Flood Potential Outlook - Alaska


FGAK78 PACR 172156
ESFAK 
AKZALL-100000-

HYDROLOGIC OUTLOOK 
NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK 
2 PM ADT FRI APRIL 17 2015

...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 AND ICE THICKNESS
REPORTS AND MEDIUM TO LONG RANGE TEMPERATURE AND PRECIPITATION FORECASTS.
CURRENTLY BREAKUP AT MOST LOCATIONS IS EXPECTED TO BE A FEW DAYS EARLIER THAN
NORMAL. ALTHOUGH FLOOD POTENTIAL IS RATED AS LOW... FLOODING CAN STILL OCCUR  
IF ICE JAMS FORM DOWNSTREAM OF A VILLAGE.

TEMPERATURES - TEMPERATURES ACROSS THE STATE OVER THE PAST FEW DAY WERE NEAR
NORMAL. A WARMING TREND IS EXPECTED TO OCCUR THE MIDDLE OF NEXT WEEK WHICH
SHOULD CAUSE TEMPERATURES ACROSS INTERIOR ALASKA TO RISE ABOVE NORMAL AND ARE
FORECAST TO REMAIN ABOVE NORMAL THROUGH THE LAST WEEK OF APRIL. THE LONGER
RANGE TEMPERATURE OUTLOOK FOR MAY IS FOR ABOVE NORMAL TEMPERATURES STATEWIDE.

PRECIPITATION - PRECIPITATION IS NOT EXPECTED TO BE A SIGNIFICANT FACTOR IN
THIS YEAR'S BREAKUP PROCESS. 

FOR MORE INFORMATION ON THE TEMPERATURE AND PRECIPITATION OUTLOOKS PLEASE REFER
TO THE CLIMATE PREDICTION CENTER WEB SITE AT HTTP://WWW.CPC.NCEP.NOAA.GOV/

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 60 AND 133
PERCENT OF NORMAL. MANY LOCATIONS IN THE TANANA BASIN REPORTED BELOW NORMAL
THICKNESS.  ICE THICKNESS IN SOUTHWESTERN... SOUTHCENTRAL... WESTERN... AND
INTERIOR ALASKA ARE BELOW NORMAL. ICE THICKNESS LIKELY IS BELOW NORMAL IN 
THE LOWER YUKON... NORMAL IN THE MIDDLE YUKON AND NORMAL TO ABOVE NORMAL IN THE
UPPER YUKON BASIN. ACCUMULATED FREEZING DEGREE DAYS ARE WELL BELOW NORMAL 
OVER MOST OF ALASKA.

SNOW - THE APRIL 1ST SNOWPACK ANALYSIS SHOWS BELOW AVERAGE CONDITIONS IN
WESTERN ALASKA... NORMAL TO ABOVE NORMAL IN NORTHERN ALASKA... BELOW NORMAL
IN SOUTHEAST... NORMAL TO BELOW NORMAL IN INTERIOR ALASKA... AND NORMAL 
TO ABOVE NORMAL IN MOST OF THE CANADIAN YUKON. SNOW MONITORING SITES IN THE 
CANADIAN YUKON ARE REPORTING 70-150 PERCENT OF NORMAL. SOUTHCENTRAL AND
WESTERN ALASKA ARE REPORTING WELL BELOW NORMAL SNOWPACK... WITH LESS THAN
50% OF NORMAL IN THE KUSKOKWIM BASIN AND THE LOWER YUKON.  

FOR WEATHER... ICE AND SNOW CONDITIONS... PLEASE REFER TO
HTTP://WWW.APRFC.ARH.NOAA.GOV/FCST.PHP?PRODUCT=AGAK78PACR AND FOR VARIOUS SNOW
GRAPH OPTIONS... REFER TO THE APRFC WEB SITE AT HTTP://APRFC.ARH.NOAA.GOV OR
THE NRCS WEB SITE AT HTTP://WWW.AK.NRCS.USDA.GOV/SNOW/DATA/CURRENT.HTML 

