Hazy, Hot and Humid

Although the average high for August 18 has cooled slightly to 87 degrees at National Airport, mid-August can still be quite hot.  On this date in 1995, Washington, D.C., set a record high of 97 degrees.   Like the summers of 2010-2012 that I wrote about recently, 1995 also featured an unusually hot summer (including a stretch of 25 consecutive days without measureable precipitation).

The 97 degree record high set 19 years ago today would stand for seven years until 2002, when the high climbed to a sultry 98 degrees.   Washingtonians experienced a rather unique occurrence in 2002 when August was hotter than July.  The average monthly temperature – combining daytime highs with nighttime lows - for August 2002 was 90.4 degrees, while it was “only” 89.7 degrees for July.  Also, August 2002 featured two days with triple digit heat (the first triple digit heat in the Nation’s Capital since July 1999).

The summers of 1995, 2002 and 2010-2012 saw a strong ridge of high pressure situated off the Southeast coast of the United States.  This high pressure ridge helped limit rainfall while pumping up the heat and humidity for the Mid-Atlantic Region.  However, the summers of 2013 and 2014 have not seen the same record heat and prolonged dry weather. 

In fact, the Mid-Atlantic Region had only 10 days of 90 degrees or hotter weather since July.  By comparison, from July 1 through August 18, 2010, Washington, D.C. (as measured at National Airport) observed 30 days of 90 degree or hotter high temperatures.  That helps illustrate the extreme variability in weather patterns in the Nation’s Capital – and makes forecasting the weather here challenging and exciting.

Forests Under Threat in the West

Western forests have experienced a myriad of weather conditions that have led to a significant amount of deforestation in recent years.  There has been an ongoing drought dating back more than a decade across much of the Western United States that has coincided with an uptick in wildfires and extreme heat waves.  In addition, heavy rain events have caused flash flooding and that threatened a lot of forest land.

Dating back to the late 1990s, a significant portion of the Western United States experienced worsening drought conditions.  That includes below normal snowfall during the winter months.  Snowfall has particular importance in the Rocky Mountains since the spring and summer snowmelt replenishes reservoirs.  The U.S. Drought Monitor Index continues to show severe to extreme conditions throughout the Southwest and California.

These circumstances have compelled residents to conserve water.  The climate is such out West that wildfires are an elevated risk because of dry underbrush and gusty winds.  Wildfires often begin innocently, by carelessly tossed cigarettes, campfires not properly extinguished and dry lightning strikes.  The U.S. Forest Service and the U.S. Department of the Interior are responsible for fighting wildfires across the country.  They concluded recently that they “may need to spend $1.8 billion fighting fires this year, while the agencies have only $1.4 billion available for firefighting.” 

Mountain pine beetles have also caused a considerable amount of damage to trees as far South as New Mexico and all the way North to Montana.   The pine beetles attack trees by laying their eggs and burrowing into the bark.  Once they hatch, the larvae grow and cause even more tree damage.  Recent winters have not been as cold in the Rocky Mountains as in decades past allowing pine beetles to survive and reproduce more quickly.

Due to the increasing amount of deforestation caused by drought, wildfires and pine beetles, flash flooding is an increased risk.  Exposed hillsides are less able to absorb water in a heavy rain than wooded areas are.  Although the summer monsoon season has helped ease drought conditions in the desert Southwest, it will take a more permanent shift in the overall weather pattern to end the chronic drought.  Like the Mid-Atlantic forests I recently wrote about, the forests in the Western United States contain an enormous amount of biodiversity and provide a natural way for the air to the cleanse itself.  That is why preventing deforestation is so important.

Weather Quiz

Weather records show that Florida has seen the highest number of major hurricanes with 37 since 1851.  Which state is number 2 on the list?

A.    Texas

B.     North Carolina

C.     Louisiana

D.    Mississippi

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Answer to question from July 29^th:

True or False:

Hurricanes, typhoons and cyclones are all the same type of storm.  The only difference between them is the part of the world that they form in.

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True.  

Hurricanes, typhoons and cyclones are all the same type of storm.  They are all tropical storms that intensify over warm ocean water with sustained winds of at least 74 mph around the center of the storm.  They are called hurricanes in the Atlantic Ocean, the Central and Eastern Pacific Oceans.  West of the International Date Line, they are called typhoons.  They are called cyclones in the Indian Ocean and around Australia.  There are different lists of names, too, depending on the part of the world a tropical storm forms in.

Heat? What Heat?

Triple digit heat is a true rarity for the Mid-Atlantic Region. That’s because triple digit weather is most common in arid climates away from water. Meanwhile, summers in the Nation’s Capital are often very humid. When the air is more humid, it cannot heat up or cool down as quickly. This is why summers are so hot in the desert southwest while in the southeastern United States – where the weather is heavily influenced by the Gulf of Mexico and Atlantic Ocean – triple digit heat is rarer.

