward progression of this band will take it into an
environment characterized by less surface convergence and weaker
low-level (i.e. 850 mb) flow, which results in less storm-relative
helicity. Consequently, the tornado threat posed by this band
appears to be lessening with time. However, additional banding is
possible and the tornado threat will persist throughout the night
across much of the upper TX coast. More cellular development farther
east could also pose an isolated and brief tornado threat.
..Mosier.. 08/27/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LCH...HGX...CRP...EWX...
LAT...LON 29319663 30259638 30949471 31019386 30359344 29669326
29479439 28899531 28559633 29319663
from SPC Mesoscale Discussions http://bit.ly/2bx8CMa
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