FGAK78 PACR 292052 ESFAK AKZALL-302000- ALASKA SPRING BREAKUP OUTLOOK NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK 200 PM ADT FRI APR 29 2011 ...SPRING BREAKUP OUTLOOK FOR ALASKA... THE FLOOD POTENTIAL FROM SNOWMELT AND ICE JAMS THIS SPRING BREAKUP SEASON THROUGHOUT ALASKA IS CURRENTLY RATED AS AVERAGE FOR MUCH OF THE STATE WITH SEVERAL AREAS HAVING AN ABOVE AVERAGE THREAT OF FLOODING. BREAKUP DATES ARE EXPECTED TO BE SEVERAL DAYS LATER THAN AVERAGE. THIS FORECAST IS BASED ON OBSERVED SNOWPACK... ICE THICKNESS REPORTS AND LONG RANGE TEMPERATURE FORECASTS. ICE - APRIL ICE THICKNESS DATA ARE AVAILABLE FOR A LIMITED NUMBER OF OBSERVING SITES IN ALASKA. MEASUREMENTS INDICATE THAT ICE THICKNESS AND ACCUMULATED FREEZING DEGREE DAYS ARE NEAR NORMAL ON THE YUKON AND KUSKOKWIM RIVERS. ICE THICKNESS IN SOUTHCENTRAL ALASKA AND SOME SITES IN THE TANANA VALLEY ARE THINNER THAN NORMAL. THE GAKONA RIVER IN THE COPPER RIVER BASIN HAS ACCUMULATED A SIGNIFICANT AMOUNT OF AUFEIS NEAR THE HIGHWAY AT GAKONA JUNCTION AND IS AT A GREATER RISK OF FLOODING THAN NORMAL. ALSO...AN ABNORMAL FALL BREAKUP EVENT ON THE KUSKOKWIM RIVER IN NOVEMBER LEFT STRETCHES OF JUMBLED BREAKUP ICE THAT REFROZE... WHICH MAY AFFECT THE BREAKUP PROCESS AND CAUSE ADDITIONAL ICE JAMS DURING THE SPRING BREAKUP. A SIMILAR SITUATION WITH A FREEZEUP ICE JAM OCCURRED ON THE TANANA RIVER JUST DOWNSTREAM OF MANLEY HOT SPRINGS...LEADING TO JUMBLED ICE THAT REFROZE WITH HIGHER WATER LEVELS THAN USUAL FOR EARLY WINTER. SNOW - AN ANALYSIS OF THE APRIL 1 SNOWPACK BY THE NATURAL RESOURCES CONSERVATION SERVICE (NRCS) INDICATES A BELOW NORMAL SNOWPACK THROUGHOUT SOUTHCENTRAL AND SOUTHWEST ALASKA. THERE IS A NEAR NORMAL SNOWPACK ON THE NORTH SLOPE AND EASTERN BROOKS RANGE AS WELL AS THE YUKON RIVER UPSTREAM OF TANANA. THE SNOWPACK IN WESTERN ALASKA IS WELL ABOVE (BETWEEN 110% AND 150%) OF NORMAL. THERE IS ENOUGH SNOW IN MOST AREAS OF THE STATE TO PRODUCE SIGNIFICANT SNOWMELT RUNOFF PEAKS AND POTENTIAL FLOODING IF SUBJECTED TO A RAPID WARMING PATTERN. FOR MORE DETAILS ON THE SNOWPACK.. PLEASE REFER TO THE VARIOUS SNOW GRAPH OPTIONS AT THE APRFC WEB SITE AT HTTP://APRFC.ARH.NOAA.GOV OR ON THE NRCS WEB SITE AT HTTP://WWW.AK.NRCS.USDA.GOV/SNOW WEATHER - CURRENT OUTLOOKS FROM THE CLIMATE PREDICTION CENTER FOR THE NEXT TWO WEEKS INDICATE A GREATER LIKELIHOOD OF BELOW NORMAL TEMPERATURES AND PRECIPITATION OVER NORTHEAST ALASKA AND A GREATER LIKELIHOOD OF ABOVE NORMAL TEMPERATURES AND PRECIPITATION ALONG THE SOUTHERN COAST OF ALASKA. THE MOST IMPORTANT FACTOR DETERMINING THE SEVERITY OF BREAKUP REMAINS THE WEATHER DURING APRIL AND MAY. THE CURRENT ONE-MONTH OUTLOOK FOR MAY INDICATES EQUAL CHANCES OF NORMAL... BELOW NORMAL AND ABOVE NORMAL TEMPERATURES AND PRECIPITATION. ENSEMBLE WEATHER MODEL RUNS OVER THE NEXT TWO WEEKS SHOW NO PROMINENT FORMATION OF AN UPPER LEVEL RIDGE OVER THE YUKON TERRITORY AND EASTERN ALASKA. DEVELOPMENT OF SUCH A RIDGE OFTEN LEADS TO PRONOUNCED WARMING OVER THE INTERIOR AND CAN INITIATE A DYNAMIC BREAKUP WITH POTENTIAL ICE JAM FLOODING. WITHOUT AN INDICATION OF A SIGNIFICANT WARMING TREND BREAKUP ACROSS ALASKA IS LIKELY TO BE 2-4 DAYS LATER THAN AVERAGE. FOR MORE