Where does this forecast come from Department of
- Slides: 26
Where does this forecast come from ? - Department of Commerce - NOAA - NWS - Portland Forecast Office + - Climate Prediction Center
What did we say last year?
Last year’s ENSO Model Predictions
Last year’s Summary • ‘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!
2011 -2012 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)
Climate Prediction Center CPC • Seasonal Forecasts are based largely on: – 10 year trends vs the 30 year average Average Temps for Downtown Portland Dec/Jan/Feb 1980 -2008 3 month average temp (deg F) 46 45 44 43 42 3 - Month Avg 5 year average 41 40 39 38 37 1980 1985 1990 1995 2000 2005
Climate Prediction Center CPC • Seasonal Forecasts are based largely on: – 10 year trends vs the 30 year averages – ENSO (El Niño / La Niña)
El Niño vs. La Niña • El Niño • Above normal sea surface temperatures in equatorial Pacific Ocean • La Niña • Below 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 Oceanic Nino Index Back-to-Back La. Nina’s are not uncommon El Niño Neutral La Niña
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
CPC’s Winter Outlook December 2011 – February 2012 Temperature Precipitation 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) ENSO-based Average Monthly Precipitation PDX 1950 -2010 8 Precipitation (inches) 7 6 5 Average Pcpn 1950 -2010 El Nino Avg Pcpn La Nina Avg Pcpn ENSO Neutral Avg Pcpn 2 nd La Nina Avg Pcpn 4 3 2 1 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
If it’s going to rain… When might it fall? (take with a grain of salt) ENSO-based Average Monthly Precipitation Government Camp 1953 -2009 18 16 Precipitation (inches) 14 12 Average Pcpn 1950 -2009 El Nino Avg Pcpn La Nina Avg Pcpn ENSO Neutral Avg Pcpn 2 nd La Nina Avg Pcpn 10 8 6 4 2 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Now the real question…what about snow?
Portland Airport Area Snow Data since 1940 La Niña years Average ~4. 5 inches / year
Snow Signals Cascades Lowlands
Just for fun…
18 69 18 70 73 18 -4 77 18 -8 81 18 -2 8 18 5 -6 89 -9 18 0 93 18 -4 97 190 8 119 2 0 119 5 -6 9009 9 --1 11991 100 13 119 3 --44 9117 119 7 --88 9221 119 1 --22 9225 11992 5 --66 299119 -3300 9333 3 -4 11993 -4 37 119 7 --88 9441 119 1 --22 9445 11994 5 --66 499 -5 - 0 11995350 53 -4 119 -4 957 1957 --88 1961 1 61 -2 19965 -2 1 6 199695 -66 6 199 -7700 1973 --44 1977 --88 1981 1 81 -2 19985 -2 19 85 -6 1989 -6 8 199 -990 1993 0 1 93 -4 19997 -4 2 97 -8 20001 -8 2001 --2 2005 2 05 -6 -6 Historic seasonal snowfall (inches) Portland 1871 -72 to 2008 -09 PDX Airport La. Downtown Nina Poly. (Downtown) La Nina * La Niña identified by the Coupled ENSO Index (Gergis and Fowler, 2005) 70 60 50 40 30 20 10 0
Snowfall Averages (inches) Downtown Portland 1871 -72 to 2008 -09 14. 0 12. 0 10. 0 Downtown Portland Average DJF Snowfall 1871 -72 to 2008 -09 8. 0 El Nino Avg DJF Snowfalll La Nina Avg DJF Snowfall 6. 0 ENSO Neutral Avg DJF Snowfall 4. 0 2. 0 0. 0
In Summary • ‘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!