wsi confidential seasonal forecasting 101 dan leonard [email protected] dr. todd crawford...
TRANSCRIPT
WSI CONFIDENTIAL
Weather Forecasting and the Markets
• Energy Trading- Natural Gas, Oil and Power- Wind/Hydro/Solar
• Commodities• Insurance
WSI CONFIDENTIAL
Seasonal Forecasting and Market Impacts
winter forecasts issued
• Traders initially hopeful for cold winter• Slow downward trend in price once reality of warm
weather sets in
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Updated Forecast Impact on the Markets
Updated morning forecasts trend colder
• Numerical computer models and medium range forecast changes can play a major role in short term prices
Midday models follow through
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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
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Statistical Models
ENSO
Solar Cycle
PDO
Snow Cover
Index 20
Stat Model A
Stat Model B
Stat Model C
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Seasonal Forecast Process
Final Climate Model Output
WSI Final Forecast
Climate Model v1(raw)
Stat Model 2
Post-process
Climate Model v2(raw)
Post-process
Human touch
Blend all Inputs
Stat Model 3
Stat Model 4
WSI CONFIDENTIAL
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 producedNext three calendar months (Feb, Mar, Apr)Next two seasons (FMA, MAM)
• Tabular, graphical, and discussion format
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Forecasting Model Skill
Climate Model 57%
Stat Model A 59%
Stat Model B 56%
Stat Model C 59%
Ensemble Mean 61%
Models have similar skill
Seasonal Forecasting Tools - Skill
WSI Forecasts (October 2000-present) 64%
WSI CONFIDENTIAL
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?
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Which Normals are Best to Use Going Forward?
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
Using standard 30-yeareven worse!
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New 30-yr normals (1981-2010 replaces 1971-2000)
Winter Summer
New Normals Warmer Most Locations, Especially during Winter
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Near-Term: Summer Temps Warming, Winter Cooling?
US Winter Temps
US Summer Temps
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Weather More Volatile Now?
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US Summer Temperature Rank
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US Winter Temperature Rank
“We’ve just had two consecutive top-5 warmest summers and two consecutive top-10 coldest winters.Are these sorts of extremes the newnormal?”
- September 15 ,1937
WSI CONFIDENTIAL
• The last 2 winters in the US hottest back-to-back summers on record• 2011 2nd hottest summer on record, just behind 1936
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1.55-Yr Averaged US Summer Temp Anomalies
Ending Year of 5-Yr Period
Trend Towards Hotter Summers
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Atlantic Multi-decadal oscillation (AMO)
• Example of a positive phase of the AMO
•Tripole of water temp anomalies
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Atlantic Ocean pattern dictates US summer temperatures
Atlantic Multi-decadal Oscillation
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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”?
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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
+ -
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The PDO/PNA connection
• A positive PDO favors the development of a positive Pacific/North America pattern (+PNA)
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Pacific Ocean pattern plays major role in US winter temps
Last cold winter regime1950s-1970s
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Positive Phase NAO
Mild westerly flow dominates Arctic air remains north
Warmer eastern/central US
Negative Phase NAO
Cold northerly flow into US Arctic air masses descend from north
Colder eastern/central US
North Atlantic Oscillation (NAO)
WSI CONFIDENTIAL
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
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NAO Correlations, Winter vs Summer
• Subtropical ridge tends to be more active in the summer
Winter Summer
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NAO clearly strongly related to US winter temps
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Mid-latitude October Atlantic SSTs modulate NAO
-AMO lends +NAO regime
Increased SST gradient =Enhanced polar jet
Decreased SST gradient =Weaker/amplified polar jet
+AMO lends -NAO regime
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Solar cycle minima enhance negative NAO
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Solar Cycles Through History
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Hadley Centre CET Winter Temps
• 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
WSI CONFIDENTIAL
Siberian Snow Cover – NAO correlations
Data suggests snow cover mostimportant during weeks 41-44 (October)
Asian snow cover build in October Impacts complex dynamic processes (Cohen et al.) that modulate blocking frequency/intensity
Pattern most sensitive to snow build inOctober due to rapidly increasing potential energy source as poles darken/cool
