FGAK78 PACR 302159 ESFAK AKZALL-012300- HYDROLOGIC OUTLOOK NWS ALASKA PACIFIC RIVER FORECAST CENTER ANCHORAGE AK 2 PM ADT WED APR 30 2008 ...SPRING BREAKUP OUTLOOK FOR ALASKA... ...THIS IS THE LAST BREAKUP OUTLOOK FOR THE SEASON. THE SPRING BREAKUP SUMMARY IS SCHEDULED TO START UP AT 2 PM THURSDAY MAY 1... THE FLOOD POTENTIAL FOR ALASKA FROM SNOWMELT AND ICE JAMS THIS SPRING BREAKUP SEASON IS RATED AS AVERAGE. HOWEVER LOCATIONS IN WESTERN ALASKA HAVE AN ABOVE AVERAGE ICE JAM FLOOD POTENTIAL BASED ON CURRENT SNOW AND RIVER ICE CONDITIONS AND LONG RANGE TEMPERATURE FORECASTS. ICE - APRIL 1 ICE THICKNESS DATA ARE AVAILABLE FOR A LIMITED NUMBER OF OBSERVING SITES IN ALASKA. MEASUREMENTS INDICATE THAT ICE THICKNESS RANGED FROM BELOW NORMAL IN SOUTHWEST AND SOUTHCENTRAL ALASKA TO ABOVE NORMAL IN THE NORTH CENTRAL INTERIOR AND THE NORTH SLOPE. ACCUMULATED FREEZING DEGREE DAYS DURING APRIL HAVE GENERALLY BEEN ACCUMULATING AT A NORMAL RATE FOR THIS TIME OF YEAR AND ARE NOW BETWEEN 75 AND 115 PERCENT OF NORMAL WITH THE HIGHEST PERCENTAGE IN SOUTHWEST ALASKA. GENERALLY ICE THICKNESSES ARE GREATER IN AREAS OF THE STATE WITH LESS SNOWPACK. 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 KENAI PENINSULA...AND SOUTHEAST ALASKA. SOME BASINS IN SOUTHERN SOUTHEAST ALASKA HAD GREATER THAN 150% OF NORMAL SNOWPACK. THE EASTERN HALF OF THE STATE INCLUDING THE SUSITNA...COPPER...TANANA...YUKON ABOVE TANANA...UPPER KOYUKUK AND NORTH SLOPE DRAINAGES WERE BELOW TO WELL BELOW NORMAL SNOWPACK. SNOW AND RAIN DURING MARCH AND EARLY APRIL HAVE BEEN HEAVIEST ALONG THE GULF OF ALASKA COASTAL MOUNTAINS. DURING THE PAST WEEK TEMPERATURES MODERATED OVER MUCH OF THE STATE CAUSING LOW ELEVATION SNOW PACK TO DECREASE. HOWEVER, SATELLITE IMAGES STILL SHOW ALMOST COMPLETE COVERAGE ACROSS ALL OF THE WESTERN INTERIOR. COOLER THAN NORMAL TEMPERATURES AND MORE SNOW IS EXPECTED THROUGH THE LAST COUPLE DAYS OF APRIL. BASED ON CURRENT SNOW CONDITIONS IN WESTERN ALASKA THERE IS AN ELEVATED RISK OF FLOODING AT NUMEROUS LOCATIONS ON THE KUSKOKWIM AND AT BUCKLAND AND KOBUK IN NORTHWEST ALASKA. ELSEWHERE THERE IS ENOUGH SNOW TO PRODUCE SIGNIFICANT RUNOFF PEAKS IF SUBJECTED TO A RAPID WARMING TREND. 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 - MOST OF ALASKA WAS COOLER TO MUCH COOLER ON AVERAGE DURING THE LAST 4 WEEKS. AIR TEMPERATURES ARE EXPECTED TO REMAIN COOLER THAN NORMAL OVER MOST OF THE STATE THROUGH THE END OF THE WEEK. MORE NORMAL TO SLIGHTLY ABOVE NORMAL TEMPERATURES ARE EXPECTED BY LATE WEEK IN THE EASTERN INTERIOR HOWEVER THE SOUTHWEST PART OF THE STATE IS EXPECTED TO BE BELOW NORMAL. FREEZING LEVELS ALSO BEGIN TO INCREASE TO OVER 5000 FEET BY THE END OF THE WEEK ACROSS THE EASTERN INTERIOR THE GREATEST FACTOR IN DETERMINING THE SEVERITY OF BREAKUP REMAINS THE WEATHER DURING THE NEXT TWO TO THREE WEEKS. IF A SIGNIFICANT PERIOD OF WARMER THAN NORMAL AIR TEMPERATURES OCCUR RUNOFF GENERATED FROM SNOWMELT WILL LIKELY INITIATE A MECHANICAL BREAKUP ON INTERIOR RIVERS. 