Monday, July 13, 2015

Big Severe Storm Outbreak Skirts Edges Of Heat Wave Today

Areas in red in this map have the highest chance
 of seeing very severe thunderstorms and maybe
 a few tornadoes today.  
Tornadoes and severe thunderstorms packing destructive winds, hail, lightning nad flooding rains raked parts of the Dakotas, Minnesota and Wisconsin yesterday and last night.

The exciting batch of weather if anything is going to intensify as the weather system causing the storms slides southeast through the Great Lakes, Ohio Valley and into the Southeast.

This is a classic so-called "Ring of Fire" severe weather outbreak.

This refers to a common mid-summer weather setup in which a hot high pressure system sets up, in this case over the southern Plains. Around the northern periphery of these heat ridges, a ring of thunderstorms often sets up.

That's the "Ring of Fire" I talked about.

Sometimes on the northern or northereastern most part of the Ring of Fire, a particularly nasty batch of storms develops. Often, this becomes a derecho that races east or southeast into the United States.

I don't know if this case will result in a derecho, but as of early Monday morning, it looks like the severe storms were maybe organizing into one in Wisconsin. If this develops it wil race southeastward into Illinois,  Indiana and a good chunk of the Ohio River Valley.

A should step back and define a derecho. The official definition is that it's an intense line of storms that covers a distance of at least 250 miles, and inclues wind gusts of at least 58 mph along most of its lentgth, and has several, well separated gusts of at least 75 mph.

It's not unheard of to get reports of winds gusting to 110 or 120 mph in parts of some derechos.

A lot of us weather geeks and bloggers are reluctant to use the term "derecho" in advance of one because when you use the "D" word, it becomes the subject of a lot of media hype. After all, derechos are worse, more widespread and cause more damage than a typical, usually smaller line of severe summer storms.
Damage from a 2009 derecho in Carbondale, Ill.  

But in this case, it looks like there well could be an official derecho today, perhaps already beginning to be underway as of early Monday morning. We'll have to see it it is an official derecho after all is said and done tonight.

By the way, a derecho isn't the only dangerous risk today in the storm zone.

Supercell thunderstorms might get going ahead of the main band, or bands of thunderstorms. These can spin up tornadoes, and the region I've outline for today's severe weather could get a few tornadoes.

One or two of these tornadoes might end up being quite strong, says NOAA's Storm Prediction Center.    

Flash flooding is also possible in some of these areas, because the torrential rain associated with the storms will move over areas that have already gotten LOTS of rain this month.

Needless to say, watch out if a derecho gets going. Derechos are very dangerous, because they cover a wide area and often move over heavily populated areas.

One of the most famous recent derechos, in June, 2012 moved from the Great Lakes and Ohio Valley areas into the Mid-Atlantic states. It killed 22 people and cut power to at least 5 million people.

Some derechos can last a very long time. One of the worst was actually a series of derechos in July 1995 that extended from eastern Montana all the way to the New England coast.

One of these derechos crashed through Ontario and then into New York's Adirondacks late one hot night. Winds of 100 mph or more killed at least 5 Adirondack campers, and many more had to be rescued by helicopter as thousands or perhaps even millions of trees toppled in the extreme winds.

That derecho continued on into the Albany Capital District, southern Vermont and other parts of New England, causing widespread damage.

So you see, these things can be nasty. Very nasty.

If you're anywhere in a broad region between Wisconsin and the Carolinas today through tomorrow, keep  an eye to the sky and get indoors in a sturdy building at the first sign of storms or if you get a severe thunderstorm warning.

In many cases, these will be much more than the usual garden variety thunderstorms.

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