Flood Potential Outlook
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FGAK78 PACR 242059
ESFAK
AKZALL-140000-

HYDROLOGIC OUTLOOK
NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK
1 PM ADT APRIL 24 2018

...SPRING BREAKUP OUTLOOK FOR ALASKA....

The spring breakup flood potential is currently rated as low to low-moderate
statewide. This forecast is based on observed snowpack, ice thickness reports,
and medium to long range temperature and precipitation forecasts. Currently,
breakup at many interior and north slope locations is expected to be at the
normal time or a few days later than normal. Temperatures in the lower Yukon
river downstream from russian mission and along the lower Kuskokwim river
downstream from Red Devil have been warmer than anticipated. Breakup along these
portions of the rivers is expected to be three to six days earlier than median
breakup dates. See table at bottom of product for specific locations.

Temperatures - daily temperatures over the next few days will continue being
normal to below normal as a colder low pressure system is moving southward
across Southern and Interior Alaska. The rest of the state is still forecasted
to be above normal. Beyond the upcoming week, the next few weeks are likely to
be above normal over the entire state, except in the eastern Interior where it`s
likely temps will be near normal.

Precipitation - precipitation is not expected to be a significant factor in this
year`s breakup process. Precipitation over the mainland is likely to be near or
above normal for the remainder of april and continuing to be below normal in
Southeast. The outlook suggests above normal precipitation in interior and
western Alaska for the April-May-June period.

Ice - April ice thickness data are available for a limited number of observing
sites in alaska. April 1st measurements indicate that ice thickness is variable
across the state, with locations generally between 50 and 110 percent of normal.
Locations in the Tanana basin reported below normal thickness. Ice thickness in
western Alaska are below normal. Ice thickness in the lower Yukon likely is
below normal. Normal to below normal ice thickness is indicated in the middle
and upper Yukon Basin.

Snow - the April 1 snowpack analysis indicates below average to average
conditions north of the brooks range and in the upper yukon region. Above
average snowpack south of the brooks range to the Seward Peninsula, and in the
Interior, Middle Yukon, and Tanana Basin. Below average snowpack in southwestern
Alaska, along Cook Inlet, and the Panhandle portions of Alaska.


Further information can be found at the following web sites:
Weather... https://www.weather.gov/aprfc/forecasts/agak78pacr
Snow... Https://www.weather.gov/aprfc/nrcs_ak_swe and
https://www.weather.gov/aprfc/snow_depth or from the nrcs...
https://www.wcc.nrcs.usda.gov/snow/ ice thickness...
https://www.weather.gov/aprfc/icethickness climate prediction...
http://www.cpc.ncep.noaa.gov/


Breakup:
A dynamic breakup moves from the headwaters of a river downstream in a somewhat
linear fashion and often during the process ice jams occur that can cause
flooding. Average to above average snowpack volumes in the middle Yukon, Tanana
Basin, Fairbanks, and south of the Brooks Range to the Seward Peninsula regions
combined with possible above average temperatures might result in a dynamic
breakup scenario. A thermal breakup is where the river ice rots in place
primarily due to a gradual warm up and little snowmelt runoff. A thermal breakup
usually results in fewer ice jams and less chance of flooding. A thermal breakup
on the lower Kuskokwim and Yukon Rivers is more likely due to forecasted warmer
than normal temperatures in april and thin river ice.

The outlook for significant precipitation is low and unlikely to be influential
to breakup this year. In regions with thin ice and low snowpack. A faster than
expected rise in temperatures combined with high snowpack volume could produce
rapid melt and higher than expected flows producing high water conditions, and
possible bankfull river stage conditions. These conditions can result in
significant ice jams and increased risk of flooding.

Observed river conditions

Kuskokwim: ice has moved out of Nikolai. Ice conditions on the
lower river are unsafe for travel below Tuluksak.

The following table gives an estimation of flood potential for
various locations around the state and basin runoff volumes.

For more detail and to see a flood potential map refer to our web
site at https://www.weather.gov/aprfc/floodpotential


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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 2017 historical record and adjusted to reflect
current conditions.

* average (median) breakup dates are for the period 1980 through
2017 and are calculated for locations with at least 5 years of data.
** actual breakup date for this year


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                      SNOWMELT    FLOOD     AVERAGE  NO. OF  FORECAST
RIVER - REACH          RUNOFF    POTENTIAL  BREAKUP  YEARS   BREAKUP
                       VOLUME                DATE*    USED    DATE
-------------         ---------- ---------  -------  ------  --------
SOUTHEAST PANHANDLE      BELOW

KENAI RIVER              BELOW    LOW

ANCHOR RIVER             BELOW    LOW

MATANUSKA RIVER         AVERAGE   LOW

SUSITNA RIVER           AVERAGE
  GOLD CREEK                      LOW
  SUNSHINE                        LOW        05/03     29  04/30-05/06

