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
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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. 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
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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
