Flood Potential Outlook
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FGAK78 PACR 252147
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AKZALL-140000-

HYDROLOGIC OUTLOOK
NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK
2 PM ADT TUE APRIL 25 2017

...Spring 2017 Breakup Outlook for Alaska....

Several locations are reported as open. Short range temperature and
precipitation forecasts have changed since Monday`s outlook. No changes have
been made to the Breakup Forecast. Observers are reporting some open water along
the Susitna, Tanana, Nenana, Copper, Susitna, and Kuskokwim rivers. Reports
suggest caution should be exercised while traveling on the Kuskokwim River near
Bethel and below and above Akiak. Open leads have been seen along the Yukon
River near Eagle, AK. Many small streams around the Buckland area are reported
as having dark ice. See below for details.

The flood potential from snowmelt and ice jams throughout most of Alaska this
spring is currently rated as normal. This would indicate that locations that
often experience flooding during breakup are likely to see minor flooding if an
ice jam forms downstream. The central Tanana Valley has a slightly higher risk
of minor flooding this spring due to a greater than normal winter snowpack.

Breakup along the Middle and Lower Yukon River and Tanana River is expected to
be 1 to 3 days earlier than average, while breakup along the Kuskokwim and other
Southeast and Southern Alaskan rivers is expected to be 2 to 4 days earlier than
average. This statewide forecast is based on current ice thickness, observed
snowpack, river freeze-up stage, and short and long range weather forecasts.

Temperatures

Temperatures over the next few weeks are expected to be near normal in
eastern interior parts of Alaska and into Canada. The rest of the state likely
to have above normal temperatures. The outlook for the month of May suggests
North Slope temperatures are expected to be near normal with above normal
temperatures south of the Brooks Range into southern parts of the state.

Precipitation

Over the next week, precipitation is expected to be below normal along the
central to western Brooks Range and into the Seward Peninsula. Expect above
normal precipitation south of the Alaska Range and into southwestern and
southeastern Alaska. Remaining locations in the state are expected to have near
normal precipitation. The outlook for the following week suggests above normal
precipitation south of the Alaska Range and into southwestern and southeastern
Alaska with the remaining locations at near normal precipitation. The May
outlook suggests below normal precipitation along the western coast to just
north of the Seward Peninsula. Normal amounts of precipitation are expected in
all other locations of the state.

For more information on the outlooks, please refer to the Climate Prediction
Center website http://www.cpc.ncep.noaa.gov/

Ice conditions



April ice thickness data are available for a limited number of observing sites
in Alaska. April 1st measurements indicate that ice thickness is generally
slightly above normal across most of the state.

Snowpack


An analysis of the April 1st snowpack by the Natural Resources Conservation
Service (NRCS) indicates a generally below normal snowpack south of the Alaska
Range, including Southeast Alaska. North of the Alaska Range, there is an area
of well above normal snowpack east of Fairbanks, but overall averages within the
Middle and Upper Yukon basins are close to normal. Snowpack conditions along the
Dalton highway on the North Slope of Alaska are near normal. For more details,
please refer to the various snow graphics from the Alaska-Pacific River Forecast
Center (APRFC) or from the Natural Resources Conservation Service (NRCS).


For weather, ice, and snow conditions, please refer to
http://www.weather.gov/aprfc/FGAK78PACR and for various snow graph options refer
to the APRFC website at http://www.weather.gov/aprfc or the NRCS website at
http://www.nrcs.usda.gov/wps/portal/nrcs/main/ak/snow/

Breakup

The breakup of river ice generally falls between dynamic and thermal processes.
A thermal breakup commonly occurs when snowmelt and other runoff water is
insufficient to influence ice movement and the ice rots in place. During a
thermal breakup, ice strength significantly deteriorates, but the movement of
ice and snowmelt downstream does not form a coherent breakup front. In this case
multiple locations might see simultaneous ice movement. Flooding from ice jams
during a thermal breakup is rarely serious, although still possible. During a
thermal process, breakup timing at locations might range from several days
earlier to several days later than expected and is often inconsistent up and
down the river. Normally, spring breakup is dynamic, progressing from river
headwaters to downstream locations. Dynamic breakups are characterized by having
higher flows, more potential for ice jams, and flooding from these events can be
catastrophic. Typically a dynamic breakup progresses from upstream to
downstream. Most dynamic breakups occur when air temperatures shift from being
cooler than normal to warmer than normal.

From the expected statewide temperature outlooks, the 2017 breakup season is
expected to be earlier than average south of the Brooks Range. Breakup along the
North Slope, and Porcupine and Canadian Yukon rivers is expected to be on
average. Breakup along the Middle and Lower Yukon River and Tanana River is
expected to be 1 to 3 days earlier than average, while breakup along the
Kuskokwim and other southeast and southern Alaska rivers is expected to be 2 to
4 days earlier than average.

Observed River Conditions

Susitna: Talkeetna has open water near the Railroad bridge. The Chulitna
and Susitna rivers have some open water. Deshka River has open leads forming.
Skwentna River at Skwentna is open with ice floes from upstream.

Tanana: The Tanana River has some open water upstream of Chena River to the
Salcha River.The Tanana River between Big Delta and Tanacross is mostly open.
Some open water has been reported along the mid section of Nenana River. The
lower portion of Chena River is mostly open water and the mid portion has some
open water. The lower portion of Salcha River has some open water.

Copper River: Some open water has been reported along the Copper River between
Christochina south to Copper Center. Gakona and Gulkana rivers have open leads.

Kuskokwim: Nikolai is open. Some open water has been observed upstream of
Nikolai near Old Nikolai. Observations at Sleetmute show open water at the
shore. Reports suggest caution should be exercised while traveling on the
river near Bethel and below and above Akiak.

