Reconstructed North American Snow Extent, 1900-1993


This data set contains reconstructed monthly North American snow extent values for November through March, 1900-1993. Station-based snow observations are available for dates since the early twentieth century but lack comprehensive spatial coverage. A remotely sensed product based on visible-band imagery provides more complete spatial coverage but has been available only since the early 1970s. Investigators used a combination of satellite and station observations and based the reconstruction on linear regressions between the two types of observations. Additionally, the data set includes standard errors of estimates and the observed values upon which the regressions were based.

The figure above shows the reconstructed time series for North American snow extent, February, 1900-1993. Red dots are observed values and blue bold lines are reconstructed values. The figure also shows reconstructed values ± 1 standard error (blue solid lines). Note that reconstructed values can underestimate the magnitude, but not the sign, of the variations.

Since the reconstructed values of snow extent are based on regression, variability in extent is underestimated, and therefore the magnitude of some extreme extent values is underestimated. However, in no case during the satellite era, when both data sets were available, was the sign of the reconstructed deviation from the mean extent different than observed.

Data are available as ASCII text files via FTP.

Citing These Data:

Citations for use of this data should read:

Frei, A., and D. Robinson. 2002. Reconstructed North American snow extent, 1900-1993. Boulder, CO: National Snow and Ice Data Center.

Table of Contents

1. Contacts
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information


Investigator(s) Name and Title:

Dr. Allan Frei
Department of Geography, Hunter College
City University of New York
Rm 1006, North Building
695 Park Avenue
New York, NY 10021
Telephone: 212-772-5322
Fax: 212-772-5268

Dr. David A. Robinson
Professor and Chair, Department of Geography
New Jersey State Climatologist
Rutgers University
54 Joyce Kilmer Avenue
Piscataway, NJ 08854-8054
Telephone: 732-445-4741
Fax: 732-445-0006

Technical Contact:

NSIDC User Services
National Snow and Ice Data Center
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services

2.Detailed Data Description:


The data are in ASCII text format.

File Size:

8 Kb

Spatial Coverage:

The data set contains reconstructions of snow cover extent for North America.

Temporal Coverage and Resolution:

The data span ranges from December 1900 to March 1993 and contains time series of reconstructed monthly snow extent.

Parameter or Variable:

The data consist of reconstructed monthly snow extent values, standard errors, and observed values (when available).

Sample Data Record:

Year Nov-R Nov-SE Nov-Obs Dec-R Dec-SE Dec-Obs Jan-R Jan-SE Jan-Obs Feb-R Feb-SE Feb-Obs Mar-R Mar-SE Mar-Obs
1910 10.42 0.749 13.60 0.654 14.86 0.595 14.35 0.396 12.54 0.496
1911 11.72 0.749 13.87 0.654 14.34 0.595 14.25 0.396 12.64 0.496
1912 10.25 0.749 13.55 0.654 15.10 0.595 14.68 0.396 14.53 0.496

Abbreviations Key:
R: Reconstructed values
SE: Standard errors of the reconstructions; can be used as confidence limits
Obs: Observed values upon which the reconstructions are based

All values are in units 106km2

3.Data Access and Tools:

Data Access:

Data are available via FTP.

Related Data Collections:

Reconstructed North American, Eurasian, and Northern Hemisphere Snow Cover Extent, 1900-1997

Please see Snow Data Sites for additional snow data.

4.Data Acquisition and Processing:

The investigator generated a time series of reconstructed monthly snow cover extent based on linear regressions between station-based snow observations (from the Cooperative Weather Observer Program) and remotely sensed visible-band imagery (from the NOAA polar orbiting series of satellites). Additionally, the data set includes standard errors of snow cover estimates and the observed values upon which the regressions were based.

Frei et al. (1999) and Frei and Robinson (1999) describe the reconstruction method, along with its advantages and disadvantages.

5.References and Related Publications:

Brown, R. 2002. Reconstructed North American, Eurasian, and Northern Hemisphere snow extent, 1915-1997. Boulder, CO: National Snow and Ice Data Center. Digital media.

Frei, A. and D. A. Robinson. 1999. Northern Hemisphere snow extent: regional variability 1972-1994. International Journal of Climatology 19: 1535-1560.

Frei, A., D. A. Robinson and M. G. Hughes. 1999. North American snow extent: 1900-1994. International Journal of Climatology 19: 1517-1534.

Robinson, D. A. 1993. Historical daily climatic data for the United States. Proceedings of the Eighth Conference on Applied Climatology. Anaheim, CA. American Meteorological Society: 264-269.

Robinson, D. A., K. F. Dewey and R. R. J. Heim. 1993. Global snow cover monitoring: an update. Bulletin of the American Meteorological Society 74(9): 1689-1696.

Robinson, D. A. and A. Frei. 1999. Seasonal variability of Northern Hemisphere snow extent using visible satellite data. Professional Geographer 52(2): 307-315.

6.Document Information:

Document Creation Date:

17 October 2002

Document Revision Date:

Document Review Date:

Document URL: