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000
FGAK78 PACR 052117 CCA
ESFAK

Hydrologic Outlook
NWS Alaska Pacific River Forecast Center Anchorage AK
1PM AKDT FRI APR 5 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_20240405.pdf



...SPRING BREAKUP OUTLOOK FOR ALASKA...


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

April 1 ice thickness data across the state are near normal. Recent
snowpack measurements show normal to above normal snowpack at most
locations across interior Alaska. Climate outlooks are indicating
temperatures to remain colder than normal across most of interior
Alaska through mid April.


...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: Above 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 March and early April measurements
indicate that ice thickness is near normal across the state.
Observations from the Interior range from 85%-110% of normal, with
observations along the mid-Yukon River approximately 85% normal.
However, dense jumble ice has been observed on the 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). Observers on the Kuskokwim River have
reported normal to slightly below normal ice thicknesses between
Aniak and Bethel, with March reports indicating that river ice has
begun to deteriorate, and/or soften in some locations.


...Freezing Degree Days...

Cumulative freezing degree days (FDD) as of April 1, which can serve
as a proxy for river ice thickness, are near normal across most of
Alaska including Southcentral and across interior Alaska. Colder
than normal conditions were observed across coastal sites along the
Gulf of Alaska (Homer to Sitka), where FDD was reported to be 120%
to 200% of normal.


...Snowpack...

The April 1st Naturual Resources Conservation Service (NRCS)
analysis has not been released yet. The March 1 analysis indicates
above normal snow for the majority of the state and the preliminary
April 1 data indicates the Alaska snowpack percent of normal likely
has not changed significantly.

The Yukon Basin end of March NRCS analysis combined with the early
March Yukon Canada snowpack analysis indicate normal to above normal
snowpack in the basin. The Porcupine and Fortymile basins are
reporting well above normal snowpack approaching 150%.

The Northslope snowpack is likely normal to below normal based on
limited measurements.

The upper Kuskokwim River basin is below normal however the number
of reported measurements is very small. Recent observations from
observers at various communities indicate above normal snowpack
other climate analyses also indicate likely above normal snowpack.

In Southcentral Alaska, the snowpack in the Copper Basin is notably
above normal. All monitoring sites in the basin are reporting above-
normal snowpack levels. Notably, eight sites in the basin rank
within the top five of historical records for snowpack levels, with
three sites reporting record highs. However, despite this above-
average snowpack, it`s worth noting that the basin`s average
snowpack remains lower than the levels observed in 2022 (175-200%)
and 2023 (160-180%). Glennallen experienced flooding both of those
years. The Susitna Basin is reporting above normal, with the
snowiest locations in the eastern headwaters, bordering the Copper
Basin.

The next NRCS statewide snowpack summary is expected after the first
week of April.


...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.

NOAA’s Climate Prediction Center April 4 outlooks favor normal to
colder than normal temperatures through the third week in April.
This outlook would indicate an increased liklihood of a fairly rapid
warm up over interior Alaska in late April as temperatures are
forecast to warm toward normal. The April-May-June forecast is for
above normal temperatures across Alaska.


The next Spring Breakup Outlook will be published April 14, 2024.


$$
DPS