WINTER LEAVES TATTERED BLANKET OF SNOW
Jan. 12, 2007 — Skiers, sledders and snowmobilers in the central U.S. and East have been left itching for snow this season as El Niño influences the nation's typical winter weather pattern. In Thursday’s daily snow analysis issued by NOAA, only 26 percent of the contiguous U.S. is currently covered by snow—with the greatest aerial coverage and depths across the higher elevations of the West and with relatively paltry amounts in the upper Midwest and Northeast. (Click NOAA snow depth image for larger view showing national conditions across the USA on Jan. 11, 2007. Please credit “NOAA.”)
"The distribution of snow across the country so far this season has been uneven, to say the least. While some areas have been inundated with snowfall, others are lacking," said Don Cline, PhD., acting director of the NOAA National Operational Hydrologic Remote Sensing Center in Chanhassen, Minn. Even NOAA's snow scientists in Chanhassen are currently contending with bare ground and a seasonal snowfall currently 20 inches below average.
So far this season, the jet stream—the river of fast-moving air in the upper levels of the atmosphere—has largely flowed in a west to east "zonal" direction near the northern tier of the country. This has escorted milder Pacific air across the country while locking arctic air in Canada. (Click NOAA snow depth image for larger view showing national conditions across the USA on Jan. 12, 2005. Please credit “NOAA.”)
At times, the jet stream has dipped south, especially over the western U.S., allowing colder air to invade. When this cold air combines with moisture, heavy snow has been the byproduct over the Intermountain West, Colorado and High Plains. When the jet stream dips south over the West, it often shifts north of its normal position in the East, resulting in abnormally warm conditions over the eastern half of the country and supporting rain as the predominate form of precipitation.
Nationally, the current 26 percent snow coverage is on par to the coverage this day last year, but is much less than the 43 percent in 2005 and 33 percent in 2004.
Regionally, the Northeast had extensive snow cover in December and January during the past three seasons with 90 percent to 100 percent snow coverage much of the period and occasional decreases to around 50 percent. This year, snow cover has been much lower with much of December down to 10 percent to 15 percent, and topping out at less than 80 percent.
In the northern Great Lakes region, December started with close to 90 percent snow cover but then dropped down to about 30 percent by mid-December. Currently, the Upper Midwest has a little less snow cover than this time over the past three seasons.
In contrast, much of the West has been experiencing frequent snow storms resulting in extensive snow cover. Most notably, the central Rocky Mountains of Colorado and Wyoming currently have 90 percent to 100 percent snow cover, compared to 50 percent to 80 percent snow cover at this time during the past three years.
"This is still a young winter season, and it takes just a single storm to drop a fresh blanket of snow and chip away at mounting snowfall deficits," Cline added. He recalled the light amount of snow in January of last year in parts of the East, which was followed by an early February storm that dumped up to 28 inches of snow from the Carolinas to New England.
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