Friday, June 12, 2015

Why was there no tornado warning?

I've been getting personal messages  on the question...Why wasn't there a tornado warning on the tornado that touched down Tuesday in the village of Scotia,  20 miles northwest of Albany?

The simple answer is the NWS didn't know it was there.  But the bigger question is why didn't they know? The answer to that question is far more complex than you might imagine.

The Plains, Gulf States, and Midwest see a lot of tornadoes every year. The Northeast sees far less...but even at that we end up on average with around two dozen tornadoes every year.

The tornadoes out west typically form from a Supercell Thunderstorm. On my blog I've done several post on Thunderstorms and are two of them

One is about Supercells the other is about  Tornadoes .

I won't go into detail on Supercell tornadoes, you can read about that on the blog. But I will say, supercell tornadoes occur from thunderstorms with deep rotation in the storm; rotation meteorologists refer to as a mesocyclone.  The tornado descends out of that mesocyclone, and you can see that rotation on the radar.  The mesocyclone is easily seen on radar and nearly always has a tornado warning issued in association with it.  These are the type of tornadoes that occurred during the Alabama outbreak of 2011 , the Joplin EF-5 tornado, and the Picher, OK EF-4 of 2008.   The National Weather Service will always issue warnings on these.

While the Northeast does see Supercells and the rare supercell tornado....the typical tornado in the Northeast is a different type of storm.

The tornado that formed Tuesday near Scotia, was what is called a Squall line tornado. Squall line tornadoes are called QLCS (Quasi Linear Convective System) Tornadoes in the meteorological world. But they can also be called spin up tornadoes or bookend vortices.  

QLCS tornadoes are typically weaker than their supercell counterparts. The vast majority are EF-0 or EF-1...but a few have been as strong as EF-2 or even EF-3.  A squall line tornado is very hard to see on radar. There are a few reasons for this.

One) they are very short lived many times lasting only a few minutes. QLCS tornadoes form on the leading edge of squall line. along the squall line there is a lot going on and it's hard to keep track of it all. If it produces a V notch it is very hard to see.  They also form from the ground up not from the thunderstorm down. This often means the rotation doesn't reach the cloud, until after the tornado has formed.  

Two) current dopplar weather radar  has several limitations....It takes it five minutes to make a complete turn cycle. Many times the tornado can be gone when the radar comes around to see it.  

So even if the tornado hook shows up on radar on one scan. It would most likely be gone on the next scan. So there would be no time in which to issue a warning.   Another thing that makes squall line tornadoes hard to see on the angle of the radar beam..... the beam shoots into the sky at a 0.5-degree angle. ..we also have to take the curvature of the earth into account.  So the radar beam is  several thousand feet in the air at a moderate distance . It could very well be shooting over the top of the tornado.

 The tornado that formed last night in Northern Ontario County, near eastern Farmington close to Canandaigua, NY. was another example of a squall line tornado. NWS Buffalo issued the warming for the storm at 9:46 PM....which was just about the same time the tornado formed. The tornado was rated EF-0 and was only on the ground for a half-mile. So there was no time for anyone to really react to the warning in the first place.

You may be surprised to know during severe weather all media meteorologists as well as National Weather Service Meteorologists are in a closed, private chat session online discussing the situation that is unfolding.

Such was the case with last July's Madison County Smithfield, NY tornado, which killed four people.

There was a discrete mesocyclone heading for Syracuse, NY that had  the attention of meteorologist and the National Weather Service. The storm had a lot of very strong rotation with it. The Weather service in Binghamton did end up issuing a tornado warning on the storm near Syracuse at 5:39 p.m. The good news for Syracuse was the storm never spawned a tornado.

 Behind the mesocyclone there was an intense squall line...So while the mesocyclone never produced a tornado, the squall line did.  The tornado formed just below a 1,400-foot ridge in central Madison County about 7:02 p.m.  The tornado hit Smithfield before it even showed up on radar.   In Smithfield it killed  a mother, her 4-month-old baby and an older female relative.  It also destroyed a nearby house where  one man and his dog died.  The tornado moved away at 50 mph, heading down the north side of the ridge and dissipated at 7:06 p.m.. in less than  four minutes it came and went.

The day of the Smithfield tornado was very active.  The line ended up forming five tornadoes.

False alarms:

Many of the tornado warnings issued by the NWS never had a tornado in the first place. Roughly 75% of the warnings issued are in fact a false alarm. Because of this many times people will ignore tornado warnings when they are issued. If the NWS issued a warning for every possible spin up along a squall line the false alarm rate would be much higher.

This can create a dilemma for the NWS on how to warn on these scenarios. Issue a tornado warning after seeing possible rotation that could be a QLCS tornado. Don't issue a warning at all. Or just allow the severe thunderstorm warning to handle the brief spin up.
My view is don't issue the warning for a possible squall line tornado at all. This is why everyone should take severe thunderstorm warnings seriously.  Severe thunderstorms can and do produce tornadoes....that squall line heading your way, could form a brief tornado, with or without a warning.

The nature of QLCS tornadoes in the Northeast, is what makes them so extremely dangerous. Most of the time no one knows they're there until it's come and gone. They are difficult if not impossible to warn for......The entire line is capable of producing damaging winds with or without a tornado..  

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