SNOPAC: Western Seasonal Outlook (8 December 2011) Portland, OR By Jan Curtis

Nature of Weather Forecasting: The Inconvenient Truth Weather forecast skill improves 1 day every 10 years However, slight errors in initial conditions make a forecast beyond two weeks nearly impossible

Nature of Weather Forecasting Function of initial condition – Model physics – Ensemble’s mean best predictor QC / Data Access (Assimilation)

Ensemble (Spaghetti Western) Advantages : Compact presentation of information All ensemble members are shown We can get an idea of the probability distribution for the forecast for the contours we display. Disadvantages : Do not have a full picture of the forecast probability distribution Requires additional information for good interpretation of products  Can use spaghetti and ensemble mean and spread diagrams together (where largest spread indicated) to get a better picture of the ensemble forecast probability distribution Ref:

Observed & Ensemble Forecasts (previous 4 months) Ref: Always looking for shifts in the weather pattern & changes in forecast confidence Latest series of runs suggest major change possible during last week in December

Maps showing correlation during between the teleconnection index and monthly surface precipitation & temperature departures for the three months centered on the month of interest. For example, the January pattern shows the correlation between the January values of the teleconnection index and the monthly precipitation & temperature departures during December, January, and February. North Atlantic Oscillation (NAO): Positive Phase

Maps showing correlation during between the teleconnection index and monthly surface precipitation & temperature departures for the three months centered on the month of interest. For example, the January pattern shows the correlation between the January values of the teleconnection index and the monthly precipitation & temperature departures during December, January, and February. Pacific / North American Pattern (PNA): Positive Phase

Arctic Oscillation: All Phases (Precipitation) + N - The AO is a virtually meaningless index for the Pacific NW.AO

Arctic Oscillation: All Phases (Temperature) The following months had +AO December 2008, January 2007, December 1998, December 1992/January 1993, December 1990, February 1990, February/March 1989, December 1984, November 1978, December 1972/January 1973, January 1962, January 1957, and December Widespread snow and Arctic air in all of them. By contrast things haven't worked out well for the Pacific NW during periods of mega -AO lately. +AO means more Arctic air building in the Arctic, there will be plenty to tap into if the right pattern falls into place. + N -

Winter Patterns

Let’s see what pattern is occurring nowpattern

November 2011 Final drier cooler

Analogs

November 2011 Verification drier cooler

Corr= Dec 11 Run Daily CPC Forecast Analogs Verified well More confidence

Corr= Dec 11 Run Daily CPC Forecast Analogs Verified poorly Less confidence

Corr= Dec 11 Run Daily CPC Forecast Analogs But I have Less confidence Verified well

Corr= Dec 11 Run Daily CPC Forecast Analogs Less confidence Verified mixed

Corr= Dec 11 Run Daily CPC Forecast Analogs Less confidence Verified poor

Corr= Dec 11 Run Daily CPC Forecast Analogs Less confidence Verified poor consistent Ref:

December Verification (Thus Far) dry wet cool

Alaska (Anchorage) 2.55”

Alaska (Fairbanks) 0.13”

Alaska (Juneau) 13.75”

Alaska (Nome) 1.69”

Alaska surplus deficit Ref: Storm TracksStorm Tracks

Inconvenient Truths Similar analogs may have gotten there through different mechanisms – Climate Change is an unknown factor The PDO/ENSO (one entity) are the base state of the climate system – The Climate System is always attempting to restore energy balance (ATM has memory) ENSO is the best predictor but is still only 10% above random skill Alaska, the Northern Tier, and South Tier weather are counter-opposed Water Supply Forecasts are “only” as good as the Weather Forecast and availability of data Best long range forecast (>14 days) is persistence followed by climatology – Analogs (statistical based) and Dynamic (numerical) Model Forecasts are less reliable Ref:

The Forecast (10 Weeks into WY-12)

Forecast (repeat of )? X X = bad start X  

The Prediction Expect Colder West Late Runoff Below Possible