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