Tropical Storms in December?

Tropical Storm Zeta (12-30-05)   Source: NASA

The tropical season typically ends quietly on November 30.  The final storm to form during the 2014 hurricane season was Tropical Storm Hanna on October 22.  While this was a relatively quiet season, 2005 was anything but for the Atlantic Ocean Basin.

More named tropical systems formed in 2005 than any other season (June 1 to November 30) on record. A total of 28 tropical storms formed, of which 15 became hurricanes with sustained winds of at least 74 mph. Of those 15 hurricanes, 7 became major hurricanes defined as being Category 3 (out of 5) or greater on the Saffir-Simpson hurricane intensity scale with sustained winds of at least 111 mph.

Moreover, 2005 produced a record four Category 5 hurricanes as well.  That included the strongest hurricane ever recorded in the Atlantic Ocean – Hurricane Wilma.  The most infamous storm of the 2005 season was Hurricane Katrina, which surpassed Hurricane Andrew as the costliest natural disaster in U.S. history.  According to the National Hurricane Center, Katrina caused an estimated $108 billion in damage.

So many storms formed in 2005 that all the designated names on the normal list of names were used up, and scientists had to start using names based on the Greek Alphabet.  Overlooked among these records and destructive storms was the final named system of the 2005 season that formed nine years ago today. Tropical Storm Zeta formed on December 30, 2005.  Its highest sustained winds climbed to 65 mph before it dissipated on January 6, 2006, thus bringing an end to the historic 2005 hurricane season.

Snow, Sleet and Freezing Rain !

February 2007 Ice Storm (Freezing Rain, Sleet accumulations) - Source: NWS

Last winter the Mid-Atlantic Region had one of its coldest and snowiest winters on record.  That was true despite the fact that last December was over 2.5 degrees warmer than average in the Nation’s Capital.  Washingtonians are on the borderline between snow, sleet, freezing rain and rain when winter storms take shape. 

Depending on the storm track, we could see all snow, all rain or a wintry mix. This is because of the unique geography that exists in the Mid-Atlantic Region.  Being a relatively short distance from two bodies of water, the Atlantic Ocean and Chesapeake Bay, temperatures are often slightly warmer than they would be away from a large body of water.  A difference of a few degrees can make a huge difference when forecasting winter precipitation.  Areas south and east of the Nation’s Capital tend to see much less snowfall than their neighbors to the north and west of town because of this. 

All precipitation falls from the clouds as ice crystals since the temperatures at that altitude are cold enough to support ice. If the column of air that extends from the cloud to the ground remains below freezing the entire distance, then the ice crystals will fall as snow.  Snow is the easiest type of winter precipitation to deal with since it can be plowed and shoveled.

But, if a portion of the column of air between the cloud and the ground is above freezing, then that presents a new host of problems. For example, if there is a column of above freezing air just above the ground then the ice crystals – or snowflakes – melt into raindrops.  If the surface temperature is below freezing, then these raindrops will refreeze upon reaching the ground creating “freezing rain.”

On the other hand, if the column of air with above freezing temperatures is higher in the sky with a greater amount of below freezing air above the ground, then the water droplets have a chance to refreeze into “sleet” pellets before hitting the ground. Sleet can accumulate like snow, but tends to be heavier than snow because the water content is higher which suppresses accumulations.  That’s because sleet compacts more than snow does keeping accumulations lower than if it were pure snow.

Weather Quiz

Tornado observed in Oklahoma   Source: NOAA

Although rare, December tornadoes do occur on occasion as we’ve seen this week along the U.S. Gulf Coast.  Which month averages the fewest tornadoes in the United States?

A.  November

B.  January

C.  December

D.  February

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Answer to question from December 15

B.  Washington, D.C. averages a White Christmas roughly once every five years.  See my December 21 post for more details.

Longing for a White Christmas?

December 2009 MD Snow

A lot of people wonder in the days before Christmas whether or not a “White Christmas” is in the cards for where they live.  It’s more likely in some parts of the country than others – like in the Upper Midwest or the Great Lakes Region where lake effect snow is common.  In the Mid-Atlantic Region, snow on Christmas is relatively uncommon.  To read in more detail about the last time there was a “White Christmas” in the Nation’s Capital check out this story I wrote for the WUSA9 website.

Record December Snowfall gave Washington, D.C. a White Christmas

Snowfall Accumulations December 2009 (Source: NOAA)

Many will remember the major winter storm that began on this date five years ago. Spanning several days, this storm brought the Mid-Atlantic Region (including Washington, D.C., Baltimore, MD, and Philadelphia, PA) its largest December snowfall on record. It was a classic “Nor’Easter” that developed and tracked in the perfect location to bring prodigious snowfall to much of the I-95 corridor.

Meteorologists first identified the developing storm on December 16, 2009, along the U.S. Gulf Coast.  Snow began falling in the Nation’s Capital during the evening of December 18.  However, the bulk of the snow fell on December 19 with a daily record of 15.0” observed at National Airport.  That was not only the largest daily snowfall total for December 19, but the largest snowfall ever observed in the Nation’s Capital during the month of December. 

Total snowfall accumulations from the record December storm ranged from 15” to 25” across the D.C. Metropolitan area.  A storm total of 16.4” occurred at National Airport, making it the 7^th largest snowstorm on record in the Nation’s Capital.  The storm brought 18.0” to Dulles Airport making it their 5^th largest snowstorm on record; and the 18.0” in Baltimore were good enough to place 10^th on their list of largest snowstorms.  Roads were impassable which forced many schools and businesses to close for several days.  This was especially troublesome for business and holiday shoppers alike amid the holiday season. 

Snow lovers rejoiced, though, as enough snow fell the week before Christmas to ensure that some would remain on the ground for the holiday.  Officially, there was 7” of snow on the ground downtown on Christmas 2009.  The largest December snowstorm on record in the Nation’s Capital left an indelible mark on Washingtonians and millions of people across the Eastern United States.

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.