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000
FGAK78 PACR 292248 CCA
ESFAK

Hydrologic Outlook
NWS Alaska Pacific River Forecast Center Anchorage AK
300 PM AKDT FRI MAR 29 2024


...UPDATED BREAKUP OUTLOOK ISSUED 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/ESFAK_ACR_20240329.pdf



...SPRING BREAKUP OUTLOOK FOR ALASKA...

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

Recent river ice observations confirm jumbled ice, suggesting normal
to above normal thicknesses in reaches on the Middle and Upper Yukon
River, as well as in the Kuskokwim River below Aniak.

...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 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. 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 recent reports indicating that river
ice has begun to deteriorate, and/or soften in some locations. No
freeze-up jams or mid-winter breakups were reported across the Yukon
and Kuskokwim River basins.


...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 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 139% to 200% of normal. Near
normal FDD conditions have been observed across Southcentral and
Copper River Valley, averaging approximately 98% of normal. 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.  Since March 1st, there has been a 10-25% increase in
snowpack for Eastern AK along the ALCAN Border.

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 snowpack in the Copper Basin is notably
above normal, ranging between 120-140% of the March 1st average. 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 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.

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 outlook favors above normal
temperatures through April for all of Alaska.  Across interior
locations from the Alcan Border to the West Coast, there`s a 40-50%
chance of above-normal temperatures.  In southwest and southcentral
Alaska, the probability is slightly lower, with a 33-40% chance
still favoring above-normal temperatures. Looking ahead for the next
three months, including April, May, and June, there`s an elevated
probability (40-60% chance) 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 Spring Breakup Outlook will be published April 5, 2024.


$$
JSO/JW