Weather Quiz

Exploring a fresh snow, December 2009

How often does Washington, D.C. see snow on Christmas?

A.     Every Two Years

B.      Every Five Years

C.      Every Ten Years

D.     Every Twenty Years

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Answer to question from December 7:

B.  Flooding. 

According to the University Corporation for Atmospheric Research and Centers for Disease Control, flooding causes more fatalities in a given year in the United States than any other natural disaster.

Why Care about the “Wind Chill?”

Scale of approximate "wind chill" given certain conditions

Now that we’re into December, this is a good time to review what “wind chill” is.  During the winter, air temperature isn’t always an accurate measure of how cold you feel outside.  The strength of the wind often acerbates the intensity of the winter cold.

“Wind chill” is the temperature it will actually feel like as the wind blows the heat away from exposed skin.  Consequently, only living things such as people and pets will feel the effects of wind chill.  However, when wintery precipitation is in the forecast, the air temperature is all that matters.  That’s because even if the wind chill is below freezing, water will not freeze if the air temperature is above freezing.

The summer equivalent of “wind chill” is the “heat index.”  The “heat index” is the temperature it actually feels like out when you combine the air temperature with the relative humidity.  As Washingtonians commonly experience during the summer months, the higher the relative humidity is, than the higher the “heat index” will be.  As in the case of “wind chill,” inanimate objects do not feel the “heat index.”

Measuring Snowfalls like the Pros Do

Measuring Record Snow in February 2010

With a major winter storm bringing significant snowfall today in the Northeastern United States, this is a good time to review some simple ways to measure snow accurately.  You should use a flat piece of wood or other light material – preferably white – and place it on a solid, lightly colored surface.  This is called your “snow board.”  White is a highly reflective color that doesn’t become artificially warm by absorbing solar heat. 

 

There are a few simple things you can do before the flakes start falling.  Walk around your yard and identify several spots that are good for taking measurements.  A flat, lightly colored surface away from any structures and free of any overhanging items like branches, signs or awnings is best.  Being away from buildings eliminates any temperature or wind influence from the structure which could affect snowfall accumulations.  Also, since darker colors absorb more heat from the sun and other light sources, it’s ideal to find a lightly colored and flat, but firm space – such as a sidewalk – to place your “snow board.”

During a winter storm take a yard stick or ruler and measure the accumulation by pressing until it hits the “snow board.”  After taking the measurement to the nearest tenth of an inch, promptly clear off the snow and place your board back on its spot. 

You can measure the snow as often as you like, but try to keep a regular schedule such as measuring and clearing your “snow board” four times per day or every six hours during the snowfall.  For those not using a “snow board,” take five to seven measurements and then eliminate your highest and lowest values.  Of the remaining values, average them together and then you’ll have an accurate storm total.  Taking multiple measurements reduces the amount of uncertainty in your data.

Weather Quiz

What is the deadliest type of weather in an average year in the United States?

A.  Hurricanes

B.  Flooding

C.  Lightning

D.  Heat Waves

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Answer to Weather Quiz question from November 27

C.  Odile was the strongest – and most destructive – hurricane to hit the southern peninsula of Baja California since Olivia in 1967.  Fortunately, the recovery efforts across Cabo San Lucas and much of the other affected areas are well underway.  However, it will take some time to get everything repaired and operational to pre-storm levels.

Although fringe effects (such as choppy surf, gusty winds and light rain) of weakening tropical storms are fairly common, direct hits from major hurricanes are not common in Baja California. This can be attributed to the predominant local wind patterns.  

The prevailing wind patterns in the tropical Eastern Pacific – west of Mexico – blow from east to west (the same as the winds blow off the west coast of Africa in the Atlantic Ocean).  Only rarely are conditions such that a hurricane is able to deviate from these predominant wind patterns.  

Odile was one of those rare hurricanes.

Snow in Early December - What Does it Portend?

DC Area Snow Totals (12-5-2005)   Courtesy: NWS-LWX

The month of December averages a modest 2.3” of snow at National Airport and 3.5” at Dulles Airport. However, today’s date has featured widely varying amounts of snow over the last two decades.  Dating back to 1996, Washingtonians have experienced snow an astounding seven times on December 5.

The winter of 1996-1997 was relatively mild, but on this date in 1996, 1.1” of snow was observed at Dulles Airport. That was a relatively minor occurrence, unlike what happened on this date in 2002. That’s when a record 6.1” of snow fell at National Airport and a record 6.2” fell at Dulles Airport.

On this date in 2003, snow totals in the suburbs north and west of Washington, D.C. varied from 1” to 8”. In three consecutive years starting in 2005, December 5 saw snowfall across the Nation’s Capital. Only flurries were observed in 2006, but 2.6” fell in 2007. As recently as 2009, 0.1” of snow fell at National Airport.

As we saw, the snowfall five years ago today in 2009, was merely a harbinger of what would become not only the snowiest December on record with 16.6” at National Airport, but the snowiest winter season on record for the Nation’s Capital. By comparison, on December 5, 2013 the high temperature in the Nation’s Capital climbed to 69 degrees.  Ironically, last winter ended up being both colder and snowier than average. That fact illustrates that early season snow does not directly correlate to a cold and snowy winter.