Dear Arctic Science and Sea Ice Community,
The Sea Ice Prediction Network (SIPN) invites you to contribute to the September 2025 Sea Ice Outlook (SIO)—a collaborative, community-driven effort to improve and compare seasonal sea ice forecasts. Whether you are a returning contributor or new to the Outlook, your input is highly valued. Please share this call with colleagues, collaborators, or research groups who may be interested in participating.
Questions? Contact the SIO team at sio2025@arcus.org
Call for Contributions: September 2025 Sea Ice Outlook (Based on May, June, July, and August Data)
Submission Deadline: 6:00 p.m. AKDT | Tuesday, 23 September 2025
The Sea Ice Outlook (SIO) offers a platform for researchers and forecasters to share predictions of September Arctic sea-ice extent and related variables. Following each month's collection of contributions, key visualizations (including pan-Arctic sea ice forecast figures) will be published by month on the SIO website. A Post-Season Report, focusing on June-September forecast accuracy and performance compared to the observed minimum, is planned for release after the melt season.
The 2025 SIO is supported through in-kind contributions from the University of Washington, NSIDC, University of Alaska Fairbanks, and ARCUS.
The 2025 SIO solicitation is the same as 2024—contributors are asked to submit a new outlook for each month of the melt season (June-September). No submitted outlooks will be automatically carried forward from one month to the next. For example, please do not submit outlooks developed in July (based on June and July data only) to the August SIO. (See the tentative schedule linked below.)
Additionally, we encourage submissions to the associated effort of the Sea Ice Drift Forecast Experiment (SIDFEx); see details below under "Associated Effort – Sea Ice Drift Forecast Experiment."
SEPTEMBER SUBMISSION DEADLINE: 6:00 p.m. AKDT, Tuesday 23 September 2025
Contributions received after the deadline may not be fully incorporated into the Outlook figures.
Questions, including how to submit contributions that may not fit into one of the requested formats below, may be directed to the SIO team at sio2025@arcus.org.
Sea Ice Outlook data resources are available via the National Snow and Ice Data Center (NSIDC) SIPN Data Set webpage.
The 2025 SIO Solicitation Requests:
Outlooks for pan-Arctic, pan-Antarctic, and Alaskan regional September monthly mean sea-ice extent, related uncertainty/probability estimates, and the optional submissions of sea-ice extent anomaly forecasts. We particularly encourage submissions for the Alaska region (i.e., Bering, Chukchi, and Beaufort seas).
Full Field of Sea Ice Forecasts:
Estimates of Sea Ice Probability (SIP), defined as the fraction of ensemble members in an ensemble forecast with September ice concentration in excess of 15%.
Estimates of Ice-Free Dates (IFD), defined as the first day that Sea Ice Concentration (SIC) drops below 15% ('IFD15'). A second metric we invite is the IFD calculated for an 80% SIC threshold ('IFD80').
For August and September only: estimates of Ice Advance Dates (IAD), defined as the first date (quantified as day of year) in the freeze up season (i.e., after the summer minimum) at which ice concentration first increases over 15% ('IAD15') and over 80% ('IAD80').
Spatial fields of forecast's initial conditions, particularly sea ice concentration and sea ice thickness or ice thickness distribution, with the date of initialization documented. If forecasts are produced from multiple initializations, these could be the mean fields across your initializations or you can include each single initialization.
Supplemental materials, including PDFs of any additional figures and/or text files,
Note: All participants whose methods provide information at the regional scale are again encouraged to provide full spatial fields. These submissions will allow organizers to compute metrics such as sea ice probability and first ice-free day for contributors, as well as additional regional analysis for the Sea Ice Outlook. (See submission instructions below.)
2025 Submission Instructions
Instructions for Submitting Pan-Arctic, Pan-Antarctic, and Alaska Regional Outlooks
Required core information for pan-Arctic Outlook projections using dynamical model, statistical, heuristic, and mixed methods. To be consistent with observations from the NSIDC Sea Ice Index extent, compute the total extent (sum of cell areas >15%) for each day and then average the extents from each of the days in the month into a monthly average extent.
Information for pan-Antarctic and/or Alaska regional sea ice extent projections using dynamical model, statistical, heuristic, and mixed methods. (Please see details below under “Additional Instructions for Submitting an Alaskan Regional Outlook").
Additional Outlook report details, including discussions and details related to uncertainties/probabilities. (Uncertainty values are solicited for the pan-Arctic only).
Executive summaries describing in plain words your Outlook, contributing factors, and your methodology.
Contributors who do not have access to the Google Form or a Google account should send their submission materials and a PDF of the submission form via email to sio2025@arcus.org.
