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Seasonal Forecasting 101

Seasonal Forecasting 101. Dan Leonard dleonard@wsi.com. Dr. Todd Crawford tcrawford@wsi.com. Weather Forecasting and the Markets. Energy Trading Natural Gas, Oil and Power Wind/Hydro/Solar Commodities Insurance. Seasonal Forecasting and Market Impacts . w inter forecasts issued.

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Seasonal Forecasting 101

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  1. Seasonal Forecasting 101 • Dan Leonard • dleonard@wsi.com • Dr. Todd Crawford • tcrawford@wsi.com

  2. Weather Forecasting and the Markets • Energy Trading • Natural Gas, Oil and Power • Wind/Hydro/Solar • Commodities • Insurance

  3. Seasonal Forecasting and Market Impacts winter forecasts issued • Traders initially hopeful for cold winter • Slow downward trend in price once reality of warmweather sets in

  4. Updated Forecast Impact on the Markets Updated morning forecasts trend colder Midday models follow through • Numerical computer models and medium range forecast changes can play a major role in short term prices

  5. Seasonal Forecasting @ WSI - Methodology • Dynamical Climate Forecasting Model (NCAR CCM3.6) • Run @ WSI • Coarse resolution (2.5 x 2.5 deg), driven by initial ocean temp • anomalies • 2 versions of model, complementary skill • 8 runs (ensemble) per model version to further increase skill • Ensemble mean is most skillful forecast • 3 Proprietary Statistical Models • Based on historical relationships between • indices & weather • Singular/Multivariate regression, analog

  6. Statistical Models ENSO Stat Model A Solar Cycle Snow Cover Stat Model B PDO Stat Model C Index 20

  7. Seasonal Forecast Process Final Climate Model Output Climate Model v1 (raw) Post-process Blend all Inputs Climate Model v2 (raw) Post-process Stat Model 2 Stat Model 3 Human touch Stat Model 4 WSI Final Forecast

  8. Seasonal Forecasting @ WSI – Overview • Forecasts issued for US and Europe • US forecasts issued twice-monthly • Tuesday mid-month (between 13th-19th) • Last trading day of month • Temperature and precip forecasts produced • Next three calendar months (Feb, Mar, Apr) • Next two seasons (FMA, MAM) • Tabular, graphical, and discussion format

  9. Seasonal Forecasting Tools - Skill Models have similar skill WSI Forecasts (October 2000-present) 64%

  10. So, What is “Normal” in an Ever-Changing Climate? • 30-year normals are typically used since Atlantic/Pacific cycles • are on multidecadal time scales • But these are only updated once a decade, mainly for convenience • No reason why you can’t use 13, 26, or 36 year normals if they work better! • Historically, which normals have worked best at predicting near-term temps?

  11. Which Normals are Best to Use Going Forward? Using standard 30-year even worse! 15-20 years: Recent trends, solar cycle? 40-45 years: Pacific cycle 60 years: Atlantic cycle Using standard 30-yr avg (changes once every 10 years) is even worse than using trailing 30-yr avg

  12. New 30-yr normals (1981-2010 replaces 1971-2000) New Normals Warmer Most Locations, Especially during Winter Summer Winter

  13. Near-Term: Summer Temps Warming, Winter Cooling? US Winter Temps US Summer Temps

  14. Weather More Volatile Now? “We’ve just had two consecutive top-5 warmest summers and two consecutive top-10 coldest winters. Are these sorts of extremes the new normal?” ,1937 - September 15

  15. Trend Towards Hotter Summers • The last 2 winters in the US hottest back-to-back summers on record • 2011 2nd hottest summer on record, just behind 1936

  16. Atlantic Multi-decadal oscillation (AMO) • Example of a positive phase of the AMO • Tripole of water temp anomalies

  17. Atlantic Ocean pattern dictates US summer temperatures • Atlantic Multi-decadal Oscillation

  18. Trend Towards Colder Winters • The last 5 winters in the US have been colder (in aggregate) than the long-term • NCDC normals (1895-2010) • This is the first time this has occurred since the  winters of 1983/84 to 1987/88 • The “new normal”? 

