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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