Where does this forecast come from ? - Department of Commerce - NOAA - NWS - Portland Forecast Office + - Climate Prediction Center
Winter Outlook (2011-2012) Winter Weather Forecast Conference OMSI / Oregon Chapter of the AMS 29 October 2011 Winter Weather Forecast Conference OMSI.
Dec 22, 2015
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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!
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