Flood Potential Outlook
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
FGAK78 PACR 151849

11AM ADT THU MAR 15 2018


The Spring Breakup flood potential in the Tanana River Valley is currently
rated as above average. The Central Yukon River, Koyukuk River, Copper River,
and North Slope are rated as slightly above average flood potential. In the
rest of the state, flood potential is rated as average or below average. This
forecast is based on observed snowpack, ice thickness reports, and long-range
temperature forecasts.

Ice conditions

March ice thickness data are available for a limited number of observing sites
in Alaska. Late February/Early March measurements indicate that ice thickness
is variable across the state with locations generally between 75-100 percent
of normal. Many locations in the Tanana Basin are slightly below normal,
with the exception of the Chena River showing only 65 percent of normal ice
thickness. The Yukon River at Eagle has ice slightly thicker than normal, and
the Colville River, up on the Arctic Coastal Plain, has ice slightly thinner
than normal. Accumulated Freezing Degree Days are much lower than normal on
the Arctic Coast, West Coast, and Western Interior indicative of a warmer
than normal winter. Bethel stands out in particular as having only 46% of the
normal Freezing Degree days. Freezing Degree Days in southcentral were close
to normal and the central and eastern Interior Alaska was just below normal.


Analysis of the March 1st snowpack by the Natural Resources Conservation
Service (NRCS) indicates much higher than normal snowpack in the Tanana Basin
(175-200%) and higher than normal in the Central Yukon and Koyukon basins
(150%). The Copper River basin is slightly higher than normal (125%). Other
basins have near normal snowpacks or below, or too few observations exist
to determine basin-wide conditions.

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 average temperatures for most of
April followed by an abrupt transition to warm summer-like temperatures in
late April to early May.  The temperature outlook for late March and early
April suggest an increased chance of below normal temperatures for most
of Alaska.  The longer 3-month outlook which includes March, April and May
indicates increased chances of above average temperatures in Northern and
Western Alaska, trending towards equal chances of above, near, or below normal
temperatures in areas south and east of the Alaska Range. For more information
on the climate forecasts please refer to the Climate Prediction Center.

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.