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ESFAK 



Hydrologic Outlook 

NWS Alaska Pacific River Forecast Center Anchorage AK 

440PM AKDT FRI APR 19 2024





...UPDATED BREAKUP OUTLOOK ISSUED USING AN EXPERIMENTAL GRAPHICAL 

FORMAT...





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 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_20240419.pdf 







...Spring Breakup and Flood Potential Outlook for Alaska... 



Across Alaska, the 2024 spring breakup is shaping up to be dynamic*. 

Temperatures are forecasted to remain below normal through the end 

of April, particularly for the western half of the state, and a 

robust snowpack persists across northeast and western Alaska. 

However, while we anticipate a dynamic breakup in some areas this 

year, the conditions aren't as favorable as they were at the 

beginning of the 2023 historic breakup season, which was marked by 

numerous significant ice jams and snowmelt floods across the 

Interior. If air temperatures remain cold through the remainder of 

April and into early May, the chances increase for a dynamic breakup 

and localized flooding.



*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 usually. 

Thermal breakups commonly result in fewer and less severe ice jams.





...Updates to the previous Spring Breakup Outlook... 



Ice thickness across Alaska remains near normal through April. April 

1 statewide snow summary showed well-above normal snowpack for the 

North Slope, Porcupine, Copper, Lower Yukon, and Kuskokwim river 

basins. Recent aerial snowpack measurements show very high snow 

amounts in the Nushagak Hills near Dillingham and the Holitna River 

near Sleetmute basins, as well as in the lower Kuskokwim River below 

Aniak. Normal to slightly below normal snowpack was observed in the 

Upper Yukon and Tanana river valleys. Climate outlooks favor 

elevated chances of above normal temperatures in central and eastern 

Alaska and equal chances of above, below, and/or normal temperatures 

in western Alaska through the first half of May. 





...Spring Breakup Flood Potential along major rivers in Alaska... 



Spring breakup village flood potential considers the climate 

outlook, snowpack, ice thickness and condition, historical 

likelihood of flooding and flood severity, and community knowledge. 

Village flood potential is reassessed continually as outlooks change 

and breakup season progresses. Please see most recent Experimental 

Product for figure at www.weather.gov/media/aprfc/BreakupProducts/.





...River Ice Observations...



April 1st river ice observations are available for a limited number 

of sites in Alaska. Late March through mid- April measurements 

indicate that ice thicknesses are near normal across the state. 

Observations across interior Alaska range from 81%-111% of normal. 

However, dense jumble ice has been observed on the middle Yukon 

River between Rampart and Tanana. Recent UAF Fresh Eyes On Ice team 

(FEOI) reconnaissance confirmed that ice this year (2024) along the 

middle Yukon and Tanana River was on average thicker than last year 

(2023). Yukon River ice thickness at Eagle appears to be thicker 

than the past two winters (2022-2023), with river observers noting 

significant jumbled ice in the vicinity. Observers on the Kuskokwim 

River reported normal to slightly below normal ice thicknesses 

between Aniak and Bethel, with recent reports indicating that river 

ice has begun to deteriorate, and/or soften in some locations. Ice 

thicknesses along the Kuskokwim are, on average, 20% less than this 

time last year. No freeze-up jams or mid-winter breakups were 

reported in the Yukon or Kuskokwim river basins this winter.





...Freezing Degree Days...



Cumulative freezing degree days (FDD), which can serve as a proxy 

for river ice thickness, are near normal across most of Alaska. 

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. Near normal FDD conditions have been observed across 

Southcentral and Copper River Valley. The West Coast, Interior, and 

North Slope observed near to below normal FDD, ranging from 83% to 

101% of normal.  





...Snowpack... 



April 1 Natural Resources Conservation Service (NRCS) snowpack 

analysis indicates an above average snowpack for the majority of the 

state. 



Although snowpack observations are limited, North Slope winter 

precipitation is well-above average indicating likely above average 

snowpack north of the Brooks Range. In fact, year-to-date 

precipitation at Utqiaġvik Airport and Prudhoe Bay are the highest 

on record. The record at Utqiaġvik goes back eighty-nine years.



