Weather Quiz

Happy Halloween !

True or False.

Dating back to 1993, only two Halloweens have featured measureable rainfall in the Nation’s Capital.

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Answer to Weather Quiz question from October 19.

C.  Hurricane Wilma was not only the strongest hurricane on record in the Atlantic Ocean, but was the record fourth Category 5 hurricane to form during the 2005 season.

Will Halloween Bring Tricks or Treats?

October sunset in Poolesville, MD  (Courtesy: Ashley Adams)

Late October typically brings the Nation’s Capital a high degree of variability in the weather from one year to the next.  That contributes to making it especially challenging to accurately forecast the weather on Halloween more than a few days in advance.  A good example of this changeable weather occurred on this date in 1996 when a record high temperature of 82 degrees was set at National Airport.

By contrast, Washingtonians saw a truly rare event on October 29, 2011 when the first snow of the season fell.  Temperatures also remained more than 20 degrees below average as the daily high temperatures at both National and Dulles Airports hovered close to 40 degrees.  That left many longing for the record warmth experienced in 1996.

Such radically different weather conditions can be largely attributed to the position of the jet stream.  In 1996, the jet stream was well to our north, which allowed an area of high pressure (situated off the east coast of the United States) to usher in the record warmth.  However, there was a significant dip in the jet stream 15 years later that facilitated the significantly colder than average weather in 2011.  According to the National Weather Service, today’s average high is 64 degrees at both National and Dulles Airports.

Temperatures have been cooler than average with highs remaining in the 50s on three of the last four Halloweens.  High temperatures are poised to be around 60 degrees tomorrow in Washington, D.C.  The coldest Halloween during the last 20 years in the Nation's Capital came in 2002, when it was only 47 degrees; while the warmest Halloween to occur in recent memory was in 2004 when it was 79 degrees.  Many trick-or-treaters may also remember that measurable rain hasn’t occurred in the DC Metro Region on Halloween since 2009.  Looking ahead to the first week of November next week, temperatures will feel more like September, as it will soar well into the 70s across the Mid-Atlantic Region. 

Tomorrow night is also when Daylight Saving Time ends, so we need to set our clocks back one hour.  The good news about changing the clocks back is that it will make this weekend 49 hours long.  In the interest of safety, it’s a good idea to also change the batteries in our smoke and carbon monoxide detectors this weekend.

October’s Surprising Weather

Roosevelt Island is Beautiful in the Fall

Washington, D.C.’s warmest October temperature on record was 96 degrees (on October 5, 1941).  However, this fall it hasn’t been 90 degrees since September 9 when it was 94.   In fact, the warmest temperature this month in the Nation’s Capital was 79 degrees on October 9.  The coolest temperature so far this month occurred on October 19 when the low fell to 37 degrees.  However, temperatures fell to the upper 20s the very same morning.

The warmest October on record in the Nation’s Capital was in 2007 when the average monthly temperature (combining daily highs and lows) was 67.1 degrees, compared to a monthly average of 59.5 degrees.  The coolest October on record in the Nation’s Capital came in 1876 when the average temperature was 50.7 degrees.  Modern weather observations in Washington, D.C. have been made at National Airport since it opened in 1941.

Meteorological fall runs from September 1 through November 30.  Meteorologists break up the seasons into equal three-month periods for the ease of averaging climate data.  This fall got off to a torrid start in the Nation’s Capital, with seven of the first ten days of September seeing high temperatures in the 90s.  Although September was nearly four degrees warmer than average in Washington, D.C., the pendulum has swung the other way in October.  So far this month, there have been five days with highs in the 50s in the Nation’s Capital, which is more characteristic of the second half of November.  Through October 26, this month has been a full degree cooler than average in Washington, D.C.

Last week, Hurricane Patricia became the strongest hurricane on record in the Western Hemisphere.  That’s typical of an El Nino year when conditions are favorable for more frequent and more intense hurricanes in the Eastern Pacific Ocean.  The remnants of Hurricane Patricia will enhance the rainfall across the Mid-Atlantic Region tonight and tomorrow.  However, no high winds or flooding rains are expected.

The Mid-Atlantic Region has felt the impacts of former tropical storms and hurricanes in October several times.  In October 1995, the remnants of Hurricane Opal brought appreciable rainfall and a few tornadoes to the Maryland suburbs of Washington, D.C.  Just three years ago, the Mid-Atlantic Region felt the frightening impact of Sandy.  At one point, Sandy was a major Category 3 hurricane while over the open ocean, but weakened before coming ashore.  The DC Metro Region saw record rainfall from Sandy as 3.85” of rain fell on October 29, 2012.  Fortunately, rainfall totals like that aren’t expected from the remnants of Patricia.

Putting Patricia into Perspective

Category 5 Hurricane Patricia (Source: UW-Madison)

Hurricane Patricia has set a new all-time record for strongest hurricane in the Western Hemisphere.  Patricia rapidly intensified from a tropical storm to a Category 5 hurricane in only 24 hours.  In just one day, its sustained winds increased by 110 mph, which is among the fastest rates of hurricane intensification anywhere in the world. 

On Friday, October 23, a hurricane reconnaissance flight measured Patricia’s sustained winds at 200 mph with a minimum air pressure of 880 millibars (Patricia’s lowest air pressure was ultimately 872 millibars).  Air pressure is generally considered a more accurate measure of the intensity of a hurricane.  The lower the air pressure, the stronger the storm is.  Standard sea level air pressure is approximately 1013 millibars.  According to the National Hurricane Center, Hurricane Linda in 1997 was the previous strongest hurricane in the Eastern Pacific Ocean.  Also a Category 5 hurricane, Linda's highest sustained winds were 185 mph with a minimum air pressure of 902 millibars.  The strongest hurricane on record in the Atlantic Ocean was Hurricane Wilma in 2005, with maximum sustained winds of 185 mph and a minimum air pressure of 882 millibars.

While Hurricane Patricia became the strongest hurricane on record in the Western Hemisphere, it ranks as the second strongest hurricane to form worldwide.  Only Typhoon Tip was stronger in 1979.  According to the Japanese Meteorological Agency, Tip remains the world’s strongest hurricane on record with a minimum air pressure of 870 millibars (its highest sustained winds were 190 mph).  Hurricanes are known as typhoon west of the International Date Line in the north Pacific Ocean.

In addition to having had the lowest air pressure of any hurricane in the Western Hemisphere, Patricia also had the highest sustained winds at 215 mph.  The previous record-holder in the Western Hemisphere was 1980’s Hurricane Allen, which was another Category 5 storm that had peak sustained winds of 190 mph.  To help put Patricia’s maximum sustained winds of 215 mph into perspective: that’s equivalent to an EF-5 tornado on the Enhanced Fujita Scale - as strong as tornadoes get.

Hurricane Patricia came ashore last night on the West coast of Mexico as a Category 5 storm – capable of catastrophic damage.  The last Category 5 hurricane to make landfall in North America was Dean in 2007 (on the east coast of Mexico).  The remnants of Patricia are expected to bring rain to Texas which is bad since Texas is already experiencing dangerous flooding.