National Oceanic and Atmospheric Administration

National Climatic Data Center, 14 February 2001

• Climate of 2001: January
• Detailed Climate Perspectives . . .
  • Global Analysis
    
  • Global Regional
    
  • U.S. National
    
  • U.S. Regional
    
  • U.S. Drought
    
  • Extreme Events
• 2001 Monthly Reports

Contents of This Report:

• North American 500 mb Maps
• January National Temperature
• January National Precipitation

The North American 500 mb Maps for January

The upper-air pattern during January reflected positive height anomalies over central Canada and the north central United States which were associated with above normal surface temperatures. A series of upper-level troughs moved across the southern U.S. bringing below normal temperatures. Additional information on hydrometeorological analysis and forecasting can be found at the Hydrometeorological Prediction Center's Web Page. The principles behind the 500 mb flow are briefly explained here.

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National Temperature - January

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The graph to the left shows January 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. January 2001 ranked near the middle of the historical distribution. The preliminary nationally averaged temperature for January 2001 was 31.7° F (-0.2° C) , 0.9° F (0.5° C) above the long-term mean. The actual January temperature values from 1895 through 2001 are available. About three percent of the country averaged much warmer than normal and less than one percent much colder than normal.

The map to the right, based on approximately 250 airport stations, shows departures from the 1961-1990 normal temperatures for January 2001. In general, the southeast portion of the country was cooler than normal while the north central areas were above normal. Most of the Alaska and Hawaii reporting stations were warmer than normal. The day-to-day temperature variability was generally below normal across most of the country.

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The standardized temperature anomalies for January 2001 were above normal in the north central states and below normal in the southeastern U.S. The month averaged near normal across most of the rest of the country. The map animation provided shows the geographical pattern of temperature anomalies for the last 12 months compared to a base period of 1931-1990.

National Precipitation - January

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Based upon preliminary precipitation data, January 2001 ranked as the 14th driest such month since records began in 1895. This contrasts sharply with the unusually wet conditions that dominated January during most of the 1990's.

The preliminary national standardized precipitation index ranked January 2001 as the 34th driest January, tying with 1940. About four percent of the country was much wetter than normal and about ten percent was much drier than normal.

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The map to the right, based on approximately 250 airport stations, shows January 2001 total precipitation as a percent of the 1961-1990 station normals. Above normal precipitation generally occurred over the central and southern Plains and parts of the Southwest. Below normal precipitation occurred over much of the rest of the country including the Hawaiian stations. The precipitation pattern over Alaska was generally dry in the interior and wet along the north and south coasts.

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Snow cover duration for January 2001, as observed by satellite, exceeded the 1992-2001 average over much of the nation in a broad path from New England to the southern Plains and southwest and into the western mountains. Although snow cover extent in the western U.S. (as shown in the extent and duration map to the left) was greater than the 1992-2000 average, snow depth as indicated by mountain snowpack was well below the 1961-1990 average in many western river basins. An animated map of daily snow cover occurrence shows the daily progression of snow for January.

Huron, SD recorded 28.7 inches (72.9 cm) of snow this month, which breaks the previous January record of 27.7 inches (70.4 cm) set in 1977. In contrast, only 3.4 inches (8.6 cm) of snow fell at Detroit, MI during January 2001, which compares to a 1961-1990 normal of 10.0 inches (25.4 cm). The daily snow depth from stations across the country for the last week of January can be seen by clicking here.

Syracuse International Airport, NY, set a seasonal snowfall record of 103.2 inches (262.1 cm) on January 5th. Amarillo, TX had 10.0 inches (25.4 cm) of snow on the ground as of January 1st which tied the maximum snow depth of 10 inches reported during January 1987.

Data collected by NOAA's TIROS-N polar-orbiting satellites and adjusted for time-dependent biases by NASA and the Global Hydrology and Climate Center at the University of Alabama in Huntsville indicate that temperatures in the lower half of the atmosphere (lowest 8 km) were the third coldest since 1979 over the U.S. for January 2001. This is the second consecutive month temperatures were much below the mean. The average lower tropospheric temperature over the continental U.S. was 0.75° F (0.4° C) below the 1979-1998 mean.

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Current data are based on preliminary reports from River Forecast Center stations and First and Second Order airport stations obtained from the National Weather Service (NWS) Climate Prediction Center and real time Global Telecommunications System (GTS) monthly CLIMAT summaries. THE CURRENT DATA SHOULD BE USED WITH CAUTION. These preliminary data are useful for estimating how current anomalies compare to the historical record, however the actual values and rankings for the current year may change as the final data arrive at NCDC and are processed.

The following NCDC datasets are used for the historical U.S. data: the climate division drought database (TD-9640), and the hurricane datasets (TD-9636 and TD-9697). It should be noted that the climate division drought database consists of monthly data for 344 climate divisions in the contiguous United States. These divisional values are calculated from the 6000+ station Cooperative Observer network.

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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