In the northeastern region of Alaska, the Porcupine basin has a 

measured snowpack well-above average, with Old Crow village in the 

northern Yukon Territory recording its highest snowpack levels in 

over four decades of monitoring. However, as one moves towards the 

southern half of the Yukon Territory, snowpack conditions vary, with 

areas from Whitehorse to Mayo experiencing average to below-average 

levels. Meanwhile, the Upper Yukon basin spanning from Dawson to 

Fort Yukon, as well as the Fortymile basin, exhibit snowpack levels 

well-above average, measuring around 130% of the 1991-2020 normal.



Further down the Yukon, snowpack remains near average until reaching 

the lower Yukon, where the snowpack is ~120-135% of normal. The 

Tanana and Upper Kuskokwim basins snowpack ranges from average to 

slightly below average. However, in the middle to lower Kuskokwim 

snowpack levels are significantly higher, reaching approximately 150-

170% of the April 1 average (1991-2020), as indicated by ERA5 model 

analysis. This assessment is corroborated by anecdotal reports and 

in-situ observations, notably in Bethel, which has a measured record 

high April 1 snow depth based on 100 years of record.



In Southcentral Alaska, the snowpack in the Copper basin stands at 

around 140% of the April 1 average. Monitoring sites throughout the 

basin are consistently reporting higher-than-average snowpack. 

Notably, four sites within the basin rank within the top three of 

historical records for snowpack levels as of April 1. However, it's 

important to note that despite this above-average snowpack, the 

basin's snowpack remains lower than the levels observed in 2022 

(180%) and 2023 (160%), both of which resulted in flooding in 

Glennallen.



Across the rest of Southcentral Alaska, the Susitna basin is 

reporting normal snowpack, while the Cook Inlet watershed and Kenai 

Peninsula have an above-average snowpack.



Snowpack depth and extent is used to estimate the snowmelt runoff 

potential across Alaska. 



In summary, the state's snowpack is generally above average, with 

anomalies increasing from average in the east to above average in 

the west. A well-above average snowpack is noted in the Porcupine, 

Yukon, and Lower Kuskokwim, as well as the Copper basins. Although 

above average this year, snowpack across most of the interior is 

notably less than the previous two years.



The next NRCS Statewide Snowpack Summary is expected after the first 

week of May.





...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.



The amplified pattern across mainland Alaska is expected to quickly 

transition from enhanced ridging to moderate troughing over the 

eastern Bering Sea and Arctic Ocean through the end of April. Under 

this pattern, the Climate Prediction Center’s climate outlook for 

the 8-14 day range favors better chances for below normal 

temperatures for the western half of the state. Meanwhile over 

eastern Alaska, persistent ridging will yield higher chances for 

above normal temperatures, primarily along the Yukon border.



The week 3-4 timeframe continues to feature better than average 

chances for above normal temperatures for much of eastern Alaska. 

For interior and western Alaska, equal chances of above, below, 

and/or normal temperatures are predicted. It should be noted that 

there is considerable uncertainty during this time period leading to 

low confidence in any solution.



Looking ahead at the longer, 3-month outlook, which includes May, 

June, and July, there's an elevated probability (40-60% chance) of 

above-normal temperatures across the eastern two-thirds of Alaska.





...Spring Breakup Timing...



Timing of river breakup takes into account 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 later in the eastern half of Alaska, although some 

locations may break up early. Western and Southwest Alaska are 

forecast to break up 1-4 days later. The North Slope is expected to 

break up closer to its median date.





...Flood Potential...



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. 



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. 



Median breakup dates are for the period 1980 through 2023 and are 

calculated for locations with at least 5 years of data. 



Forecast breakup timing is expressed as a range based on snowmelt 

runoff volume and flood potential. Locations where breakup has 

already occurred are identified with two asterisks preceding a 

single date; for example Kuskokwim River at Nikolai breakup occurred 

on April 16, 2024 (**4/16).





Please refer to the Flood Potential Map at the APRFC website for 

timing and flood potential details at: 

https://www.weather.gov/aprfc/floodpotential 



For additional information please visit: 

https://www.weather.gov/aprfc/breakupProducts

  

The next Spring Breakup Outlook will be published April 26, 2024.  





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JSO/MSO