Weather Quiz

1. Which month is the busiest of the hurricane season?

A. July

B. September

C. November

Please submit your answers as a comment below.  Come back next week to find out if you were correct and why.

Destructive and Rare: DC Derecho Two Years Later

The last several years have certainly featured some unique weather in parts of the country unaccustomed to seeing it.  From extreme and prolonged drought across much of the western and south central United States to more frequent and more destructive rounds of severe weather – whether tornadoes, high winds or large hail.  Before two years ago, the term “derecho” was also outside the lexicon of weather terminology for those living on the East Coast.

Most Mid-Atlantic residents will remember two major weather events that occurred two years ago this week.  Not only was June 29, 2012, the hottest June day on record in the Nation’s Capital with a daily and monthly record high of 104 degrees but it was also the day of an infamous “derecho.”  In meteorology, a “derecho” is a long lasting line of fast moving thunderstorms that features damaging winds.  Quite often the winds exceed severe criteria gusting in excess of 58 mph.

The combination of record heat and atmospheric instability made conditions ideal two years ago today for the “derecho” to not only form but remain intense as it traveled hundreds of miles from the Ohio Valley to the Mid-Atlantic Coast.  People could track the line of storms on radar as it moved rapidly eastward during the afternoon and early evening.

Shortly after dark when the “derecho” moved through the Mid-Atlantic Region, the National Weather Service recorded many severe wind gusts between 60 and 80 mph.  That resulted in power outages to millions of people as well as several fatalities – largely the result of falling trees – around the Nation’s Capital.  Since so many trees and power lines were knocked down by the “derecho,” it took power crews almost a week to restore power to the majority of customers in the Mid-Atlantic. 

Making matters worse was the fact that June 29, 2012, was only the second day of an 11 day stretch with high temperatures of at least 95 degrees in the Nation’s Capital.  In fact, between June 28 and July 8, 2012, there were 5 days that reached 100 degrees or hotter in Washington, D.C.  The extreme heat combined with the extended power outages created a great deal of hardship for residents of Maryland, Virginia and the District of Columbia. 

Fortunately, “derecho’s” are exceptionally rare in the Mid-Atlantic Region and the majority of weak or damaged trees were either knocked down during the “derecho” or cut down in the process of restoring power.  So by the time “Superstorm” Sandy impacted the Mid-Atlantic Region four months later, there were significantly fewer power outages due to improved infrastructure.

Improved weather satellite and computer modeling technology has allowed for better weather forecasts.  This allows scientists to issue more timely weather watches and warnings for a wide range of weather events ranging from severe weather to tropical storms and hurricanes.  Fortunately, no record setting heat or severe weather is expected in the Mid-Atlantic Region this week.

June Severe Weather

Washington, D.C. storm

Due to its unique geography, the United States averages more tornadoes in a given year than any other country in the world with annual totals of over 1,000 common.  Tornadoes have been recorded in all 50 states, but are most common in a region of the central United States from Texas northward through South Dakota; known widely as “Tornado Alley.”

Traditionally, thunderstorms form from large, long lasting thunderstorms known as “supercells” that travel long distances.  Ideal circumstances for tornado outbreaks occur commonly during the spring when warm, humid air from the southeastern United States clashes with cooler, drier air from the north and western regions of the country.  Consequently, the U.S. averages more tornadoes during the month of May with almost 400 than in any other month of the year according to statistics from the National Climatic Data Center.

As the jet stream – a river of air that guides storm track – assumes its typical summertime position farther north the cool, dry air retreats into Canada.  This allows warm, humid weather to envelop most of the central and eastern United States.  Therefore, the northern Great Plains states – Iowa and Nebraska to Minnesota and Wisconsin typically see the majority of their severe weather from June through August according to scientists at the Storm Prediction Center.  A thunderstorm is considered “severe” if it contains any of the following: 1) hail at least 1” in diameter; 2) a wind gusts of at least 58 mph within a thunderstorm or 3) the presence of a tornado.

Just last week there was a major severe weather outbreak in the Upper Midwest with more than 100 tornadoes reported in a four-day stretch from June 16 through June 19 with the highest concentration in Nebraska and the Dakotas east through Iowa, Minnesota and Wisconsin.  Tragically, this tornado outbreak proved to be both damaging and deadly.  So that heightens the importance of the public to remain vigilant and take safety precautions when severe weather watches and warnings are issued.  That’s true across the United States wherever extreme weather may occur.

June Hurricanes

Although hurricane season began June 1, tropical storms are relatively rare during the month of June as the peak of the season doesn’t come until early September.  June hurricanes are rarer still, though, not unheard of.  Every few years a tropical storm develops early in the season and on occasion they intensify into a hurricane.  Hurricane Agnes was an infamous, though minimal, hurricane when it made landfall in June 1972. 

 

However, the majority of the damage from Agnes came from the flooding its remnants caused in the Mid-Atlantic and Northeastern United States.  Allison was a minimal, Category 1 hurricane that also developed in June and impacted the U.S. Gulf Coast in 1995.  But the strongest, most destructive tropical system to make landfall in the United States during the month of June came in 1957. 

