Alaska River Breakup: Historic Comparison and 2017 Spring Outlook. Crane Johnson and Rick Thoman NaConal Weather Service April 11 th 2017

Transcription

1 Alaska River Breakup: Historic Comparison and 2017 Spring Outlook Crane Johnson and Rick Thoman NaConal Weather Service April 11 th 2017

2 Outline Ø Breakup process Ø Recap of 2016 Alaska Breakup Ø Current 2017 condicons Ø Climate Outlook Ø A look at trends: past, present and future Ø Spring 2017 Breakup Outlook 2

3 Types of Breakup Process Dynamic breakup Ø Ice remains hard and resistant to breaking up Ø Ice moves when pushed by ice from upstream Ø Ice jams form that can cause upstream flooding Ø Extreme cases are Kenai River in January 1969 and January 2007 and Yukon River in May 2009 and Most Breakups are a Blend Thermal breakup Ø Ice becomes very roven (candled) before ice from upstream arrives Ø RoVen ice is weak and has less resistance to breaking into very small pieces Ø No significant ice jams form Ø Extreme case would occur with very livle snow melt inflow and warm sunny weather to rot the 3

4 Breakup Overview Thermal transicon from an ice covered river to icefree open water Napaskiak, April 12 th

5 Breakup Overview Dynamic or Mechanical transi=on from an ice covered river to ice-free open water Bishop Rock May 27, 2013 Galena Flooding May 28,

6 Ice Jam LocaCons in Alaska 6

7 When is breakup? The breakup front is the interface between sta=onary and moving ice sheets Flow Direc=on 7

8 When is breakup? Or.. Bethel Alaska 8

9 Recap of 2016 = Snow Covered Ø Generally below average snowpack for most of the state. Ø Large porcons of the state were snow free by mid April Alaska Snow Coverage April 10 th,

10 Recap of 2016 Ø Above average JFM temperatures throughout the state. Ø April 1 st measured ice thicknesses were below average for most areas in the State. January March Temperatures 10

11 Recap of Timing Compared to the average ( ), breakup in 2016 was extremely early with many loca=ons experiencing a record early breakup. 11

12 Recap of Severity Ø Deering Moderate Flooding Ice jam on the Inmachuk River flooded the access road to the airport Ø Eagle Minor Flooding Ice jam formed on the Yukon River approximately 10 miles downstream from Eagle Ø Sag River No significant flooding 12

13 2017 Current CondiCons 13

14 2017 Snow Coverage = Snow Covered 14

15 2017 Winter Temperatures 15

16 2017 Winter Temperatures Normal Normal 2014 &

17 April Ice Thickness Measurements 81% 105% 131% 105% 118% 118% 105% 85%-121% 161% 112% 126% 107%-127% 17

18 2016/2017 Winter Ice Anomalies Ø Mid winter ice jam on the Kenai River No flooding Ø Northslope Normal aufeis condicons reported on the Sag River Ø Good Winter Travel CondiCons Ø Notably un-evenhul river ice condicons around the state Kenai River January 4 th

19 Sag River Aufeis CondiCons 19

20 Sag River Aufeis CondiCons 04/06/

21 Climate Outlook For Spring 2017 Ø Quick Review of current climate system state Ø Week 2 (later April) Ø Week 3-4 (late April to early May) Ø Monthly (May and June) Ø Break-up Dates and oceanic indices 21

22 Where we re at now Ø Snowpack bever than last year, but locally very low Ø La Niña ended in March Ø Niño 4 region SSTs near normal Ø Near normal Gulf of Alaska SSTs Ø Below normal Bering Sea ice coverage overall 22

23 Tanana R. at Nenana: Forecast Apr-May Temps and you forecast break-up 23

24 GEFS Reforecast: Week 2 April 18-24,

25 NAEFS ProbabiliCes Accumulated Pcpn 10mm Apr

26 Week 3-4 (late April to early May) CPC Outlook Issued April 07 Climo=CFSv2 hindcast

27 Monthly Outlooks and Date CorrelaCons with Oceanic Indices Ø StaCsCcal Guidance Constructed Analogs West Pacific SSTs and Alaska Temps Ø Dynamic Models NMME Project (Mar 01 run) CFS Recent Runs Ø Using Tanana at Nenana Break-up dates Niño 4 anomalies Break-up vs. PDO Break-up vs. Niño 4 anomalies 27

28 Apr-Jun Temperatures from Global SSTs 28

29 Niño 4 vs. near sfc temp lagged correlaconapr-may (since 1977) 29

30 May 2017 Temp Departure Outlooks Avg Dep ( C) 3-Category Probabili=es Calibrated 3-Category Probs Member Averages 30

31 Recent CFS for May: Tercile Category Probs Climo=CFSv2 hindcast

32 June 2017 Temp Departure Outlooks Avg Dep ( C) 3-Category Probabili=es Calibrated 3-Category Probs Member Averages 32

33 El Niño or La Niña or 33

34 Pacific Decadal OscillaCon Index 34

35 PDO and Breakup Dates 35

36 Niño 4 SSTs and Breakup 36

37 Timing of break-up has changed 37

38 Climate Outlook Summary Ø Current condicons and dynamic models support slightly increased chances for warm April and May Ø Rest of April Clts strongly toward drier than typical Ø StaCsCcal tools for break-up (early vs. late) are inconclusive 38

39 What does that mean? 2017 Breakup Outlook Ø Trending towards a normal breakup year Increased potencal for a dynamic breakup along most major rivers in Alaska Flooding is possible at the typical locacons along all rivers subject to ice jam and snow melt flooding Ø Current outlook is for low likelihood of flooding along the Sag River. The road has been elevated with less aufeis than in previous year. 39

40 Average Breakup Date 5/25 6/4 5/19 5/21 5/20 5/12 5/16 5/11 5/18 5/13 5/6 5/16 5/11 5/8 5/10 4/30 5/5 4/23 5/1 5/3 5/10 5/8 4/29 5/4 5/4 5/2 4/26 Average Breakup Dates Shown 40

41 OUTLOOK IN ORANGE Outlook: 1-3 days early Average Breakup Dates Shown 5/21 Breakup Date Outlook 5/19 5/20 5/12 5/16 5/11 5/18 5/13 5/6 5/16 5/11 5/8 5/25 5/5 4/23 6/4 5/10 4/30 5/3 5/1 Outlook: 2-4 days early Outlook: Average 4/29 5/10 5/8 5/4 5/4 5/2 4/26 Breakup Date outlook based on long range forecasts and subject to change. 41

42 Flood Outlook PotenCal 42

43 2009 Temperature Influence 2012 Spring Temperatures are the biggest driver for ice jam flooding.. 43

44 Temperature Influence

45 Breakup Map 45

46 Tanana at Nenana Yesterday 46

47 Data Sharing. Ø Ø We can follow your social media Ø #Akriverwatch,#AKwx Ø Call: Ø Post an observacon to the LEO Network Ø Submit an observacon to the NWS QuesCons? 47