  19. Pacific Decadal Oscillation (PDO) + - • PDO pattern displays a “horseshoe” effectin the SST anomalies, with cold temps bounded • by warm temps to the south, east and north

  20. The PDO/PNA connection • A positive PDO favors the development of a positive Pacific/North America pattern (+PNA)

  21. Pacific Ocean pattern plays major role in US winter temps Last cold winter regime 1950s-1970s

  22. North Atlantic Oscillation (NAO) Negative Phase NAO Cold northerly flow into US Arctic air masses descend from north Colder eastern/central US Positive Phase NAO Mild westerly flow dominates Arctic air remains north Warmer eastern/central US

  23. North Atlantic Oscillation (NAO) • NAO describes the strength • of the polar vortex • Strong vortex (pos NAO) = • stronger Atl jet stream • Weak vortex (neg NAO) = • N Atl blocking, tapping Arctic air • Last two winters have had • extremely negative NAO

  24. NAO Correlations, Winter vsSummer Summer Winter • Subtropical ridge tends to be more active in the summer

  25. NAO clearly strongly related to US winter temps

  26. Mid-latitude October Atlantic SSTs modulate NAO Increased SST gradient = Enhanced polar jet Decreased SST gradient = Weaker/amplified polar jet +AMO lends -NAO regime -AMO lends +NAO regime

  27. Solar cycle minima enhance negative NAO

  28. Solar Cycles Through History • Hadley Centre (UK) oldest continuous temp measurements • Little Ice Age (1600s) occurred during solar blackout • Other cooling during solar minima in 1810s, 1900s, 1960s • Recent solar cycle weakest in at least 100 years

  29. Siberian Snow Cover – NAO correlations Asian snow cover build in October Impacts complex dynamic processes (Cohen et al.) that modulate blocking frequency/intensity Pattern most sensitive to snow build in October due to rapidly increasing potential energy source as poles darken/cool Data suggests snow cover most important during weeks 41-44 (October)

  30. Sudden stratospheric warmings drive negative NAO In about half of all winters, dynamical processes produce a sudden and extreme warming of stratosphere (SSW) This warming often propagates back down to the polar surface, resulting in long-lived negative NAO events Ability to predict whether a SSW event will occur in key to predicting winter NAO Have had SSW events in 8 of last 10 winters

  31. NAO Review • Primary NAO Drivers • AMO • Solar Activity • Siberian Snowcover in OCT • SSWs

  32. El Nino Forcing WARM Tropical convection enhanced over warmest SSTs – ridging poleward and downstream

  33. La Nina Impacts • Cold water associated with La Nina • focuses tropical convection • (t-storms) over • Indian Ocean/Indonesia • Focused convection produces • downstream and poleward response • at mid-latitudes over North Pacific • and western US • Dateline ridging guides Arctic air into • western Canada & western US Aggregate 500 mb pattern for last 14 mod/strong La Nina events

  34. La Nina Seasonal Impacts – DJF Temperature Strongest cold signal: 11 of 15 events below-normal in north-central US Strongest warm signal: 13 of 15 events above-normal in south-central US Aggregate temp. anom. pattern for last 15 mod/strong La Nina events

  35. Colder winters recently, regardless of ENSO state… ‘10-’11 ‘09-’10 ‘08-’09 Strong La Nina Strong El Nino Weak La Nina • Last 3 winters coldest stretch since mid-1980s! • Typical ENSO correlations failed the last 2 years

  36. Pacific Decadal Oscillation (PDO) + - • PDO pattern displays a “horseshoe” effectin the SST anomalies, with cold temps bounded • by warm temps to the south, east and north

  37. If PDO/ENSO out of phase, textbook signal is gone El Nino with negative PDO El Nino with positive PDO

  38. La Nina Stratified by NAO Phase La Nina + Positive NAO La Nina + Negative NAO • Cold north/west, warm south La Nina signal • NAO provides offset to eastern/central US temps

  39. The Bottom Line • ENSO taken alone is a poor predictor of seasonal variability over the lower 48 • NAO and PNA, although more difficult to predict, have a much stronger seasonal correlation

  40. Winter 07-08: A Winning Season

  41. Directionally Correct

  42. 2011-2012 Forecast • October forecast called for a cold winter north, especially in January

  43. A December Disaster Sometimes Things Don’t Work Out According to Plan

  44. Rationale in October • Positive signs for a cold winter north… Historically Low Arctic Sea Ice Accelerating Snow Cover Build Strong Negative Pacific Decadal Oscillation Warm North Atlantic (positive AMO) Emerging La Nina Event

  45. Possible Wild Card: Different Tropical Pacific Convection Than 2010? Warmer Indian Ocean, cooler Indonesia this year More MJO phase 2/3 (warmer) activity this winter? ?

  46. Tropical Convection shifts east with time -MJO starts the season over the Indian Ocean but eventually Progresses to a more typical Nina position over Indonesia

  47. Pacific Not to Blame Don’t look at me!! LA NIÑA Mean Ridge Axis Persistent Convection Classic –PDO/Nina setup

  48. Look to the Atlantic/Arctic… • Split flow pattern inthe west • Very strong polar vortex • Fast, zonal regimenorthern tier of the US

  49. 2011-12 NAO: Positively Awful • NAO has beenpositive since midNovember • Most positive NAO ever inDecember

  50. State of the Stratosphere • Stratosphere has been colder than normal so far,indicating a strong polar vortex

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