Flood Potential Outlook
Issued by NWS
Issued by NWS
010 FGAK78 PACR 151825 RRA ESFAK Hydrologic Outlook NWS Alaska Pacific River Forecast Center Anchorage AK 1000 AM AKDT FRI MAR 15 2024 ...UPDATED BREAKUP OUTLOOKISSUED USING THE EXPERIMENTAL GRAPHICAL FORMAT... An updated Alaska Spring Breakup Outlook has been posted to our website using the experimental graphical format. The Alaska-Pacific River Forecast Center is updating the format of breakup outlook and summary products. The new experimental format proposes to move to a more graphical format away from the text based product below. A list of the latest breakup products issued by the Alaska Pacific- River Forecast Center using the new format is at: www.weather.gov/aprfc/breakupProducts A direct link to the latest graphical product is: www.weather.gov/media/aprfc/BreakupProducts/ESF_ACR_20240315.pdf ...SPRING BREAKUP OUTLOOK FOR ALASKA... ...Statewide Flood Potential Overview... The outlook for Alaska spring ice breakup and snowmelt flood potential is currently rated as normal for the majority of the state. The spring breakup flood potential for major rivers in Alaska: ..Yukon River: Normal ..Koyukuk River: Normal ..Kuskokwim River: Normal ..Tanana and Chena Rivers: Normal ..Copper Basin Rivers: Above Normal ..Susitna River: Normal ..North Slope Rivers: Normal This outlook is based on observed snowpack, ice thickness reports, and seasonal temperature outlooks. The term normal is defined as being at or near the climatological value, which is typically defined over a 30-year period of record. ...River Ice Observations... River ice observations are available for a limited number of observing sites in Alaska. Late February and early March measurements indicate that ice thickness is near-to-below normal across the State. Observations from the Interior range from 65%-95% of normal, with observations along the mid-Yukon River approximately 85% normal. Observers on the Kuskokwim River reported normal ice thickness. No freeze-up jams or mid-winter breakups were reported across the Yukon and Kuskokwim River basins. Cumulative freezing degree days (FDD), which can serve as a proxy for river ice thickness, are near normal across most of Alaska due to fairly mild winter air temperatures. Colder conditions were observed across coastal sites along the Gulf of Alaska (Homer to Sitka), where FDD was reported to be 110% to 200% of normal. Normal FDD conditions have been observed across Southcentral and Copper River Valley, 105% and 100% of normal, respectively. The West Coast, Interior, and North Slope observed near normal FDD, ranging from 85% to 100% of normal. ...Snowpack... Analysis of the March 1st snowpack by the Natural Resources Conservation Service (NRCS) indicates a variable snowpack; but generally the statewide snowpack is above normal for the majority of the state. The snowpack for the Upper Yukon (largely in Canada) is reporting near normal. A handful of sites in the perimeter of the basin are 100-125% of normal, but the vast majority are 60-90% of normal, bringing the basin total to 92% of normal. The Central Yukon Basin, which includes Eagle, Circle, and Ft Yukon is above normal, at 133%. The Porcupine and the Fortymile Rivers are reporting well above normal, with 157 and 137% or normal respectively. The Tanana Basin, which includes Fairbanks and Delta Junction, is near normal at 109% of normal. The Koyukuk Basin has a variable snowpack; along the Dalton Highway it is well below normal, extending to near period-of- record maximum near the Yukon River; overall the basin is 125% of normal. The Lower Yukon Basin, which includes the villages of Tanana, Ruby, Galena, and Anvik, have stations reporting between 150 and 200% of normal at the lower elevations and closer to normal at the higher elevations. The Kuskokwim Basin has a normal to above normal snowpack. Telaquana Lake in the far southeast Kuskokwim headwaters is below normal due to a mid February warm up; McGrath avoided the warm up and is reporting a near normal snowpack. Lower in the basin, between Aniak and Bethel, observers are reporting above normal snowpack. For the Arctic, the three stations along the Dalton Highway are reporting below normal snowpack. In Southcentral Alaska, the Copper Basin has a well above normal snowpack, even greater than in 2022 and 2023 which flooded Glennallen. Every station in the basin is reading above normal, with four period-of-record maximums. The Susitna Basin is reporting 122% of normal, with the snowiest locations in the eastern headwaters, bordering the Copper Basin. Stations in the Kenai Basin are reporting generally above normal with the highest returns in the Kenai River specifically. The basin-wide snowpack can be approximated at 121% of normal. ...Climate Outlook... The most important factor determining the severity of ice breakup remains the weather during April and May. Dynamic breakups, with a high potential for ice jam flooding, typically require cooler than normal temperatures in early April followed by an abrupt transition to warm, summer-like temperatures in late April to early May. NOAAs Climate Prediction Center outlook through early April favors above normal temperatures across most of Alaska, except for the Northwest Coast and the western North Slope, where equal chances of above and below normal temperatures are possible. In the Upper Yukon, as well as the Copper and Susitna Basins, the CPC guidance suggests a 60-70% chance of above normal temperatures. The longer, 3- month outlook, which includes March, April, and May indicates increased chances of above normal temperatures across all of Alaska. This temperature pattern would reduce ice jam related flood risk along the Kuskokwim and Yukon Rivers. These larger rivers are westward flowing and warmer temperatures on the west coast would result in ice degradation prior to the arrival of snowmelt runoff, decreasing the chances for a dynamic breakup. The next Breakup Outlook update will be published March 22, 2024. $$ JSO