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NWS Warns of Severe Weather and Possible ‘Derecho’

The National Weather Service (NWS) is forecasting a widespread severe weather outbreak from the Great Lakes southeastward into the Mid-Atlantic states on Wednesday. The severe threat includes the potential for storms to form an organized line packing damaging winds, heavy rainfall and large hail. Specifically, NWS meteorologists are highlighting the threat for a derecho (pronounced de-Ray-cho) event, which is a widespread, long-lived swath of damaging winds associated with swift-moving thunderstorms.

According to the Storm Prediction Center in Norman, Okla., an event qualifies as a derecho if the wind damage extends more than 240 miles and includes wind gusts of at least 58 mph for most of its path. 

Severe thunderstorm outlook for Wednesday, June 12.
Credit: NOAA SPC.

Major cities at risk include Chicago, Columbus, Detroit, Dayton, Indianapolis, Milwaukee, and Cleveland. The severe storms may spread southeastward out of the Midwest, and into the Mid-Atlantic Wednesday into Thursday. All told, nearly a dozen states and more than 50 million people are in areas considered to be under heightened risk. Severe thunderstorms are likely again Thursday in the Mid-Atlantic, from Richmond to New York City, as the storm system moves eastward, and there is a heightened risk of tornadoes in the Washington D.C. area on Thursday.

"It's a pretty high threat," Bill Bunting, operations chief of the Storm Prediction Center, told the Associated Press. "We don't want to scare people, but we want them to be aware."

In addition to the threat of widespread damaging winds, the storms also may cause flash flooding, since they will affect areas that have recently received above-average rainfall. 

"These can be large systems, sometimes almost the size of a tropical cyclone," said Ken Pryor, a research meteorologist at the Center for Satellite Applications Research at the National Oceanic and Atmospheric Administration in College Park, Md. Pryor said these events feature "widespread damaging winds that can rival that of a strong tropical storm or weak category 1 hurricane." For example, a derecho that tracked from Iowa to Maryland and Virginia in July 2011, had winds of greater than 100 mph, Pryor said.

Satellite loop of the June 29, 2012 derecho that tracked from near Chicago to east of Washington, D.C.

Derechos are relatively frequent events in the Midwest, where they occur about once a year, and in the Mid-Atlantic states, where they occur about once every five years, Pryor said. In June 2012, an unusually destructive derecho, touched off by a record warm and humid airmass, formed over eastern Iowa and traveled more than 700 miles in one night, knocking out power to more than 4 million customers from southern Indiana to Maryland. That storm system produced winds of greater than 90 mph and led to at least 24 deaths in seven states.

Pryor said meteorological data shows “very similar atmospheric forcing conditions” on Wednesday to those that existed before the June 2012 event, particularly from southern Illinois to the central Appalachians and the Carolinas.

Wednesday’s storms are likely to be set off by a jet stream disturbance riding along the outer fringes of a dome of high pressure anchored across the West and South Central states. At the surface lies a warm front that is draped across the Midwest, and a developing area of low pressure in the Missouri River Valley, which will act as a focusing mechanism for the storms. 

The high pressure area is contributing to record heat from Nevada to Illinois. Denver, Colo., for example, had its earliest 100-degree day on record on Tuesday. This warm air is creating an unstable air mass that will allow thunderstorms to intensify as they propagate southeastward from Wisconsin, Iowa, and Illinois on Wednesday afternoon.

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By Eric Peterson (Front Royal, VA 22630)
on June 13th, 2013

No derecho.  As noted at Capital Weather Gang (where Andrew came from), the complex is moving through at the least energetic time of day.  The storms later today may be severe but they will not be in a organized line (hit or miss instead).

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By hank
on June 13th, 2013

I’m constantly wondering if the name of this site should be changed to “Weather Central”. What do you think?


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By Eric Peterson (Front Royal, VA 22630)
on June 13th, 2013

hank,  you are absolutely right.  The media and sites like this have purposely chosen to blur the line between global warming and weather, so we hear almost nothing but scary stories and forecasts whether they turn out true or not.  To their credit they present good news weather stories here like the drought area shrinking.  But that mostly proves that those are indeed weather stories, not climate (or “climate change”).

As it turned out today, no derecho, just hit or miss storms.  The one from my county (Warren) through Leesburg into Monty county MD was quite severe.  Not historic or unusual.

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By Andrew
on June 13th, 2013

Hank and Eric - Thanks for your comments. We have not chosen to blur the line between global warming and weather on this site, but rather we made a decision to cover some extreme weather events and make clear what the science says about their potential connections to climate change. We’re very upfront in saying that there are some events about which the science is unclear, such as tornadoes, for example.

A scientific argument could be made that climate change is increasingly blurring the line between weather and climate change, not the news media, given that all weather events now occur in a warmer and more humid background climate. The media, including us, are only following the science on this, nothing more.

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By Eric Peterson (Front Royal, VA 22630)
on June 14th, 2013

Thanks Andrew for the explanation.  I don’t believe the scientific community is always independent of the media as we see with some “science by press release”.

All weather events occur in a background of weather, GHG levels is only one input (and not the most important).  All CO2 does is raise the global average a bit over time but weather swings the global average temperature up or down in a week or two what it takes CO2 a decade to do.

Humidity is much more of weather than a climate phenomenon than temperature.  The strong tornadoes in the plains are a great example requiring both humidity and dryness as two of their essential ingredients (along with warmth and a decent jet).  The science is very clear about how those form, and evaluating global warming connections is an exercise in media relations more than it is science.

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