[EAS] 9-1-1 Outages From Derecho/Windstorm

[Mike McCarthy]

Deracho's are a specific type of long track storm cluster phenomena. 
They usually are a meso-convective (multi-cell) system involving a 
mesocyclone supporting the long track regenerating storm life cycle. It 
easily possible the event you describe could have a been bow echo or 
LEWP (Line Echo Wave Pattern). Deracho's are not as common as bow echoes 
or a LEWP in a squall line.  In those instances, jet-stream level winds 
can be pulled down to the ground by the parent storm and create a bulge 
in the storm line.  The wind damage potential can be equal to that of a 
Deracho.  But the scientific physics behind the effect are different.

 From the NWS: Line Echo Wave Pattern. A bulge in a thunderstorm line 
producing a wave-shaped "kink" in the line. The potential for strong 
outflow and damaging straight-line winds increases near the bulge, which 
often resembles a bow echo. Severe weather potential also is increased 
with storms near the crest of a LEWP.  (END)

In your example, it's entirely possible that either occurred due to 
minimal resistance of wind over the water upwind from the island. The 
result being the more intense damage.

That's not to say LEWP's can occur in Deracho's when they start to 
gather their meso level energy and characteristics. But once sustaining, 
Deracho's more often will involve smaller sized bow echos than longer 
length LEWP's.

MM

On 1/18/2013 11:13 PM, Tim Stoffel wrote:
> Mike,
>      Thank you for confirming my suspicions. I have been through two derecho events while I lived in Rochester, NY. One of these wiped an island in the 1,000 islands area off the map. In the 12 years I have lived in Nevada, I cannot recall a storm that even approached the intensity of those two storms.
>
> Tim Stoffel