Hurricane Audrey intensified into a Category 4 hurricane with maximum sustained winds of 145 mph when it made landfall along the Texas/Louisiana border.  Weather satellites were still a few years away so the storm and its intensity came as a major surprise among residents along the U.S. Gulf Coast.  It caused unspeakable devastation in its path virtually unheard of during the month June with an estimated $1.1 billion in damage (adjusted for inflation to 2008 figures) and claimed 416 lives.

Audrey was also the deadliest hurricane to make landfall in the United States until Katrina in 2005.  Audrey would hold the record for strongest storm to form before August until Hurricanes Dennis and Emily grew even stronger in July 2005.  Nevertheless, Audrey remains the strongest June hurricane on record.

Extreme June Heat

The shore is a good place to beat the heat.

Continuing the trend of the largely hot and dry 1993 summer across the Mid-Atlantic, June 1994 featured some exceptionally hot weather in the Nation’s Capital.  In fact, there were four record highs in a six day stretch from June 14 through June 19. The hottest day during this stretch was 20 years ago today when National Airport reached 101 degrees.  June 15, 1994, was the first June day of triple digit heat in the Nation’s Capital since 1988.  It was also the hottest day overall since it was 101 on July 23, 1991.  June 1994 featured a sweltering total of 17 days with high temperatures of at least 90 degrees – including 14 consecutive days from June 13 - 26 (1994).

What helped make June 1994 such a hot month in the Nation’s Capital was a particularly strong Bermuda High.  The Bermuda High is a sprawling, semi-permanent area of high pressure situated just off the East Coast of the United States. It’s centered near Bermuda where it gets its nickname from. In the northern Hemisphere, air circulates clockwise around an area of high pressure and that means the Mid-Atlantic Region – on the west side of the Bermuda high – would get southerly to southwesterly flow around it. That pumps large amounts of heat and humidity northward from the Deep South. 

That’s what residents of the Mid-Atlantic Region felt in earnest during the June 1994 heat wave.  Incidently, the 101 degree reading on June 15 was the hottest temperature of the entire 1994 summer in the Nation’s Capital. It wouldn’t be this hot in the Nation’s Capital again for more than three years until August 16, 1997 when it was 102 degrees – also a record high.

The hottest weather of the year is on tap this week.  However, temperatures aren't expected to read the triple digit mark.  We'll see if any triple digit heat is on tap in 2014 as we head deeper into the summer season.

What Lies Ahead for the 2014 Hurricane Season?

The 2014 season is poised to pick up where 2013 left off as being a quieter than average Atlantic Basin hurricane season.  The Atlantic Basin hurricane season averages 12 named tropical storms, 6 hurricanes and 3 major hurricanes.

A system is named a tropical storm when sustained winds around the storm center reach 39 mph and the tropical storm becomes a hurricane when sustained winds increase to 74 mph.  A hurricane becomes “major” when sustained winds around the center of the storm reach at least 111 mph, making it a Category 3 on the Saffir-Simpson Hurricane Intensity Scale (rankings go from 1 to 5).  

The 2013 hurricane season featured 13 tropical storms and 2 hurricanes.  For the first time since 1994, there were no major hurricanes in the Atlantic Ocean.  Not only were there fewer hurricanes than normal, the hurricanes that developed (i.e., Humberto and Ingrid) did not intensify significantly.  Scientists attribute the quiet hurricane season last year to a few factors.  There was significant wind shear – differing wind speeds and direction with altitude – in the Gulf of Mexico and northwestern Caribbean Sea.  For most of the 2013 season, there was also a plume of dry, dusty air that spilled off the west coast of Africa into the tropical Atlantic.  Tropical storms and hurricanes need calm winds and a moist atmosphere to develop and intensity, so the wind shear and dry air created a largely hostile environment in 2013. 

The Atlantic Basin hurricane season starts June 1 and runs through November 30, with the most active part of the season being from mid-August to mid-October when ocean temperatures are their warmest.  Led by scientists at the National Oceanic and Atmospheric Association (NOAA), the National Hurricane Center recently updated their forecast for the hurricane season.  They expect a near or slightly below average season with between 8 and 13 tropical storms, of which 3 and 6 will grow into hurricanes of which 1 to 2 will become major.  Meanwhile, a distinguished group of atmospheric scientists at Colorado State University, released their forecast for the 2014 hurricane season last month.  They expect 9 tropical storms to be named of which 3 will develop into hurricanes.

Such similar forecasts for the upcoming Atlantic hurricane season can be partially attributed to the expected return of El Nino during the summer and early fall.  “El Nino” refers to the periodic warming of the tropical eastern Pacific Ocean.  This warming creates changes in weather around the world, including the tropical Atlantic.  The presence of El Nino commonly leads to increased levels of wind shear along with cooler water temperatures in the tropical Atlantic.  Both of these factors inhibit tropical storm formation.  

Ironically, it does not matter how many tropical storms form, it’s where they develop and track that’s truly important.  For example, the 1992 hurricane season was a below average season in the Atlantic Ocean.  It began slowly with the first tropical storm not developing until mid-August.  However, that storm was the infamous Hurricane Andrew – only the third Category 5 hurricane on record to make landfall in the United States.  Hurricane Andrew was also the costliest natural disaster in U.S. history until Hurricane Katrina in 2005. 

This blog post was adapted from a story I wrote for wusa9.com.  So far the tropics look quiet – as they typically do in early June.