Additional Instructions for Submitting an Alaskan Regional Outlook
Please submit a total extent for the Alaskan region, defined here as the combination of the Bering, Chukchi, and Beaufort seas. If possible, use the definition from the NSIDC Arctic sea ice regional graphs and time series from the mask below, which is on the 25 km by 25 km polar stereographic projection used for the passive microwave satellite data.
The mask is provided as a NetCDF file here: NSIDC Regional Mask (NC - 2 MB).
Also tell us the maximum possible ice extent if every ocean cell in your Alaska region were ice covered. For example, if your model uses exactly the same grid as the satellite data, the area would be 4.00 x 106 km2. The maximum possible extent is probably much larger than your actual Alaskan Regional Outlook. Be sure to exclude land and islands.
Finally, with your entry, please include how you defined the Alaskan region: either say NSIDC definition, or if you must use your own definition, describe it.
Enter your submission via the Google-based submission form under the "Outlook Prediction" header.
For questions about the format of this request, please contact the SIO team (sio2025@arcus.org).
Note: If you skip this step but provide full fields, we'll compute an Alaskan regional outlook for you.
Instructions for Submitting Full Field of Sea Ice Forecasts
To contribute fields of SIP, IFD, IAD (or the daily sea ice concentration fields, from which we will calculate the SIP, IFD and IAD for you) and initial conditions, please upload to the SIPN data server using the same username and password of past years. If you are a new contributor of these fields and need to set up a new username and password, or have any queries on how to upload the data, please contact Ed Blanchard at edwardbw@uw.edu.
For examples and further information on the SIP, IFD, and IAD metrics, see Metrics for the Sea Ice Outlook.
Instructions for Submitting Pan-Arctic Sea Ice Extent Anomalies (optional)
This is an optional submission and it is recognized that not all SIO contributors will be able to provide anomaly forecasts. The request is motivated by the large spread in SIO predictions of mean September sea-ice extent. Some of this spread likely reflects inter-model biases, i.e., some models consistently overestimate ice extent while others underestimate it (relative to observations). The goal of this activity is to eliminate this source of inter-model prediction spread. The long-term mean is not a well-defined concept in a rapidly changing Arctic.
The pan-Arctic sea ice extent anomaly is the departure of the contributors' September extent Outlook relative to the contributors' baseline trend, e.g., the trend in historical observations, model hindcasts, etc.
To calculate a pan-Arctic sea ice extent anomaly:
Calculate the multi-year linear trend (slope) of September-mean extent from your baseline period. The linear trend will be different for each contributor due to inter-method/model biases.
Extrapolate the linear trend to calculate an extrapolated September 2025 extent value.
Calculate the extent anomaly value by subtracting the September 2025 Outlook extent from the extrapolated trend September 2025 value.
Instructions for Submitting Supplemental Material (optional)
Send supplemental material as an e-mail attachment sent to sio2025@arcus.org.
Please provide supplemental material as a single PDF (less than 20 MB).
Clearly identify your contribution by using the same email address and group name as provided on the submission form so we can link it to your submission.
Examples of supplement materials include: relevant figures, imagery, references, or further information about your methods.
Associated Effort – Sea Ice Drift Forecast Experiment
Contributions are again also invited to the Sea Ice Drift Forecast Experiment (SIDFEx), a community effort to collect and analyze sea ice drift forecasts at lead times from days to a year. The forecasts target drifting sea-ice buoys. SIDFEx is aligned with the Sea Ice Outlook such that modeling groups contributing to the Sea Ice Outlook can contribute to SIDFEx relatively easily by computing trajectories for Lagrangian tracers. Results from the last years have been described briefly in the Sea Ice Outlook Post-Season Reports. This time, we also invite suggestions for buoys or other easily tracked targets such as ships or field experiment sites to be added to the list of SIDFEx targets.
For further Information, see the SIDFEx Homepage or email the SIDFEx team (sidfex@polarprediction.net).
For details on the design of SIDFEx and how to contribute drift forecasts, please download the following document.
Background and Guidelines for SIDFEx Contributions.
REMAINING 2025 SIO SCHEDULE
SEPTEMBER: (Based on May, June, July, and August data)
- 9 September 2025 (Tuesday): Call for Contributions to September Report
- 23 September 2025 (Tuesday): Deadline for September Contributions
POST-SEASON REPORT
- Focus will be on the performance of Outlooks as compared to sea-ice minimum.
- Additional discussion and analysis of factors driving sea-ice extent during the 2025 melt season
- Developed following the conclusion of the retreat season.