BREAKUP: NORMALLY SPRING BREAKUP IS DYNAMIC AND MOVES FROM THE HEADWATERS OF A
RIVER DOWNSTREAM IN A LINEAR FASHION. THE COMBINATION OF LOW SNOWFALL IN
WESTERN ALASKA COMBINED WITH THE POSSIBILITY OF ABOVE NORMAL STATEWIDE
TEMPERATURES OVER THE NEXT 4-6 WEEKS WILL LIKELY RESULT IN A THERMAL BREAKUP
FOR RIVERS IN SOUTHCENTRAL AND SOUTHWEST ALASKA. A THERMAL BREAKUP OCCURS WHEN
THERE IS NOT ENOUGH SNOWMELT TO PUSH ICE DOWNSTREAM AND TEMPERATURES GENERALLY 
WARM UP SLOWLY. IN A THERMAL BREAKUP... EVEN THOUGH ICE STRENGTH DETERIORATES 
SIGNIFICANTLY... BREAKUP CAN OCCUR LATER THAN NORMAL. ALSO... NO COHERENT 
BREAKUP FRONT DEVELOPS IN THIS SCENARIO... AND MULTIPLE LOCATIONS MAY BEGIN  TO
SEE ICE MOVEMENT SIMULTANEOUSLY. ICE JAM FLOODING FROM A THERMAL BREAKUP IS
RARELY SERIOUS... BUT STILL POSSIBLE. TIMING OF BREAKUP DURING A THERMAL
BREAKUP MIGHT RANGE FROM SEVERAL DAYS EARLIER TO SEVERAL DAYS LATER THAN 
NORMAL... AND IS OFTEN INCONSISTENT UP AND DOWN THE RIVER.   

THE OUTLOOK FOR SIGNIFICANT PRECIPITATION IS LOW AND UNLIKELY TO INFLUENCE
BREAKUP THIS YEAR. EVEN WITH THIN ICE AND LOW SNOWPACK... A FASTER THAN
EXPECTED RISE IN TEMPERATURES OR A SIGNIFICANT RAIN EVENT COULD PRODUCE RAPID
MELT AND HIGHER THAN EXPECTED FLOWS... RESULTING IN ICE JAMS FORMING
AND INCREASED RISK OF FLOODING.

BREAKUP IS EXPECTED TO BE THERMAL IN SOUTHERN... SOUTHWESTERN... WESTERN ... 
AND INTERIOR AREAS OF THE STATE... WITH THERMAL TO DYNAMIC BREAKUP IN
NORTHEASTERN AREAS... SPECIFICALLY IN THE UPPER YUKON AREA... AND DYNAMIC 
ON THE NORTH SLOPE. FLOOD POTENTIAL FROM ICE JAMS WILL BE LOW FOR MOST OF 
THE STATE... WITH THE UPPER YUKON BEING THE PRIMARY AREA WITH A NORMAL 
FLOOD POTENTIAL FOR THE STRETCH FROM EAGLE DOWNSTREAM TO FORT YUKON. 

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THE FOLLOWING TABLE GIVES ESTIMATES FOR FLOOD POTENTIAL... BASIN RUNOFF
VOLUMES... AVERAGE BREAKUP DATES (1970-2015)... AND AN INITIAL RANGE FOR SPRING

BREAKUP ESTIMATES FOR VARIOUS LOCATIONS AND BASINS THROUGHOUT THE STATE. 

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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.

*  AVERAGE BREAKUP DATES ARE FOR THE PERIOD 1970 THROUGH 2015 AND ARE
      CALCULATED FOR LOCATIONS WITH AT LEAST 5 YEARS OF DATA.
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                      SNOWMELT   FLOOD      AVERAGE  NO. OF  FORECAST
RIVER - REACH         RUNOFF     POTENTIAL  BREAKUP  YEARS   BREAKUP
                      VOLUME                DATE *   RECORD  DATE
-------------         ---------- ---------  -------  ------  --------
SOUTHEAST PANHANDLE    BELOW

KENAI RIVER            BELOW

ANCHOR RIVER           BELOW                 04/14     10       

MATANUSKA RIVER        BELOW                 04/30      7   04/18-04/24

SUSITNA RIVER          BELOW
GOLD CREEK                          LOW      05/03      6   04/27-05/03
SUNSHINE                            LOW      05/03     21   04/27-05/03

YENTNA RIVER           BELOW
LAKE CREEK                          LOW      05/02     21   04/26-05/02

SKWENTNA RIVER         BELOW
SKWENTNA                            LOW      05/01     17   04/25-05/02

COPPER RIVER BASIN    AVERAGE
GAKONA RVR @ HWY                    LOW      05/02     25
GULKANA RVR @ HWY                   LOW      05/01     24

CHENA RIVER           AVERAGE
CHENA LAKES PROJECT                 LOW
FAIRBANKS                           LOW      04/26     25   04/21-04/26