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 2007 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 * RECORD DATE ------------- ---------- --------- ------- ------ -------- SOUTHEAST PANHANDLE ABOVE KENAI RIVER AVERAGE ANCHOR RIVER AVERAGE MATANUSKA RIVER BELOW SUSITNA RIVER BELOW GOLD CREEK LOW SUNSHINE LOW 05/03 18 5/03-5/08 YENTNA RIVER AVERAGE LAKE CREEK LOW 04/30 17 5/02-5/05 SKWENTNA RIVER AVERAGE SKWENTNA LOW 04/30 14 5/01-5/04 COPPER RIVER BASIN AVERAGE GAKONA RVR @ HWY LOW 04/30 22 5/02-5/07 GULKANA RVR @ HWY LOW 04/29 20 5/02-5/06 CHENA RIVER BELOW CHENA LAKES PROJECT LOW FAIRBANKS LOW 04/25 22 4/29** TANANA RIVER BELOW NORTHWAY LOW 04/23 22 4/26** SALCHA LOW-MOD FAIRBANKS LOW 04/28 11 5/02-5/06 NENANA LOW 05/02 34 5/03-5/07 MANLEY LOW 05/03 16 5/04-5/09 KUSKOKWIM RIVER AVERAGE NIKOLAI LOW 04/23 23 4/26** MCGRATH MOD 05/07 34 5/07-5/14 STONY RIVER LOW 05/06 20 5/05-5/13 SLEETMUTE MOD 05/05 19 5/04-5/11 RED DEVIL MOD 05/06 22 5/05-5/12 CROOKED CREEK MOD 05/07 22 5/06-5/13 ANIAK MOD 05/07 25 5/06-5/13 KALSKAG LOW-MOD 05/07 19 5/06-5/14 TULUKSAK LOW-MOD 05/09 16 5/08-5/17 AKIAK LOW-MOD 05/10 22 5/09-5/17 KWETHLUK MOD BETHEL LOW-MOD 05/12 37 5/12-5/19 NAPAKIAK LOW-MOD 05/12 14 5/11-5/19 YUKON RIVER (UPPER) BELOW EAGLE LOW 05/05 28 5/02-5/08 CIRCLE LOW-MOD 05/09 26 5/06-5/12 FORT YUKON LOW 05/10 25 5/07-5/13 BEAVER LOW 05/11 13 5/08-5/14 STEVENS VILLAGE LOW 05/12 13 5/09-5/15 RAMPART LOW 05/13 14 5/10-5/16 YUKON RIVER (MIDDLE) BELOW TANANA LOW 05/10 23 5/07-5-13 RUBY LOW 05/12 24 5/09-5/15 GALENA LOW-MOD 05/12 25 5/09-5/15 KOYUKUK LOW-MOD NULATO LOW-MOD 05/13 12 5/10-5/16 KALTAG LOW 05/14 32 5/11-5/17 ANVIK LOW 05/17 21 5/14-5/21 YUKON RIVER (LOWER) BELOW HOLY CROSS LOW 05/15 21 5/12-5/18 RUSSIAN MISSION LOW 05/15 23 5/12-5/19 PILOT STATION LOW 05/17 11 5/13-5/21 MOUNTAIN VILLAGE LOW 05/18 21 5/14-5/22 ALAKUNUK/EMMONAK LOW-MOD 05/22 25 5/19-5/26 KOYUKUK RIVER AVERAGE BETTLES LOW 05/10 26 5/07-5/14 ALLAKAKET LOW 05/11 21 5/08-5/14 HUGHES LOW 05/11 20 5/08-5/14 SEWARD PENINSULA ABOVE BUCKLAND RIVER ABOVE BUCKLAND MOD-HIGH 05/19 16 5/16-5/24 KOBUK RIVER ABOVE KOBUK MOD-HIGH 05/17 27 5/15-5/22 SHUNGNAK LOW 05/19 17 5/17-5/24 AMBLER LOW 05/19 24 5/17-5/24 NOATAK RIVER ABOVE NOATAK LOW 05/20 13 5/16-5/24 BROOKS RANGE - NORTH BELOW COLVILLE @ UMIAT LOW 05/25 10 5/21-5/29 COLVILLE @ COLVILLE LOW-MOD 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. THIS IS THE LAST BREAKUP OUTLOOK FOR THE SEASON. THE SPRING BREAKUP SUMMARY IS SCHEDULED TO START UP AT 2 PM THURSDAY MAY 1. $$ JHC