Climate: U.S. temps cooler than average in 2013

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Cooler than average temperatures were widespread across the U.S. in December 2013.

California drought intensifies

By Summit Voice

FRISCO — December 2013 won’t go down in the record books for cold temperatures even though cooler-than-average readings prevailed across much of the country.

The average temperature across the lower 48 states was 2 degrees Fahrenheit below the 20th century average, making it the coldest December since 2009, according to the monthly summary released this week by NOAA’s National Climatic Data Center.

Cool readings were widespread across the West, the Plains States, and the Upper Midwest, with Minnesota and North Dakota reporting temps that ranked among the 10 coolest years on record.

The only parts of the county that were warmer than average were the Southeast and parts of the Mid-Atlantic, with Florida reporting its sixth-warmest December, as temperatures ran about 5 degrees Fahrenheit above average.

Several major snow storms that hit the Intermountain West, Northern Plains, Midwest and Northeast during December. As a result, snow cover extent was 317,000 square miles above the 1981-2010 average, and the eighth-largest December snow cover on record, according to the Rutgers Global Snow Lab.

The West

Other than California, New Mexico and Arizona, the West was cooler than average in December, with a persistent ridge of high pressure over the West Coast steering cold snowstorms toward the Great Basin and the Rocky Mountains.

Drought conditions persisted across the far West from Los Angeles northward to Oregon and into parts of Idaho. Parts of the California coast were record-dry, including San Francisco, which only tallied 5.59 inches of rain for the year — making it the driest year on record, dating back 164 years.

Farther north, Shasta Dam received no December precipitation for only the second time in a 71-year record. Precipitation in this key watershed totaled 16.39 inches  for 2013, far below the previous record low of 27.99 set in 1976.

For December, downtown L.A. reported only 0.24 inches if rain, just 9 percent of normal. For the year, rainfall totaled just 3.6 inches, nearly half an inch less than the previous driest year on record.

Snowpack conditions were dismal in the Sierra Nevada and Cascades at month’s end, with snow water equivalent values at less than 50 percent of median. Snow water equivalent values in the Intermountain West were at about 50-75 percent of median. The lack of snow impacted ski resorts over the holiday season, many operating only a fraction of their terrain or still closed.

Farther inland, it was a different story, with wet conditions across central Nevada, the northern Rockies and eastern Montana, including Billings, which reported its wettest December on record, while Casper reported its third-wettest December.

Parts of the Great Basin saw near-record cold temperatures in December. In Winnemucca, Nevada, temperatures averaged 18.1 degrees Fahrenheit for the month, the second coldest December in a 137-year record. The December average temperature in Boise, Idaho was 23.9 degrees Fahrenheit, making it the sixth-coldest on record, while Salt Lake City tallied its eighth-coldest December.

 

Cold temperatures in the Intermountain West also led to air quality problems in places like Salt Lake City, Boise and Reno, where strong inversions trapped cold air and pollutants near the ground.

In Salt Lake City, there were 10 days in December when the air quality was deemed “unsafe for sensitive groups.” The 5-year average for Salt Lake City in December is 4 days “unsafe for sensitive groups” and zero days “unhealthy.”

Information compiled from the NOAA National Climatic Data Center, State of the Climate: National Overview for December 2013, published online January 2014, retrieved on January 15, 2014 from http://www.ncdc.noaa.gov/sotc/national/2013/12.

 

 

 

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