FGAK78 PACR 282241 ESFAK AKZALL-012300- HYDROLOGIC OUTLOOK NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK 240 PM ADT TUE APR 28 2009 ...SPRING BREAKUP OUTLOOK FOR ALASKA... A STRONG UPPER LEVEL RIDGE HAS BECOME WELL ESTABLISHED OVER THE ALASKA-YUKON BORDER. THIS RIDGE WILL BEGIN TO ELONGATE OVER MAINLAND ALASKA. VERY WARM TEMPERATURES AND HIGH FREEZING LEVELS WILL PERSIST FOR MUCH OF THE STATE FOR THE NEXT WEEK. HIGH TEMPERATURES MAY BE 15 TO 20 DEGREES ABOVE NORMAL WITH MANY WARMER LOCATIONS REACHING INTO THE 70'S. WITH EXTENSIVE SNOW COVER STILL PRESENT THERE WILL BE A SIGNIFICANT INCREASE IN SNOWMELT RUNOFF. RISES IN STREAM LEVELS COULD LEAD TO ICE JAM FORMATION IN AREAS WHERE RIVER ICE COVER IS STILL INTACT. A DYNAMIC BREAKUP IS EXPECTED THIS YEAR WITH A HIGHER THAN NORMAL CHANCE OF ICE JAMS AND ASSOCIATED FLOODING. THE FLOOD POTENTIAL FROM SNOWMELT AND ICE JAMS THIS SPRING BREAKUP SEASON THROUGHOUT ALASKA IS CURRENTLY RATED AS MODERATE TO HIGH IN ALL LOCATIONS THAT ARE PRONE TO FLOODING FROM ICE JAMS DURING BREAKUP. FLOOD POTENTIAL FOR OTHER LOCATIONS REMAINS AS LOW OR LOW TO MODERATE. BREAKUP WAS INITIALLY EXPECTED TO BE LATER THAN NORMAL THIS YEAR BUT THE PROLONGED PERIOD OF WARM TEMPERATURES MAY PUSH BREAKUP DATES CLOSER TO NORMAL. THIS FORECAST IS BASED ON OBSERVED SNOWPACK...ICE THICKNESS REPORTS AND LONG RANGE TEMPERATURE FORECASTS. ICE - APRIL 1ST ICE THICKNESSES SUGGEST SLIGHTLY BELOW NORMAL THICKNESSES FOR SOUTHCENTRAL ALASKA... NEAR NORMAL IN THE FAIRBANKS VICINITY... AND ABOVE NORMAL ALONG THE YUKON BORDER AND SOUTHWEST ALASKA. ICE THICKNESS CONDITIONS HAVE NOT CHANGED SIGNIFICANTLY DUE TO OVERALL COOLER TEMPERATURES FOR THE FIRST HALF OF APRIL. AS OF APRIL 1ST... THE YUKON RIVER AT EAGLE HAD 138% OF NORMAL ICE THICKNESS. THE KUSKOKWIM RIVER ICE AT MCGRATH AND BETHEL WERE ABOUT 120% OF NORMAL THICKNESS. ACCUMULATED FREEZING DEGREE DAYS DURING APRIL HAVE GENERALLY BEEN ACCUMULATING AT AN ABOVE NORMAL RATE AND WINTER SEASON VALUES ARE BETWEEN 105 AND 130 PERCENT OF NORMAL ACROSS MOST OF MAINLAND ALASKA. ACROSS THE NORTH SLOPE ACCUMULATED FREEZING DEGREE DAYS ARE SLIGHTLY BELOW NORMAL WITH BARROW AT 87 PERCENT. SNOW - AN ANALYSIS OF THE APRIL 1 SNOWPACK BY THE NATURAL RESOURCES CONSERVATION SERVICE (NRCS) INDICATED NORMAL TO ABOVE NORMAL SNOWPACK THROUGHOUT MUCH OF THE WESTERN HALF OF THE STATE... AND THE ENTIRE YUKON RIVER DRAINAGE... SOUTHEAST ALASKA... AND THE COPPER RIVER. THE UPPER YUKON IN CANADA AS WELL AS MANY BASINS IN SOUTHEAST ALASKA HAD GREATER THAN 150% OF NORMAL SNOWPACK. THE KENAI PENINSULA IS BELOW TO WELL BELOW NORMAL. NORTH SLOPE DRAINAGES FROM DEADHORSE WEST WERE BELOW NORMAL. REGARDLESS OF CLIMATE AVERAGES THERE IS ENOUGH SNOW IN MOST AREAS TO PRODUCE SIGNIFICANT SNOWMELT RUNOFF PEAKS IF SUBJECTED TO A RAPID WARMING PATTERN. FOR MORE DETAILS ON THE APRIL 1 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://AMBCS.ORG AND SELECT SNOWPACK REPORTS OR SNOWPACK MAPS. MAY 1 DATA WILL BECOME AVAILABLE IN EARLY MAY. WEATHER - ALMOST ALL OF ALASKA WAS COLDER THAN NORMAL DURING THE MONTH OF MARCH WITH MOST LOCATIONS AVERAGING BETWEEN 3 AND 5 DEGREES COOLER THAN NORMAL. THIS TREND CONTINUED THROUGH THE FIRST TWO WEEKS OF APRIL... THOUGH RECENT TEMPERATURES HAVE BEEN NEAR TO ABOVE NORMAL. THE STRONG UPPER LEVEL RIDGE OVER THE ALCAN BORDER WILL BRING NEAR RECORD HIGH TEMPERATURES AND FREEZING LEVELS OVER 10000 FT TO PORTIONS OF THE EASTERN INTERIOR. AS WARM TEMPERATURES SPREAD WESTWARD ACROSS THE MAINLAND A DYNAMIC BREAKUP IS EXPECTED TO BEGIN WITH A HIGHER THAN NORMAL CHANCE OF ICE JAMS AND ASSOCIATED FLOODING. PLEASE REFER TO THE CLIMATE PREDICTION CENTER WEB SITE AT HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/FORECASTS FOR UPDATED OUTLOOKS. 