winter outlook (2011-2012) winter weather forecast conference omsi / oregon chapter of the ams 29...

Where does this forecast come from ?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?What did we say last year?

Last year’s ENSO Model PredictionsLast year’s ENSO Model Predictions

• ‘La Nina’ conditions are occurring and expected to continue through the winter of 2010-2011

• 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 2010-2011

• 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 SummaryLast year’s Summary

2011-2012So what about this winter?

2011-2012So what about this winter?

And where is this forecast coming from?And where is this forecast coming from?

Climate Prediction CenterCPC

Climate Prediction CenterCPC

• 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 CenterCPC

Climate Prediction CenterCPC

• 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 CenterCPC

Climate Prediction CenterCPC

• 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 ENSO Trends since 1950

El Niño

La Niña

Neutral

Oceanic Nino Index

Back-to-Back LaNina’s are not uncommon

La-Nina Conditions & Weather PatternsLa-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 OutlookDecember 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 aboutsnow?

Now the real question…what aboutsnow?

Portland Airport Area Snow Datasince 1940

Portland Airport Area Snow Datasince 1940

Average ~4.5 inches / yearLa Niña years

Snow SignalsSnow Signals

Lowlands

Cascades

Just for fun…Just for fun…

Historic seasonal snowfall (inches) Portland 1871-72 to 2008-09

Historic seasonal snowfall (inches) Portland 1871-72 to 2008-09

* La Niña identified by the Coupled ENSO Index (Gergis and Fowler, 2005)

Snowfall Averages (inches)

Downtown Portland 1871-72 to 2008-09

Snowfall Averages (inches)

Downtown Portland 1871-72 to 2008-09

In SummaryIn 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 averageprecipitation

Temperature – odds favoring near normal or cooler than normalconditions

Mountain Snow - significantly increased odds of an aboveaverage snowpack

Expect another active weather pattern this coming winter!

Thanks!Thanks!