YENTNA RIVER             BELOW
  LAKE CREEK                      LOW        05/01     27  04/29-05/04

SKWENTNA RIVER           BELOW
  SKWENTNA                        LOW        04/30     23  04/27-05/03

COPPER RIVER BASIN   ABOVE AVERAGE
  GAKONA RVR @ HWY                LOW        04/30     30  04/27-05/03
  GULKANA RVR @ HWY               LOW        04/30     29  05/27-04/03

CHENA RIVER          ABOVE AVERAGE
  CHENA LAKES PROJECT
  FAIRBANKS                       LOW        04/26     26  04/24-04/30

TANANA RIVER         ABOVE AVERAGE
  CHISANA @ NORTHWAY              LOW        04/26     27  04/18-04/24
  SALCHA                          LOW
  FAIRBANKS                       LOW        04/29     19  04/25-05/01
  NENANA                          LOW        04/30     38  04/26-05/02
  MANLEY                          LOW        05/03     27  04/30-05/06

KUSKOKWIM RIVER        AVERAGE
  NIKOLAI                         LOW        04/23     32    **4/24
  MCGRATH                       LOW-MOD      05/04     38  05/02-05/08
  STONY RIVER                     LOW        05/02     30  04/29-05/05
  SLEETMUTE                     LOW-MOD      05/02     29  04/30-05/06
  RED DEVIL                     LOW-MOD      05/04     32  04/29-05/05
  CROOKED CREEK                 LOW-MOD      05/05     32  05/01-05/07
  ANIAK                         LOW-MOD      05/07     35  05/01-05/07
  KALSKAG                         LOW        05/07     29  04/30-05/06
  TULUKSAK                        LOW        05/07     26  05/02-05/08
  AKIAK                           LOW        05/09     32  05/02-05/08
  KWETHLUK                      LOW-MOD      05/10      6  05/02-05/08
  BETHEL                          LOW        05/10     38  05/02-05/08
  NAPAKIAK                        LOW        05/11     23  05/04-05/10

YUKON RIVER (UPPER)    AVERAGE
  DAWSON, YT                      LOW        05/04     38  05/04-05/10
  EAGLE                           LOW        05/04     37  05/03-05/09
  CIRCLE                        LOW-MOD      05/08     34  05/07-05/13
  FORT YUKON                      LOW        05/10     34  05/07-05/13
  BEAVER                          LOW        05/10     22  05/08-05/14
  STEVENS VILLAGE                 LOW        05/11     21  05/09-05/15
  RAMPART                         LOW        05/11     23  05/09-05/15

YUKON RIVER (MIDDLE) ABOVE AVERAGE
  TANANA                          LOW        05/08     33  05/07-05/13
  RUBY                            LOW        05/09     32  05/07-05/13
  GALENA                        LOW-MOD      05/11     37  05/08-05/14
  KOYUKUK                       LOW-MOD      05/10     13  05/08-05/14
  NULATO                        LOW-MOD      05/10     22  05/09-05/15
  KALTAG                          LOW        05/12     32  05/09-05/15
  ANVIK                           LOW        05/14     31  05/12-05/18

YUKON RIVER (LOWER)  ABOVE AVERAGE
  HOLY CROSS                      LOW        05/15     31  05/12-05/18
  RUSSIAN MISSION                 LOW        05/16     32  05/11-05/17
  MARSHALL                      LOW-MOD      05/15     26  05/11-05/17
  PILOT STATION                   LOW        05/15     21  05/12-05/18
  MOUNTAIN VILLAGE                LOW        05/19     31  05/13-05/19
  ALAKANUK/EMMONAK              LOW-MOD      05/21     32  05/16-05-22

KOYUKUK RIVER       ABOVE AVERAGE
  BETTLES                         LOW        05/09     36  05/08-05/14
  ALLAKAKET                       LOW        05/09     32  05/08-05/14
  HUGHES                        LOW-MOD      05/11     31  05/09-05/15

SEWARD PENINSULA    ABOVE AVERAGE
  BUCKLAND                      LOW-MOD      05/20     28  05/18-05/24

KOBUK RIVER         ABOVE AVERAGE
  KOBUK                         LOW-MOD      05/14     34  05/12-05/18
  SHUNGNAK                        LOW        05/17     28  05/15-05/21
  AMBLER                          LOW        05/17     34  05/18-05/21

NOATAK RIVER        ABOVE AVERAGE
  NOATAK                          LOW        05/19     22  05/17-05/23

BROOKS RANGE - NORTH  AVERAGE
  COLVILLE @ UMIAT                LOW        05/25     18  05/25-05/31
  COLVILLE @ COLVILLE             LOW        06/03     20  06/04-06/10

SAGAVANIRKTOK RIVER   AVERAGE
  DALTON HWY                      LOW

The next Spring Breakup Outlook is scheduled at 2 pm ADT Tueday May 1 2018



$$
JEC&EHM



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