Expires:No;;032230 SRAK48 PACR 111723 CCA RVAAK Alaska Spring Breakup Summary NWS Alaska Pacific River Forecast Center Anchorage 1000 AM AKDT SAT MAY 11 2024 The Breakup Summary is issued seasonally after breakup begins. The Alaska-Pacific River Forecast Center is updating the format of its breakup outlook and summary products. The new experimental format proposes to move to a more graphical presentation, away from the historically text-based product below.  The likelihood of flooding from snowmelt and/or ice jams is initially calculated based on the flood frequency for the current 2000 to 2021 historical record and adjusted to reflect current conditions. The experimental graphical format Alaska Spring Breakup Outlook products are posted to the Alaska-Pacific River Forecast Center website at: www.weather.gov/aprfc/breakupProducts A direct link to the latest graphical product is: www.weather.gov/media/aprfc/BreakupProducts/ESFAK_ACR_20240510.pdf ..Spring Breakup Summary for Alaska... Current Conditions * On the Kuskokwim River several ice jams downriver from Kweethluk caused extensive flooding over the past few days. Currently an ice jam has formed just downriver from Napakiak and flooding is occurring at Napakiak. Expect the lower Kuskokwim River ice to flush out to the mouth over the next couple of days. * On the Yukon River cooler temperatures this breakup season have kept snowmelt breakup gradual. Cooler temperatures are expected to continue, with this year leaning to a more thermal breakup on the Yukon River. * Upper Yukon River- the main breakup front is a jam 12 miles upstream of Circle. Overall water levels are low and the ice front has been moving slowly. * Middle and Lower Yukon - No changes yet, anticipate timing to be close to normal. * The Tanana River has been ice free for about a week. The 2024 spring breakup is trending more towards a thermal* breakup across the much of Alaska. In the Eastern Interior late April temperatures were warm, helping to deplete low elevation snowpack and degrade river ice across the middle and upper Tanana River as well as portions of the Upper Yukon River. Across the western part of the state, including the middle/lower Yukon River, breakup has been slow because temperatures are still gradually easing out of winter. *The two generalized types of river ice breakup are dynamic (or mechanical) and thermal. A dynamic breakup is characterized by cold early spring air temperatures followed by rapid warming, and can be compounded by above average headwater snowpack and river ice thicknesses, and generally moves the breakup ice front downstream in a somewhat linear fashion. Ice jam flooding occurs more often during a dynamic breakup. A thermal breakup occurs from gradually warming air temperatures, where the ice simply rots in place. Thermal breakups does not mean no flooding, ice jams do occur but they are commonly less severe. ...Forecast Conditions... * Yukon - Expect continued decay and likely thermal breakup for communities on the midde Yukon over next few days. * Buckland - expect the river ice to go out during next few days * Kobuk - expect the river ice to go out during the next few days ...Climate Outlook... The most important factor determining the severity of ice jam breakup remains weather immediately prior to and during breakup. Dynamic breakups, with the high potential for ice jam flooding typically require an abrupt warm up in temperature. In the near term, temperatures in the interior are close to climate normals, with highs in the 50s and lows in the 30s. In Bethel, highs will be in the 40s, and lows in the 30s. The relatively normal temperatures and slow warm up are good indicators of trending towards a thermal breakup. The Climate Prediction Center temperature outlook for mid May indicates an increased chance of cooler than normal temperatures for southwest Alaska and normal temperatures for the eastern interior and north slope. Cooler temperatures in mid May have the greatest impact on the Lower Yukon River; the key will be where the ice jam front comes into contact with stronger downstream ice. ...Spring Breakup Timing... Timing of river breakup considers all previously described variables and relates it to the historical median breakup date for individual locations. Based on this evaluation, breakup is expected to be 0-2 days early in the eastern half of Alaska. Western and Southwest Alaska are forecast to break up 0-2 days later, although some locations may trend towards median. The North Slope is expected to break up closer to its median date. ...Flood Potential... Please refer to the Flood Potential Map at the APRFC website for timing and flood potential details at: https://www.weather.gov/aprfc/floodpotential Tables in the Experimental Product give an estimation of snowmelt runoff volume, flood potential, and forecast breakup date range for various locations across the state. To view the tables and for additional information please visit: https://www.weather.gov/aprfc/breakupProducts The next Spring Breakup Outlook will be published May 17, 2024. $$ DS/MO