Derecho — Weather Wednesday

Julyderecho
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 – Killer Heat

NOAA Archives
NOAA Archives

The July issue of Chicago Magazine serves as the inspiration for today’s post on killer heat. It features a recap, told in the words of residents, first responders, morgue workers and politicians of the July 1995 heatwave in the City of Chicago…twenty years ago next week. I recommend it.

Heat remains consistently the deadliest natural disaster in most years in the United States. The National Weather Service estimates that about 175 people die of heat related causes during an average year. Some years are much worse. The official total of dead attributed to the 1995 event in Chicago stands at 739. Officials argued about which deaths belonged in the count at the time and continue to do so today, but in any event the extent of the disaster cannot be denied.

On Wednesday, July 12, 1995, the temperature in Chicago reached 95-degrees. Certainly not uncommon. But on Thursday the 13th, the high was 104 at O’Hare Airport and 106 at the more urban Midway Airport. To compound the stress, the dewpoint at times exceeded 80-degrees which is rare. That would make the heat index between 120 and 130-degrees.

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Chicago Tribune

By Friday, July 14, with a high of 102, paramedics and police officers knew there was a major problem. The number of fatalities rose to the point that the system was overwhelmed. Refrigerated trucks were brought to the morgue and mortuary students worked non-stop for two days assisting the morgue staff in handling the bodies of victims.

 

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Chicago Tribune

The urban heat island effect was in full operation. Buildings and pavement held the heat at night, especially in the humid air so there was no relief. Many of the victims were elderly, young and those with existing medical issues. The situation was especially dire in poorer neighborhoods where residents either had no fans or air conditioners or were reluctant to use them given the cost of electricity. In addition, some victims were fearful for their safety and kept windows closed and locked. One of the city’s major hospitals lacked air conditioning in most of the building even in 1995! Surgical staffs were rotated frequently.

Since the effects of extreme heat tend to be cumulative, people continued to succumb for days after the heat began to subside on Saturday when the high was “only” 98.

heat_1The Chicago Heatwave of 1995 was a well-documented event, but similar heatwaves are common. Just this past week much of Western Europe had unusually high temperatures and in June perhaps as many as 1,500 people died of the heat in Pakistan. In May of 2015, 2,500 people died in a heatwave in India.

 

The National Weather Service has a number of safety tips, including:
Avoid the Heat. Stay indoors and in air conditioning as much as possible
Check on neighbors and the elderly.
Wear loose fitting clothing. Light colors reflect heat and sun.
Drink plenty of water and natural juices. The body loses water faster than it can absorb it. Avoid alcohol and caffeine.
Avoid large meals. Eat smaller portions and more frequently.
NEVER leave children or pets in a vehicle even for a few minutes.

In addition, the weather service has a heatwave brochure available for download.

Weather Wednesday – When the Smoke Gets in your Skies

-- NOAA
— NOAA

For the past several days the media has been showing images of a smoke plume reaching from wildfires in Saskatchewan  across the Midwest and farther south.   From the ground the smoke appears as a haze high in the sky and may filter the sun.   Sunrises and sunsets in the areas where there is smoke in the atmosphere have been more colorful than usual.

While such events occur fairly frequently, this one has garnered additional attention because of the vast area that is reporting at least some smoke.  It is expected the area will shift to the east as the weather pattern changes over the holiday weekend.

IMG_1097Here’s what the sky looked like in central Illinois at about 11AM on Wednesday, July 1, 2015.  The darker parts of the image are clouds, put the sun is seen filtered in part by the smokey haze.

At the current time most of the smoke is high in the atmosphere and is not likely to be able to be smelled nor is it a particular threat to those with breathing difficulties.   However, the situation is different in parts of Alaska where a Dense Smoke Advisory has been issued near some wildfires. There people have been cautioned not only about limited visibility but the possibility of health impacts.

Nearly all of the wildfires have been caused by lightning.

As we approach the July 4th holiday, please keep those fireworks under control and don’t contribute to any new wildfires.