National Climatic Data Center, 15 January 2002

National Highlights:

• 12th warmest December
• Near normal to above normal temperatures in every contiguous state
• December precipitation near normal
• East Coast states dry

Contents of this Section:

• Significant Weather Events
• National Temperatures
• Temperature Departures
• National Precipitation
• Precipitation Anomalies
• National Snow Cover

Significant Weather Events

National Temperatures

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The graph to the left shows monthly mean temperature averaged across the contiguous United States based on long-term data from the U.S. Historical Climatology Network (USHCN). The 2001 value is estimated from preliminary Climate Division data using the first difference approach. December 2001 ranked as the 12th warmest December in the 1895 to present record. The preliminary nationally averaged temperature was 36.6� F (2.6� C) which was 3.2� F (1.8� C) above the long-term mean. The December temperature values from 1895 through 2001 are available.

It is interesting to note that December temperatures in only one of the last nine years were below normal. The Mean 500mb Height and Anomalies chart shows an area of positive anomalies over the East Coast states which was associated with above normal temperatures. A more detailed analysis including how statewide and regionwide temperatures compare to other years is available.

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Temperature Departures

The map to the right, based on approximately 250 airport stations, shows departures from the 1961-1990 normal temperatures for December 2001. Portions of the southwestern quarter of the country had negative temperature anomalies while most of the rest of the contiguous states experienced positive temperature anomalies. The largest positive anomalies of 9� F (5� C) were over the Midwest and Northeast. Alaska was generally much cooler than average while Puerto Rico and Hawaii were warmer than average.

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The unusually warm departures of monthly mean temperature were associated with above normal persistence of daily temperatures. This is reflected in below normal day-to-day temperature variability across the upper Midwest and the Northeast, as seen both in the map to the left and in an animated map of daily temperature anomalies.

National Precipitation

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The graph to the left is a time series depicting precipitation averaged across the nation. Based upon preliminary precipitation data, December 2001 was near average, ranking in the middle of the historical distribution. While nationally averaged precipitation was near the long term mean, there was considerable regional variability. South Dakota and Nebraska were notably dry receiving much below normal precipitation for the month.

On the 13th, a strong storm system moved in to California causing high winds, heavy rains and snowfall. Winds at South Lake Tahoe, CA gusted to 54 mph (38 m/sec) and lower elevation stations received up to 2.5 inches (63.5 mm) of rain while high mountain stations were blanketed with up to two feet (61 cm) of new snow. On the 15th and 16th, fierce storms spawned at least one tornado and gave north Texas as much as 10 inches (254 mm) of rain. Flooding and hazardous weather were blamed for several deaths in Texas and Arkansas. On the 20th, a rare tornado with hail and heavy rain affected the Los Angeles, CA area, downing trees and power lines.

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Precipitation Anomalies

The map to the right, based on approximately 250 airport stations, shows December 2001 total precipitation as a percent of the 1961-1990 station normals. Above normal precipitation generally occurred from central California northward to Washington, from east Texas northward along the Mississippi River Valley, east of Lakes Erie and Ontario, in southern Florida and in Puerto Rico. The rest of the country was mostly dry including Alaska and Hawaii.

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National Snow Cover

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The map to the left shows national snow cover as of the 31st. By far the biggest snow story of the month was in Buffalo and other areas east of Lakes Ontario and Erie where an extended period of lake effect snows left up to 130 inches (330.2 cm) of snow on the ground in Montague, NY. Some of these areas have received almost their entire normal winter snowfall from this one event. Table 1 shows snowfall data for Buffalo, NY and Map 1 depicts snowfall totals from the 24th-31st event.

Questions?

For all climate questions other than questions concerning this report, please contact the National Climatic Data Center's Climate Services Division:

For further information on the historical climate perspective presented in this report, contact:

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