Data Set ID:

Nenana Ice Classic: Tanana River Ice Annual Breakup Dates, Version 2

The Tanana river in the Interior of Alaska usually freezes over during October and November. The ice continues to grow throughout the winter accumulating an average maximum thickness of about 110 cm, depending upon winter weather conditions.

The Nenana Ice Classic competition began in 1917 when railroad engineers bet a total of 800 dollars, winner takes all, guessing the exact time (month, day, hour, minute) ice on the Tanana River would break up. Each year since then, Alaska residents have guessed at the timing of the river breakup. A tripod, connected to an on-shore clock with a string, is planted in two feet of river ice during river freeze-up in October or November. The following spring, the clock automatically stops when the tripod moves as the ice breaks up. The time on the clock is used as the river ice breakup time.

Many factors influence the river ice breakup, such as air temperature, ice thickness, snow cover, wind, water temperature, and depth of water below the ice. Generally, the Tanana river ice breaks up in late April or early May (historically, April 20 to May 20). The time series of Tanana river ice breakup dates can be used to indicate climate change in the region.

This is the most recent version of these data.

Version Summary:

This version upgrade includes:
- a change in data file format to CSV
- a temporal update
- corrections in the time format

BASIC Level of Service

Data: Data integrity verified

Documentation: Key metadata and links to supporting documentation available

User Support: Assistance with data access and basic data usage

See All Level of Service Details

Data Format(s):
  • ASCII Text
Spatial Coverage:
N: 64.565, 
S: 64.565, 
E: -149.093, 
W: -149.093
Spatial Resolution:Not applicableSensor(s):CLOCKS
Temporal Coverage:
  • 1 April 1917
Temporal Resolution1 yearMetadata XML:View Metadata Record
Data Contributor(s):Nenana Ice Classic, . Edited by W. N. Meier and C. F. Dewes.

Geographic Coverage

Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Nenana Ice Classic, . Edited by W. N. Meier and C. F. Dewes. 2020. Nenana Ice Classic: Tanana River Ice Annual Breakup Dates, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: [Date Accessed].
24 July 2020
Last modified: 
11 August 2020

Data Description


The parameter provided by this data set is the date and time of when the ice in the Tanana River, at the town of Nenana, AK, broke up each spring. It is given in both standard date and time units and also in decimal day of the year, which represents both the day of the year and time of the day in the same record.

File Information

Format and File Contents

Data are provided in CSV format, in a single file where each row describes a year's ice breakup date and time. The five columns in the file indicate: (1) the year, (2) the decimal day of the year, (3) the month, (4) the day, and (5) the time at which the ice breakup occurred. 

Spatial Information

The time series is representative of a single point on the Tanana River in Alaska, with coordinates 64.565 N and 149.093 W. 

Temporal Information


Data covers from 1917 to present (updated annually)



Figure 1. Time series of the Tanana River ice break-up dates for the period 1917-2020. The blue line represents the annual river ice break-up dates in day of year (left vertical axis), with the equivalent calendar date (illustrative of a leap year; subtract one day for non-leap years) shown on the right vertical axis. The red line illustrates the quasi-decadal trend, represented here by a 9-year moving average. The black line represents the mean river ice break-up date, which in this period is May 4.

Version History

Table 1. Version history
Version Date Version Changes
Version 1 August 1998 Initial release
Version 2 August 2020 Data file format was changed to CSV; errors in the computation of the fractional time of day were corrected


Official Nenana Ice Classic web site

No technical references available for this data set.

How To

V0 Programmatic Data Access Guide
Data from the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) can be accessed directly from our HTTPS file system. We provide basic command line Wget and curl instructions for HTTPS file system downloads below. For questions about programmatic access to NSIDC... read more