INFORMATION ON THE OUTLOOKS FOR THIS SPRING PLEASE REFER TO THE CLIMATE PREDICTION CENTER WEB SITE AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/FORECASTS. THE FOLLOWING TABLE GIVES AN ESTIMATION OF FLOOD POTENTIAL FOR VARIOUS LOCATIONS AROUND THE STATE AND 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. * AVERAGE BREAKUP DATES ARE FOR THE PERIOD 1970 THROUGH 2010 AND ARE CALCULATED FOR LOCATIONS WITH AT LEAST 5 YEARS OF DATA. --------------------------------------------------------------------- SNOWMELT FLOOD AVERAGE NO. OF FORECAST RIVER - REACH RUNOFF POTENTIAL BREAKUP YEARS BREAKUP VOLUME DATE * RECORD DATE ------------- ---------- --------- ------- ------ -------- SOUTHEAST PANHANDLE AVERAGE KENAI RIVER BELOW ANCHOR RIVER BELOW MATANUSKA RIVER BELOW SUSITNA RIVER BELOW GOLD CREEK LOW SUNSHINE LOW 05/01 21 5/02-5/09 YENTNA RIVER BELOW LAKE CREEK LOW 05/01 20 5/01-5/07 SKWENTNA RIVER BELOW SKWENTNA LOW 04/30 17 5/01-5/07 COPPER RIVER BASIN BELOW GAKONA RVR @ HWY HIGH 04/30 25 5/01-5/09 GULKANA RVR @ HWY LOW 04/30 23 5/01-5/07 CHENA RIVER AVERAGE CHENA LAKES PROJECT LOW FAIRBANKS LOW 04/26 25 4/28** TANANA RIVER BELOW NORTHWAY LOW 04/23 25 4/29-5/04 SALCHA LOW-MOD FAIRBANKS LOW 04/29 13 5/01-5/06 NENANA LOW 05/02 37 5/03-5/09 MANLEY LOW 05/03 19 5/05-5/14 KUSKOKWIM RIVER BELOW NIKOLAI LOW 04/23 26 4/24** MCGRATH LOW-MOD 05/07 37 5/08-5/15 STONY RIVER LOW 05/06 23 5/06-5/13 SLEETMUTE LOW-MOD 05/05 22 5/05-5/12 RED DEVIL LOW-MOD 05/06 25 5/06-5/13 CROOKED CREEK LOW-MOD 05/07 25 5/07-5/14 ANIAK LOW-MOD 05/07 28 5/07-5/14 KALSKAG LOW-MOD 05/08 22 5/08-5/15 TULUKSAK LOW-MOD 05/09 19 5/10-5/17 AKIAK LOW-MOD 05/10 25 5/10-5/18 KWETHLUK MOD BETHEL LOW-MOD 05/12 40 5/13-5/20 NAPAKIAK LOW-MOD 05/12 17 5/13-5/20 YUKON RIVER (UPPER) AVERAGE DAWSON, YT LOW 05/06 41 5/07-5/13 EAGLE LOW 05/05 31 5/06-5/12 CIRCLE LOW-MOD 05/09 29 5/10-5/16 FORT YUKON LOW 05/10 28 5/11-5/17 BEAVER LOW 05/10 16 5/12-5/18 STEVENS VILLAGE LOW 05/11 16 5/13-5/19 RAMPART LOW 05/12 17 5/13-5/19 YUKON RIVER (MIDDLE) AVERAGE TANANA LOW 05/10 26 5/11-5/17 RUBY LOW 05/11 27 5/13-5/19 GALENA LOW-MOD 05/12 28 5/13-5/19 KOYUKUK LOW-MOD NULATO LOW-MOD 05/12 15 5/13-5/19 KALTAG LOW 05/14 35 5/15-5/21 ANVIK LOW 05/16 24 5/17-5/23 YUKON RIVER (LOWER) AVERAGE HOLY CROSS LOW 05/15 24 5/16-5/22 RUSSIAN MISSION LOW 05/15 26 5/16-5/22 MARSHALL LOW-MOD 05/15 20 5/16-5/22 PILOT STATION LOW 05/17 14 5/18-5/25 MOUNTAIN VILLAGE LOW 05/18 24 5/19-5/26 ALAKANUK/EMMONAK LOW-MOD 05/23 26 5/23-5/30 KOYUKUK RIVER AVERAGE BETTLES LOW 05/09 29 5/11-5/18 ALLAKAKET LOW 05/10 24 5/12-5/18 HUGHES LOW-MOD 05/10 23 5/12-5/18 SEWARD PENINSULA ABOVE BUCKLAND RIVER ABOVE BUCKLAND MOD 05/18 20 5/18-5/26 KOBUK RIVER ABOVE KOBUK MOD 05/16 31 5/17-5/23 SHUNGNAK LOW 05/17 21 5/19-5/25 AMBLER LOW 05/18 28 5/19-5/25 NOATAK RIVER ABOVE NOATAK LOW-MOD 05/20 16 5/21-5/27 BROOKS RANGE - NORTH AVERAGE COLVILLE @ UMIAT LOW 05/25 12 5/23-5/30 COLVILLE @ COLVILLE LOW 06/01 14 5/30-6/06 FOR MORE DETAIL AND TO SEE A FLOOD POTENTIAL MAP REFER TO OUR WEB SITE AT HTTP://APRFC.ARH.NOAA.GOV. ...THIS IS THE LAST SPRING BREAKUP OUTLOOK FOR THE SEASON. FOR MORE INFORMATION REFER TO THE SPRING BREAKUP SUMMARY. $$ SDL