Winter Outlook ( ) Winter Weather Forecast Conference OMSI / Oregon Chapter of the AMS 29 October 2011 Winter Weather Forecast Conference OMSI / Oregon Chapter of the AMS 29 October 2011 David Elson Meteorologist National Weather Service Portland, OR

Where does this forecast come from ? - Department of Commerce - NOAA - NWS - Portland Forecast Office + - Climate Prediction Center - Department of Commerce - NOAA - NWS - Portland Forecast Office + - Climate Prediction Center

What did we say last year?

Last year’s ENSO Model Predictions

‘La Nina’ conditions are occurring and expected to continue through the winter of Can expect this Winter to be (on average): –Temperature – increased odds on cooler than normal conditions –Precipitation – increased odds on above average conditions –Mountain Snowpack – increased odds of an above average snowpack Expect an active winter weather pattern this coming winter in the Pacific Northwest! ‘La Nina’ conditions are occurring and expected to continue through the winter of Can expect this Winter to be (on average): –Temperature – increased odds on cooler than normal conditions –Precipitation – increased odds on above average conditions –Mountain Snowpack – increased odds of an above average snowpack Expect an active winter weather pattern this coming winter in the Pacific Northwest! Last year’s Summary

So what about this winter? And where is this forecast coming from?

Climate Prediction Center CPC Seasonal Forecasts are based largely on: –10 year trends vs the 30 year averages –ENSO (El Niño / La Niña) Seasonal Forecasts are based largely on: –10 year trends vs the 30 year averages –ENSO (El Niño / La Niña)

Climate Prediction Center CPC Seasonal Forecasts are based largely on: –10 year trends vs the 30 year average Seasonal Forecasts are based largely on: –10 year trends vs the 30 year average

Climate Prediction Center CPC Seasonal Forecasts are based largely on: –10 year trends vs the 30 year averages –ENSO (El Niño / La Niña) Seasonal Forecasts are based largely on: –10 year trends vs the 30 year averages –ENSO (El Niño / La Niña)

El Niño vs. La Niña La Niña Below normal sea surface temperatures in equatorial Pacific Ocean El Niño Above normal sea surface temperatures in equatorial Pacific Ocean Index values (ONI) represent temperatures in the Niño 3.4 region

La Niña - again La Niña conditions redeveloped in Aug 2011 Negative Sea surface temperature (SST) anomalies are strengthening in the eastern half of the Pacific Ocean

La Niña - again La Niña conditions are expected to gradually strengthen and persist into the winter months

ENSO Trends since 1950 El Niño La Niña Neutral Oceanic Nino Index Back-to-Back LaNina’s are not uncommon

La-Nina Conditions & Weather Patterns

La Niña tendencies December - February La Niña by itself favors: ~60% chance of precipitation above normal ~30% chance of precipitation near normal ~10% chance of precipitation below normal

La Niña tendencies December - February La Niña by itself favors: ~35-55% chance of temps averaging below normal ~35% chance of temps averaging near normal ~10-30% chance of temps averaging below normal

Temperature Precipitation CPC’s Winter Outlook December 2011 – February 2012 The seasonal outlooks combine the effects of long-term trends, soil moisture, and when appropriate, ENSO.

If it’s going to rain… When might it fall? (take with a grain of salt)

If it’s going to rain… When might it fall? (take with a grain of salt)

Now the real question…what about snow?

Portland Airport Area Snow Data since 1940 Average ~4.5 inches / year La Niña years

Snow Signals Lowlands Cascades

Just for fun…

Historic seasonal snowfall (inches) Portland to * La Niña identified by the Coupled ENSO Index (Gergis and Fowler, 2005)

Snowfall Averages (inches) Downtown Portland to Snowfall Averages (inches) Downtown Portland to

In Summary ‘La Nina’ conditions are occurring and expected to gradually strengthen and continue this winter This Winter we can expect (odds favoring): ‘La Nina’ conditions are occurring and expected to gradually strengthen and continue this winter This Winter we can expect (odds favoring): Precipitation – significantly increased odds on above average precipitation Temperature – odds favoring near normal or cooler than normal conditions Mountain Snow - significantly increased odds of an above average snowpack Expect another active weather pattern this coming winter!

Thanks!