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 2008 AND ARE CALCULATED FOR LOCATIONS WITH AT LEAST 5 YEARS OF DATA. ** ACTUAL BREAKUP DATE FOR 2009 --------------------------------------------------------------------- SNOWMELT FLOOD AVERAGE NO. OF FORECAST RIVER - REACH RUNOFF POTENTIAL BREAKUP YEARS BREAKUP VOLUME DATE * RECORD DATE ------------- ---------- --------- ------- ------ -------- SOUTHEAST PANHANDLE ABOVE KENAI RIVER BELOW ANCHOR RIVER BELOW MATANUSKA RIVER AVERAGE SUSITNA RIVER AVERAGE GOLD CREEK LOW SUNSHINE LOW 05/03 19 4/30-5/05 YENTNA RIVER AVERAGE LAKE CREEK LOW-MOD 04/30 18 4/28-5/02 SKWENTNA RIVER AVERAGE SKWENTNA LOW-MOD 04/30 15 4/28-5/02 COPPER RIVER BASIN AVERAGE GAKONA RVR @ HWY LOW 04/30 23 4/28-5/04 GULKANA RVR @ HWY LOW 04/29 21 4/28-5/02 CHENA RIVER AVERAGE CHENA LAKES PROJECT LOW-MOD FAIRBANKS LOW-MOD 04/25 23 4/28-4/29 TANANA RIVER AVERAGE NORTHWAY LOW 04/23 23 4/27** SALCHA HIGH FAIRBANKS LOW-MOD 04/30 11 4/29-5/04 NENANA LOW 05/02 35 5/01-5/06 MANLEY LOW-MOD 05/03 17 4/28-5/11 KUSKOKWIM RIVER ABOVE NIKOLAI LOW 04/23 24 4/25** MCGRATH MODERATE 05/07 35 5/05-5/12 STONY RIVER LOW 05/06 21 5/04-5/10 SLEETMUTE MOD-HIGH 05/05 20 5/03-5/09 RED DEVIL MOD-HIGH 05/06 23 5/04-5/10 CROOKED CREEK MOD-HIGH 05/07 23 5/05-5/12 ANIAK MOD-HIGH 05/07 26 5/05-5/13 KALSKAG MODERATE 05/07 20 5/06-5/13 TULUKSAK MODERATE 05/09 17 5/08-5/15 AKIAK MODERATE 05/10 23 5/08-5/16 KWETHLUK MOD-HIGH BETHEL MODERATE 05/12 38 5/11-5/18 NAPAKIAK MODERATE 05/12 15 5/11-5/18 YUKON RIVER (UPPER) ABOVE DAWSON, YT 05/06 39 5/04-5/10 EAGLE MODERATE 05/05 29 5/03-5/09 CIRCLE MOD-HIGH 05/09 27 5/07-5/13 FORT YUKON LOW-MOD 05/10 26 5/08-5/14 BEAVER LOW 05/11 14 5/09-5/15 STEVENS VILLAGE LOW 05/12 14 5/10-5/16 RAMPART LOW 05/13 15 5/11-5/17 YUKON RIVER (MIDDLE) ABOVE TANANA LOW 05/10 24 5/08-5-14 RUBY LOW 05/12 25 5/10-5/16 GALENA MOD-HIGH 05/12 26 5/10-5/16 KOYUKUK MOD-HIGH NULATO MOD-HIGH 05/13 13 5/11-5/17 KALTAG LOW 05/14 33 5/12-5/18 ANVIK LOW-MOD 05/17 22 5/15-5/22 YUKON RIVER (LOWER) ABOVE HOLY CROSS LOW 05/16 22 5/15-5/21 RUSSIAN MISSION LOW-MOD 05/15 24 5/14-5/21 MARSHALL MODERATE PILOT STATION LOW 05/17 12 5/15-5/23 MOUNTAIN VILLAGE LOW 05/18 22 5/16-5/24 ALAKANUK/EMMONAK MOD-HIGH 05/22 26 5/21-5/28 KOYUKUK RIVER ABOVE BETTLES LOW 05/10 27 5/07-5/15 ALLAKAKET LOW-MOD 05/11 22 5/08-5/15 HUGHES MODERATE 05/11 21 5/08-5/15 SEWARD PENINSULA ABOVE BUCKLAND RIVER ABOVE BUCKLAND MOD-HIGH 05/18 18 5/15-5/24 KOBUK RIVER ABOVE KOBUK MODERATE 05/16 29 5/14-5/21 SHUNGNAK LOW 05/18 19 5/16-5/23 AMBLER LOW 05/18 26 5/16-5/23 NOATAK RIVER ABOVE NOATAK LOW 05/20 14 5/17-5/25 BROOKS RANGE - NORTH BELOW COLVILLE @ UMIAT LOW 05/25 11 5/21-5/29 COLVILLE @ COLVILLE LOW 05/31 11 5/27-6/05 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 MAY 1. $$ BCB