WSI CONFIDENTIAL
Sudden stratospheric warmings drive negative NAO
In about half of all winters,dynamical processes producea sudden and extreme warmingof stratosphere (SSW)
This warming often propagatesback down to the polar surface, resulting in long-lived negative NAO events
Ability to predict whether a SSW event will occur in key to predictingwinter NAO
Have had SSW events in 8 of last 10 winters
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NAO Review
Primary NAO Drivers
• AMO• Solar Activity• Siberian Snowcover
in OCT• SSWs
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El Nino Forcing
Tropical convection enhanced over warmest SSTs – ridging poleward and downstream
WARM
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La Nina Impacts
Aggregate 500 mb pattern for last 14 mod/strong La Nina events
Focused convection produces downstream and poleward response at mid-latitudes over North Pacific and western US
Dateline ridging guides Arctic air intowestern Canada & western US
Cold water associated with La Ninafocuses tropical convection (t-storms) over Indian Ocean/Indonesia
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La Nina Seasonal Impacts – DJF Temperature
Aggregate temp. anom. pattern for last 15 mod/strong La Nina events
Strongest warm signal:13 of 15 events above-normalin south-central US
Strongest cold signal:11 of 15 events below-normalin north-central US
WSI CONFIDENTIAL
Colder winters recently, regardless of ENSO state…
Last 3 winters coldest stretch since mid-1980s! Typical ENSO correlations failed the last 2 years
‘09-’10‘08-’09 ‘10-’11Strong El Nino Strong La NinaWeak La Nina
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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
+ -
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If PDO/ENSO out of phase, textbook signal is gone
El Nino with positive PDO El Nino with negative PDO
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La Nina Stratified by NAO Phase
La Nina + Negative NAOLa Nina + Positive NAO
Cold north/west, warm south La Nina signal NAO provides offset to eastern/central US temps
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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
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Winter 07-08: A Winning Season
WSI CONFIDENTIAL
Directionally Correct
WSI fcst obsWSI err
WSI dir correct?
Pacific -0.8 -1.0 0.2 YesMountain -0.2 -1.3 1.1 Yes
W. North Central -0.9 -1.5 0.6 YesW. South Central 1.1 2.3 -1.2 YesE. North Central -0.3 0.9 -1.2 NoE. South Central 1.4 2.6 -1.2 Yes
0.2 1.5 -1.3 YesMid-Atlantic 0.3 2.2 -1.9 Yes
1.1 2.9 -1.8 Yes
MAEWSI fcst
1.16
Dir corr 8 of 9
climo fcst 1.80
Anomaly correlation 0.88
WSI CONFIDENTIAL
2011-2012 Forecast
• October forecast called for a cold winter north, especially in January
WSI CONFIDENTIAL
A December Disaster
Sometimes Things Don’t Work Out According to Plan
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Rationale in October
Emerging La Nina Event
Strong Negative Pacific Decadal Oscillation
Warm North Atlantic(positive AMO)
Accelerating Snow Cover Build
Historically Low Arctic Sea Ice
• Positive signs for a cold winter north…
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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??
WSI CONFIDENTIAL
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
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Pacific Not to Blame
LA NIÑA
Don’t look at me!!
Classic –PDO/Nina setup
Persistent Convection
Mean Ridge Axis
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Look to the Atlantic/Arctic…
• Split flow pattern inthe west
• Very strong polar vortex
• Fast, zonal regimenorthern tier of the US
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2011-12 NAO: Positively Awful
• NAO has beenpositive since midNovember
• Most positive NAO ever inDecember
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State of the Stratosphere
• Stratosphere has been colder than normal so far,indicating a strong polar vortex
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Solar Spike
Solar Activity still relatively low but a sudden spike in November
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AMO Index: Missing the Smaller Picture?
Late Oct 2010 Late Oct 2011AMO = +0.367 AMO = +0.103
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• Extreme snow deficit for the north central, NE and Great Basin/NW.
• Positive snowfall anomalies confined to the southern plains and lower Rockies
Snowcover : Unpredictable but Important
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850mbT anom
SfcT anom
Snowless plains and midwest:
• Without snowcover, polar airmasses modify quickly
• Albedo correlation highest in tree-less areas like the plains
Snowcover’s Role in Airmass Modification
WSI CONFIDENTIAL
Hope for a Back End Winter?
Both the GFS and ECMWF depict major SWE developing next week and intensifying during the following week
WSI CONFIDENTIAL
Will the NAO finally flip negative?
-Good NorthAtlantic block
-Still a strong Pacific Jet
-PV is weaker and displaced, but not gone…
WSI CONFIDENTIAL
Latest ECMWF Weekly
-NorthAtlantic block holds through first week of FEB
WSI CONFIDENTIAL
February and March Forecast
-Cold and Stormy North and West
-Warm and dry South