It only reaches the century mark every few summers in the Nation’s Capital. Prior to 2010, no triple digit heat had been experienced in Washington, D.C., since 2007.  This demonstrates how rare a single day with triple digit heat is for Washington, D.C.  It’s even rarer for there to be multiple days with triple digit heat in the Mid-Atlantic Region.  

But that’s exactly what made the summers of 2010 through 2012 so unusual. 2010 had four days of triple digit heat while 2011 had five and 2012 had eight. In fact, July 2012 set a new record for most 100 degree days in a month with seven.  The last summer to feature five 100 degree days in the Nation’s Capital was 1997.  As hot as those three summers were, last summer and so far this summer have combined to feature less extreme heat in the Mid-Atlantic Region.  In fact, it hasn’t been 100 degrees at National Airport (Washington, D.C.’s official weather reporting site) since July 26, 2012.

A Cleaner Future for the Chesapeake Bay?

Three of the four largest U.S. cities are on or near a prominent body of water, including New York City, Chicago and Los Angeles.  While not far from the Atlantic Ocean, our Nation’s Capital of Washington, D.C. is closer to a smaller body of water that plays a crucial role in the ecology of the Mid-Atlantic Region.  The Chesapeake Bay is heavily relied upon for both fishing and recreation.  That makes preserving the Bay a critical issue for our region.

The Chesapeake Bay is nearly 200 miles long and has 4,600 miles of shoreline.  It acts as a buffer every time a large storm comes up the East Coast by protecting the shore from coastal erosion.  Much like the Louisiana bayous, the Chesapeake Bay plays a vital role in the region’s ecology.  When major weather systems like Hurricane Isabel in 2003 and former Hurricane Sandy in 2012 came through the Mid-Atlantic Region, the Chesapeake Bay helped absorb a lot of the storm surge.

However, as the Mid-Atlantic Region and Northeast U.S. has become more developed, the Chesapeake Bay has been significantly damaged by the associated pollution.  Some of the major industrial pollutants include nitrogen, as well as fertilizer and pesticide runoff from agriculture. The largest source of nitrogen in the Bay is from agricultural runoff.  After it rains, the many tributaries that flow into the Chesapeake see an influx of nitrogen runoff that eventually makes its way into the Bay.  One of the EPA’s primary plans to reduce this pollution is to ensure that localities “…will have to install grassy ditches and restore natural streams in place of concrete channels. The idea is to slow down runoff and let it seep into dirt and roots.”  

Prolonged stretches of dry weather can be just as damaging to the Bay as heavy rain.  The Mid-Atlantic experienced three of the hottest summers on record from 2010 through 2012.  The combination of extreme heat and dry weather helped lead to “dead zones” on the Bay (or areas where no oxygen is present) to the detriment of wildlife.

The Maryland Department of Natural Resources reported in May 2014 that there were only 69 million spawning-age female blue crabs, which is below the minimum safe level of 70 million.  Scientists attribute the reduced number of spawning-age female blue crabs to the long, cold 2013-2014 winter season.  However, they also reported the good news that the overall number of the Chesapeake Bay’s signature blue crabs is at its highest level in at least six years.  

Conservation and environmental protection are critical to ensure the health of the Chesapeake Bay for future generations.  Residents of the Mid-Atlantic Region and Northeast can do their part by reducing their usage of fertilizers and pesticides by choosing greener, non-toxic products.

The Health of Our Forests Depends on the Weather

The relationship between drought and deforestation is a complicated one that impacts local ecosystems and large scale weather patterns.  For example, three of the hottest summers on record occurred in the Mid-Atlantic from 2010-2012 concurrently with a period of chronic drought.  That led to some loss of forest land in the Eastern United States.  Recent years have also seen a series of major storms, including the June 2012 Mid-Atlantic “derecho” (long lasting line of severe thunderstorms) and former Hurricane Sandy in October 2012, which contributed to loss of forest land.   

If this continues, then there may be long-term effects on weather and climate patterns.  Forests and parks are invaluable natural resources that provide a cooler oasis for city dwellers to visit.  They also perform the critical function of converting carbon dioxide to oxygen that mammals breathe.

The combination of below average rainfall and above average summer heat during the three consecutive summers through 2012 depleted some forest land across parts of the Eastern United States – including the Mid-Atlantic Region. A recent study done by NASA found that “nearly 40% of the Mid-Atlantic’s forests lost tree canopy cover, ranging from 10% to 15% between 2000 and 2010…”

Countless record highs were set during the summers of 2010 through 2012.  At National Airport, July 2012 featured 7 days of triple digit heat, breaking the previous record of 6 set in July 1930.  That was in conjunction with below average rainfall, making it especially tough on vegetation.  People living in the region will remember those summers as being particularly hot and dry.

Although the summers of 2013 and 2014 have featured less extreme heat, there have been several instances where rounds of severe weather have knocked down significant numbers of trees.  The good news is that a lot of the older trees had already been knocked down or cut down so there have been fewer widespread power outages than in recent years.  However, losing a significant portion of forest has key environmental effects including a decrease in biodiversity and the ability of the environment to cleanse and cool itself.