Derecho — Weather Wednesday

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July 13, 2015 derecho radar image from NOAA.

Early this week, on July 13, a possible derecho, or at least what the National Weather Service is currently calling “a Derecho-like event,” raced across the middle of the country. It began in Minnesota and swept mostly southward through Wisconsin, Illinois, parts of Indiana and into Kentucky.

The Weather Service describes a derecho as “a widespread, long-lived storm. Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines or quasi-linear convective systems.”

The “bow echo” refers to the characteristic appearance of a linear storm on weather radar when that storm bows out due to high wind. Storms represented by bow echoes are not always derechos unless they last for a long time which is rarely the case. In fact, large derechos are relatively unusual. Generally there are only one or two a year in most of the country.

The Weather Service has an extensive derecho page.

Weather Underground
Weather Underground

Derechos can be extremely damaging. By definition a derecho must travel 240 miles and include wind gusts of at least 58mph along much of its length and several gusts of over 75mph. Many are much stronger. A derecho that crossed Illinois from northwest to southeast in the late 1990’s included winds measured at over 100mph at the Clinton nuclear power plant and caused extensive damage to a marina at the associated cooling lake.

Effects can be long lasting. On July 4th and 5th in 1999 a derecho crossed the Boundary Waters Canoe area in northern Minnesota/southern Ontario. It devastated a forest there. Wildfires in more recent years have been fueled by the debris from that storm.

Because of their length and the intensity of the straight line winds, derechos can be an extremely costly event. Casualties are rare, but do occur, usually caused by falling trees or other debris and occasionally by watercraft caught by the rapidly moving storms.

Weather Wednesday – El Nino and the Texas Floods

KHOU via USA Today
KHOU via USA Today

What caused the recent devastating and deadly flooding in Texas, Oklahoma and other states? One thought, advanced by Accuweather and others, is that the developing El Nino played a role. As we’ve written before, an El Nino is warmer than expected waters in the Pacific Ocean. El Nino events result in a split jet stream and it the southern stream likely contributed to the flooding in the South. Typically, heavier than normal rains occur in Spring, Autumn and Winter of El Nino years in a swath from California into the Mid-South.

EPA
EPA

Historically, even weak and/or developing El Ninos can cause the extreme precipitation witnessed in May. California largely missed out although the area around San Diego picked up record rainfall. In past El Nino events California received most of its precipitation during winter months. It remains to be seen if the current event will last that long.

In the meantime drought conditions have been greatly lessened in Texas, at least in the short term. Of course that came with a terrible price…dozens of deaths and hundreds of millions of dollars in damage. The toll continues to rise and many rivers remain in flood.
EDEN Flood Resources:

Agriculture

Flood insurance

Misc collected resources

eXtension Flood Page

Weather Wednesday — Hurricane Season Outlook

Tropical Storm Ana earlier this month aside, June 1st marks the beginning of the “official” Atlantic Hurricane season. So what can we expect this year? Exact predictions are always iffy, but noted expert Dr. William Gray and his colleague Philip Klotzbach, both of Colorado State University, predict 7 named storms, three hurricanes and one major hurricane. If true, this would be one of the quietest hurricane seasons in the last 60-years. The long term average is for 12 named storms, six hurricanes and two major hurricanes. Some recent years have seen in excess of 20 named storms.

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NOAA

Why the smaller numbers? One factor is the development of a strong El Nino in the equatorial Pacific Ocean. Historically, El Nino years have fewer hurricanes along with other effects. The Weather Channel has created a nice page and video explaining this.

It is extremely important to note, however, that it only takes one major landfalling hurricane to cause vast damage and many casualties. Just because the long range hurricane forecast seems to be encouraging, we’re not out of the woods.

Hurricane-Sandy-stormsurgediagramIn preparation for the 2015 hurricane season, the National Hurricane Center is unveiling a new system of communicating storm surge threats and vulnerabilities. As has been seen over and over, some of the most devastating damage from hurricanes is not always from strong winds but from storm surge, the wall of water that is pushed out in advance of the center of the hurricane.

20121106-hurricane-sandy-new-jersey-shore.jpg.662x0_q100_crop-scale Hurricane Sandy is one of the more recent demonstrations of this mighty force.

This week, May 24-30, is national Hurricane Preparedness Week.  For those of you who have a role educating others about hurricanes here’s a link to FEMA’s toolkit.   And here is material from the National Hurricane Center/NOAA.

 

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National Dam Safety Awareness Day is May 31st. That date is the anniversary of the failure of the South Fork Dam which resulted in the infamous Johnstown (PA) flood. More than 2,200 lives were lost in what is considered the worst dam failure in the history of the United States according to FEMA.

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Missouri Institute of Science and Technology

The National Dam Safety Program is led by FEMA and a partnership of states, federal agencies and other stakeholders. Dams are part of an aging infrastructure and continued attention is vital in averting future catastrophic failures.