National Weather Service United States Department of Commerce

758
FGAK78 PACR 172000
ESFAK
AKZALL-140000-

HYDROLOGIC OUTLOOK
NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK
1 PM ADT APRIL 17 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 MOST LOCATIONS IS EXPECTED TO BE AT AVERAGE OR A FEW DAYS
LATER THAT NORMAL. SEE TABLE AT BOTTOM OF PRODUCT FOR SPECIFIC LOCATIONS.

TEMPERATURES - DAILY TEMPERATURES OVER THE NEXT FEW WEEKS ON AVERAGE ARE
LIKELY TO BE ABOVE NORMAL OVER THE WESTERN INTERIOR... SOUTHCENTRAL AND SOUTH
WESTERN PORTION OF THE STATE WITH TEMPERATURES NEAR NORMAL IN THE UPPER YUKON
AND PORCUPINE RIVER BASINS. OVER THE NEXT SEVEN DAILY TEMPERATURES WILL COOL OFF
FROM BEING ABOVE NORMAL TO NEAR NORMAL AS A COLDER LOW PRESSURE SYSTEM IS
FORECAST TO MOVE SOUTH ACROSS INTERIOR ALASKA.

PRECIPITATION - PRECIPITATION IS NOT EXPECTED TO BE A SIGNIFICANT FACTOR IN THIS
YEARS BREAKUP PROCESS. PRECIPITATION OVER THE MAINLAND IS LIKELY TO BE NEAR OR
BELOW NORMAL FOR APRIL. THE OUTLOOK SUGGESTS ABOVE NORMAL PRECIPITATION IN
INTERIOR AND NORTHERN 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 PENNINSULA... 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 BROOK RANGE TO THE SEWARD
PENNISULA 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.

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
---------------------------------------------------------------------
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
---------------------------------------------------------------------

                      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  04/25-04/01
  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  04/19-04/25
  MCGRATH                       LOW-MOD      05/04     38  05/02-05/08
  STONY RIVER                     LOW        05/02     30  04/28-05/04
  SLEETMUTE                     LOW-MOD      05/02     29  04/28-05/04
  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  05/03-05/09
  KALSKAG                         LOW        05/07     29  05/04-05/10
  TULUKSAK                        LOW        05/07     26  05/04-05/10
  AKIAK                           LOW        05/09     32  05/05-05/11
  KWETHLUK                      LOW-MOD      05/10      6  05/07-05/13
  BETHEL                          LOW        05/10     38  05/07-05/13
  NAPAKIAK                        LOW        05/11     23  05/07-05/13

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  05/04-05/10
  FORT YUKON                      LOW        05/10     34  05/05-05/11
  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  05/05-05/11
  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  05/09-05/15
  NULATO                        LOW-MOD      05/10     22  05/09-05/15
  KALTAG                          LOW        05/12     32  05/10-05/16
  ANVIK                           LOW        05/14     31  05/10-05/16

YUKON RIVER (LOWER)  ABOVE AVERAGE
  HOLY CROSS                      LOW        05/15     31  05/12-05/18
  RUSSIAN MISSION                 LOW        05/16     32  05/08-05/14
  MARSHALL                      LOW-MOD      05/15     26  05/12-05/18
  PILOT STATION                   LOW        05/15     21  05/13-05/19
  MOUNTAIN VILLAGE                LOW        05/19     31  05/13-05/19
  ALAKANUK/EMMONAK              LOW-MOD      05/21     32  05/19-05-25

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 APRIL 24 2018

$$
DPS