Products and Services to Support Decision Makers: Forecast Skill, L3MTO, and Beyond 2007 Committee for Environmental Services, Operations, and Research Needs July 19, 2007 Fiona Horsfall NOAA/National Weather Service Climate Services

Outline Climate forecast skillClimate forecast skill Extrapolation of long-term trendsExtrapolation of long-term trends NWS Products: L3MTO, Climate WebsiteNWS Products: L3MTO, Climate Website What’s next?What’s next?

Climate Forecast Skill What do we know? There are important long-term trends in the mean temperature and precipitation climates of North America.There are important long-term trends in the mean temperature and precipitation climates of North America. Primary sources of skill for North AmericaPrimary sources of skill for North America –Trend –ENSO (El Niño-Southern Oscillation) Current models cannot credibly produce future weather scenarios other than the grossest features of the climate. Impact studies based on these are automatically suspect.Current models cannot credibly produce future weather scenarios other than the grossest features of the climate. Impact studies based on these are automatically suspect.

If your cost/loss ratio is small, a tiny bit of forecast skill is adequate for mitigation action.If your cost/loss ratio is small, a tiny bit of forecast skill is adequate for mitigation action. If your cost/loss ratio is higher, you need to look at skill more closely. You should not be using low skill forecasts.If your cost/loss ratio is higher, you need to look at skill more closely. You should not be using low skill forecasts. Climate Forecast Skill When can you use a climate forecast?

Trend

Variations of the Earth’s surface temperature Globalmean14.0°C Trenberth (2004)

Forecast Skill

Heidke Skill ScoreHeidke Skill Score % improvement over expected% improvement over expected Count EC (equal chances) as a hitCount EC (equal chances) as a hit Forecasts become usable with scoreForecasts become usable with score > +25 > +25 Smaller cost/loss ratio – can use lower scoreSmaller cost/loss ratio – can use lower score Hits: Forecasts correct Expected: Climatology Total: Total forecasts Hits – Expected Total - Expected

Climate Forecast Skill Temperature JAS

Climate Forecast Skill Precipitation

SummertimeSummertime –No strong temperature skill for whole country overall –Poor skill for precip in east Reason: trends are weak or noisyReason: trends are weak or noisy Few places around lakes with +2 ins over 30 yearsFew places around lakes with +2 ins over 30 years

What about Global Climate Change? IPCC WG1 Fourth Assessment Report: Summary for Policy Makers A key test for the credibility of a future scenario of any high-impact weather related event is whether all important factors are credibly projected, not just temperatureA key test for the credibility of a future scenario of any high-impact weather related event is whether all important factors are credibly projected, not just temperature –For example Sierra snowpackSierra snowpack Atlantic hurricane activityAtlantic hurricane activity To credibly project something into the future, a model must credibly treat it in the past.To credibly project something into the future, a model must credibly treat it in the past. Bob Livezey

Climate Model Capabilities DJF JJA ? ? ?

Extrapolation of Long-Term Trends Not reasonable without a physical basis.Not reasonable without a physical basis. Existing climate models cannot credibly produce future weather scenarios of other than the gross geographic and seasonal distribution of mean surface temperature.Existing climate models cannot credibly produce future weather scenarios of other than the gross geographic and seasonal distribution of mean surface temperature. This is because they cannot adequately reproduce these scenarios over the recent (30- year) historical record.This is because they cannot adequately reproduce these scenarios over the recent (30- year) historical record.

Regional and Local Products and Services

Local 3-Month Temperature Outlook - L3MTO

L3MTO

L3MTO

L3MTO

L3MTO

L3MTO

L3MTO Formats

L3MTO Probability of Exceedance

Why is L3MTO Useful? If large-scale forecast has skill, uses forecast – downscaled to stationIf large-scale forecast has skill, uses forecast – downscaled to station Adjusts forecast to take into account local climate (micro climates)Adjusts forecast to take into account local climate (micro climates) If no skill in large-scale forecast, adjusts local climatology to incorporate local trendIf no skill in large-scale forecast, adjusts local climatology to incorporate local trend

NOAA Online Weather Data NOWData Data query system for basic climate statistics Data query system for basic climate statistics 19 th Century to yesterday 19 th Century to yesterday 3,800 surface observing stations (non- airport) 3,800 surface observing stations (non- airport) Conterminus U.S., AK, HI, PR, USVI, Guam Conterminus U.S., AK, HI, PR, USVI, Guam Ref: Bob Leffler

NWS Climate Services Download free fact sheets at

And Beyond

Will be Precipitation Local 3-month Precipitation Outlook (L3MPO) NWS Climate Services Will be Precipitation

For Example: Pacific Islands – Sea-level forecasts Pacific Islands – Sea-level forecasts Florida – Forecasts for “storminess” or the number of storms expected to occur during the dry season Florida – Forecasts for “storminess” or the number of storms expected to occur during the dry season Baltimore, Maryland – Forecast for the likelihood of a major winter snow event Baltimore, Maryland – Forecast for the likelihood of a major winter snow event NWS Climate Services 3-Month Outlook of Local El Niño/La Niña Impacts (3MOLEI) El Niño/La Niña Outlooks based on local El Niño/La Niña signal

Summary There are long-term trends in the mean temperature and precipitation climates of North AmericaThere are long-term trends in the mean temperature and precipitation climates of North America Current models cannot be used to extrapolate those trendsCurrent models cannot be used to extrapolate those trends NOAA/NWS local forecast products provide services to the publicNOAA/NWS local forecast products provide services to the public Contact local forecast offices for more information Contact local forecast offices for more information

Background Slides

a b c Precipitation OND DJF AMJ

a b d Temperature MAM MJJ SON

Climate Forecast Skill

Product Development CD data Station data Regression Analysis Trend Significance Station Forecast Solution Verification filter CPC CD forecast Mean and St. Dev. No Significant? Compute Statistics and Regression Coefficients Intercept Adjustment Yes Skillful? Forecast data Distribution and Display Yes Climatology Data No y = mx + b (where m = slope and b = y-intercept) Graph Courtesy of Nicole Kempf y = mx + b (where m = slope and b = y-intercept)

Product Development CD data Station data Regression Analysis Trend Significance Station Forecast Solution Verification filter CPC CD forecast Mean and St. Dev. No Significant? Compute Statistics and Regression Coefficients Intercept Adjustment Yes Skillful? Forecast data Distribution and Display Yes Climatology Data No

Product Development y = mx + b (where m = slope and b = y-intercept) Graph Courtesy of Nicole Kempf

Product Development y = mx + b (where m = slope and b = y-intercept)