TANANA RIVER          AVERAGE
NORTHWAY                            LOW      04/26     26   04/20-04/26
SALCHA                              LOW
FAIRBANKS                           LOW      04/30     13   04/24-04/30
NENANA                              LOW      05/01     38   04/25-05/01
MANLEY                              LOW      05/04     20   04/29-05/05

KUSKOKWIM RIVER        BELOW
NIKOLAI                             LOW      04/24     27     04/15**
MCGRATH                             LOW      05/07     38   04/26-05/03
STONY RIVER                         LOW      05/06     24   04/28-05/04
SLEETMUTE                           LOW      05/06     23   04/28-05/05
RED DEVIL                           LOW      05/07     26   04/30-05/06
CROOKED CREEK                       LOW      05/07     26   04/30-05/06
ANIAK                               LOW      05/08     29   04/30-05/06
KALSKAG                             LOW      05/08     23   04/30-05/06
TULUKSAK                            LOW      05/10     20   05/02-05/08
AKIAK                               LOW      05/11     26   05/03-05/09
KWETHLUK                            LOW
BETHEL                              LOW      05/12     41   05/03-05/09
NAPAKIAK                            LOW      05/14     18   05/05-05/11

YUKON RIVER (UPPER)   AVERAGE
DAWSON, YT                          LOW      05/05     41   04/30-05/06
EAGLE                               LOW      05/05     32   04/30-05/06
CIRCLE                            LOW-MOD    05/10     30   05/03-05/09
FORT YUKON                          LOW      05/11     29   05/04-05/10
BEAVER                              LOW      05/11     17   05/04-05/10
STEVENS VILLAGE                     LOW      05/12     17   05/05-05/11
RAMPART                             LOW      05/12     17   05/05-05/11

YUKON RIVER (MIDDLE)   BELOW
TANANA                              LOW      05/10     27   05/01-05/07
RUBY                                LOW      05/12     28   05/03-05/09
GALENA                              LOW      05/13     29   05/04-05/10
KOYUKUK                             LOW      05/13          05/05-05/11
NULATO                              LOW      05/13     16   05/05-05/11
KALTAG                              LOW      05/14     36   05/06-05/12
ANVIK                               LOW      05/17     25   05/07-05/13

YUKON RIVER (LOWER)    BELOW
HOLY CROSS                          LOW      05/16     25   05/05-05/11
RUSSIAN MISSION                     LOW      05/16     27   05/05-05/11
MARSHALL                            LOW      05/16     21   05/05-05/11
PILOT STATION                       LOW      05/17     15   05/06-05/12
MOUNTAIN VILLAGE                    LOW      05/19     25   05/08-05/14
ALAKANUK/EMMONAK                    LOW      05/23     27   05/12-05/18

KOYUKUK RIVER         AVERAGE
BETTLES                             LOW      05/10     30   05/01-05/07
ALLAKAKET                           LOW      05/11     25   05/02-05/08
HUGHES                              LOW      05/11     24   05/03-05/09

SEWARD PENINSULA       BELOW

BUCKLAND RIVER         BELOW
BUCKLAND                          LOW-MOD    05/18     21   05/13-5/19

KOBUK RIVER            BELOW
KOBUK                             LOW-MOD    05/17     32   05/05-05/11
SHUNGNAK                            LOW      05/18     22   05/06-05/12
AMBLER                              LOW      05/19     29   05/07-05/13

NOATAK RIVER          AVERAGE
NOATAK                              LOW      05/20     17   05/17-05/23

BROOKS RANGE - NORTH  AVERAGE
COLVILLE @ UMIAT                    LOW      05/24     12   05/21-05/27
COLVILLE @ COLVILLE                 LOW      06/02     15   05/30-06/05
SAGAVANIRKTOK NR PRUDHOE            HIGH*    05/25     19   05/21-05/29

*NWS HAS NO RECORD OF ICE JAM RELATED FLOODS FOR THE SAGVANIRKTOK. CONSIDERING
CURRENT AUFEIS FLOODING CONDITIONS A HIGH FLOOD POTENTIAL EXISTS FOR MORE
FLOODING DURING THE SNOWMELT AND RIVER ICE BREAKUP PROCESS. 

FOR MORE DETAIL AND TO SEE A FLOOD POTENTIAL MAP REFER TO OUR WEB
SITE AT HTTP://APRFC.ARH.NOAA.GOV.

THE NEXT SPRING BREAKUP OUTLOOK IS SCHEDULED AT 2 PM FRIDAY APRIL 24
2015.

$$
DPS