Tornadoes and NWS Storm Assessment Teams

Good evening everyone,

Add one more confirmed tornado to our July total. This was posted yesterday by my local forecast office.

And from their Public Information Statement

THE NATIONAL WEATHER SERVICE IN TAUNTON MA HAS CONFIRMED THAT
THREE WATERSPOUTS FORMED OFF THE COAST OF MANOMET IN PLYMOUTH
COUNTY AT 406 PM ON TUESDAY JULY 24 2012. THEY THEN RAPIDLY MOVED
ONSHORE...CAUSING MINOR DAMAGE AT WHITE HORSE BEACH BETWEEN
408 PM AND 409 PM...AND THEN DISSIPATED. THESE WERE PHOTOGRAPHED
WITH A TIME STAMP. TECHNICALLY...A WATERSPOUT MOVING ONSHORE AND
CAUSING DAMAGE IS CLASSIFIED AS A TORNADO.

Even with a couple more twisters in the month’s waning days this will still be the lowest twister total ever for July. The post however got me thinking about NWS storm assessment teams.

After severe weather hits a professional eye is needed to survey damage for the purpose of scientific research and insurance claims. Local meteorologists and emergency management officials are dispatched to areas where damaged has occurred to diagnose the cause. As you may guess, many pictures are taken, both from the ground and the air.

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With some damage, the cause is easier to figure (hail, flood). Other times it is less clear. A microburst is a concentrated downburst; it is a type of straight-line wind that originates high up in a thunderstorm but is often misdiagnosed as a tornado. I’d love to break down microbursts at a deeper level another time, but for now here is diagram.

So how do the assessment teams decide what caused that swath of damage? It’s the shape of the damaged area and the apparent direction of wind inside it.

  • A tornado will leave a thin path of damage with the winds traveling in all directions around the axis of rotation.
  • A microburst  will leave a broader, but not large, area of damage where all the wind is moving in the same direction. The direction of downed trees are often great clues in these cases.

If the team decides a tornado is the cause, the next step is assigning an EF rating. EF being the Enhanced Fujita Scale, a rating from 0-5 with zero being the weakest and five being the strongest. An EF 0 twister only has winds of between 65-85mph and can only cause light damage, while an EF 5 has winds of over 200 mph and can completely demolish large structures.
As a young meteorologist I look at these teams with envy. Being out in the field, seeing the damage first-hand and applying my knowledge. For now I guess this is a “maybe someday” thought. I found a wonderful page on the assessment process, prepared by Todd Shea at NWS office in La Crosse, Wisconsin.

Here’s the link here:  http://www.crh.noaa.gov/arx/?n=stormdamage

Enjoy everyone!

~Wildcard

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