Yukon: Pilots have reported a few open leads along the Yukon River shore near
Eagle, AK and the Canadian/U.S border.

--------------------------------------------------------------------------------
The following table gives (1) an estimate of flood potential for various
locations around the state and (2) basin runoff volumes.
--------------------------------------------------------------------------------
Snowmelt runoff volume: expected water volume from snowmelt during the melt
season.

Flood Potential: the likelihood of flooding from snowmelt and/or ice jams. This
is initially calculated based on the flood frequency for the 2000 to 2016
historical record and adjusted to reflect current conditions.

*  Average breakup dates are for the 1980-2016 period and are calculated for
locations with at least 5 years of data.

** Actual breakup date for this year.
--------------------------------------------------------------------------------

                      Snowmelt   Flood      Average  NO. of  Forecast
River - Reach         Runoff     Potential  Breakup  Years   Breakup
                      Volume                Date *    Used    Date
-------------         ---------- ---------  -------  ------  --------
Southeast Panhandle

Kenai River                                                   Open

Anchor River        Below Average  Low       04/14     11     4/13**

Matanuska River     Below Average            04/30      8     Open

Susitna River       Below Average
  Gold Creek                       Low       05/03      8  04/27-05/03
  Sunshine                         Low       05/03     27  04/27-05/03

Yentna River        Below Average
  Lake Creek                       Low       05/01     25  04/28-05/01

Skwentna River      Below Average
  Skwentna                         Low       04/30     21     4/24**

Copper River Basin  Below Average
  Gakona Rvr @ HWY                 Low       05/01     29  04/25-05/01
  Gulkana Rvr @ HWY                Low       04/29     28  04/23-04/29

Chena River         Above Average
  Chena Lakes Project
  Fairbanks                      Low-Mod     04/26     24  04/22-04/28

Tanana River        Above Average
  Chisana @ Northway               Low       04/26     27     4/25**
  Salcha                         Low-Mod
  Fairbanks                        Low       04/29     18  04/24-04/30
  Nenana                           Low       04/30     37  04/25-05/01
  Manley                           Low       05/04     27  04/30-05/06

Kuskokwim River     Below Average
  Nikolai                          Low       04/23     31     4/23**
  McGrath                        Low-Mod     05/05     37  04/30-05/06
  Stony River                      Low       05/02     29  04/30-05/06
  Sleetmute                      Low-Mod     05/02     28  04/28-05/04
  Red Devil                      Low-Mod     05/05     31  04/29-05/05
  Crooked Creek                  Low-Mod     05/06     31  04/30-05/06
  Aniak                          Low-Mod     05/07     34  05/01-05/07
  Kalskag                          Low       05/07     28  05/01-05/07
  Tuluksak                         Low       05/08     25  05/03-05/09
  Akiak                            Low       05/10     31  05/03-05/09
  Kwethluk                       Low-Mod     05/10      6  05/03-05/09
  Bethel                           Low       05/11     37  05/04-05/10
  Napakiak                         Low       05/12     22  05/05-05/11

Yukon River (Upper)   Average
  Dawson, YT                                 05/04     36  04/30-05/06
  Eagle                         Low-Mod      05/04     36  04/30-05/06
  Circle                          Mod        05/08     33  05/04-05/10
  Fort Yukon                    Low-Mod      05/10     33  05/05-05/11
  Beaver                          Low        05/10     21  05/06-05/12
  Stevens Village               Low-Mod      05/11     20  05/07-05/13
  Rampart                         Low        05/11     22  05/07-05/13

Yukon River (Middle)  Average
  Tanana                          Low        05/08     32  05/05-05/11
  Ruby                            Low        05/09     31  05/06-05/12
  Galena                        Low-Mod      05/11     36  05/07-05/13
  Koyukuk                       Low-Mod      05/09     12  05/07-05/13
  Nulato                        Low-Mod      05/10     21  05/07-05/13
  Kaltag                          Low        05/12     31  05/09-05/15
  Anvik                           Low        05/14     30  05/11-05/17

Yukon River (Lower)   Average
  Holy Cross                      Low        05/15     30  05/10-05/16
  Russian Mission                 Low        05/16     31  05/09-05/15
  Marshall                      Low-Mod      05/15     25  05/10-05/16
  Pilot Station                   Low        05/16     20  05/11-05/17
  Mountain Village                Low        05/19     30  05/12-05/18
  Alakanuk/Emmonak                Mod        05/21     32  05/17-05-23

Koyukuk River         Average
  Bettles                         Low        05/10     35  05/07-05/13
  Allakaket                       Low        05/10     31  05/07-05/13
  Hughes                        Low-Mod      05/11     30  05/07-05/14

Seward Peninsula      Average
  Buckland                        Mod        05/20     26  05/17-05/23

Kobuk River           Average
  Kobuk                         Low-Mod      05/14     33  05/11-05/17
  Shungnak                        Low        05/17     27  05/14-05/20
  Ambler                          Low        05/18     33  05/15-05/21

Noatak River          Average
  Noatak                          Low        05/19     22  05/16-05/22

Brooks Range - North  Average
  Colville @ Umiat                Low        05/25     17  05/22-05/28
  Colville @ Colville           Low-Mod      06/04     19  06/01-06/07

Sagavanirktok River   Average
  Dalton HWY                    Low-Mod      **/**


For more detail and to see a flood potential map refer to our website at
http://www.weather.gov/aprfc/

The next spring breakup outlook is scheduled at 2 PM ADT Thursday April 27 2017

$$
ehm



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