As the long, cold and dark part of the year departs, break-up of Alaska’s rivers is getting underway.  The National Weather Service expects this that year, it could trend toward more of a mechanical event, with ice jams and flooding being more likely in some parts of the state.  NWS Hydrologist Crane Johnson presented the Alaska-Pacific River Forecast Center’s outlook at a webinar hosted by the Alaska Center for Climate Assessment and Policy (ACCAP).  Pilots are encouraged to consider participating in the River Watch Program this year,  sharing photos and/or pilot reports of ice conditions as we fly along the rivers between mid-April and perhaps into early June, to help monitor this situation.

Forecast for 2021
Factors that influence the nature of river break-up include thickness and areal extent of ice that formed over the winter, the quantity of the snowpack, and spring weather.   Crane was joined by ACCAP Climatologist Rick Thoman, who summarized the temperature and precipitation over the past winter and then looked ahead at the forecasts for the weeks ahead.  Based on this data, we should expect more of a mechanical break-up with the ice jams and associated flooding this year, as opposed to a gentle thermal break-up where ice largely melts in place and does not provide much resistance to the increased river flow associated with melting snows.  For more details on the processes in play, and the specifics of what areas are most at risk, I encourage you to watch the recording of the webinar, presented on April 13.

 

Breakups can vary in intensity depending on winter conditions, and how fast warming conditions develop in the spring. Based on existing conditions and forecasts, this season is expected to have more mechanical characteristics.

 Areas at Risk
Looking across the state, some regions are more at risk than others.  While ice thickness and snow cover are known to some extent, the remaining wild card is the temperature in the weeks ahead.  Based on forecast data to date, the break-up outlook map depicts an above average potential for flooding across the interior along the Yukon, Tanana and Kuskokwim drainages, as well as in the Copper River drainage and in the southeast panhandle.

The Spring Flood potential will be updated periodically. The current version will be found at: https://www.weather.gov/aprfc/floodpotential.

Historical Distribution of Ice Jams
While attention is often focused on the larger rivers, Crane also presented a map of the historic distribution of ice jams across the state.  It shows that they have occurred in more locations than just the major rivers.  Given this widespread distribution of possible locations for ice jams, observations from pilots can be particularly helpful to the River Forecast Center in monitoring break-up.

Ice jams can occur on a wide variety of rivers across the state. Consider flying segments of the smaller rivers to look for ice jams and related flooding.

What can Pilots Do?
If you are willing to devote some flight time to help the National Weather Service monitor break up this Spring, consider participating in the River Watch Program.  Initially designed to use Pilot Reports as the primary mechanism for reporting ice or flooding conditions, it now more commonly uses pictures taken with a smart phone (preferably with GPS turned on) of river conditions.  Email them to the River Forecast Office after getting back on the ground.

Information about the program, what to look for, and how to communicate results, is available on the River Watch page.  As the season progresses, NWS will update their breakup status map and indicate areas they are specifically interested in learning about–so check back periodically for updates.  Please keep in mind that not all communities are open to outside visitors; so, check the state’s Safe Travel site for local restrictions, before you plan your flights.

River Watch image on the Yukon River using the Theodolite App to capture location direction and altitude.

River Watch is a way for general aviation to contribute to the public good, while clearing out the cobwebs if you didn’t fly much over the winter.  Check out the details on the River Watch website and consider this a good reason to get airborne.  And while you are capturing river details with a smart phone, take time to file a Pilot Report or two with Flight Service when you are in locations that don’t have reported weather. Your PIREPs are appreciated!