Seasonal Forecasts

The 2-meter temperature anomaly forecasts averaged over three-month periods from November 2010 to June 2011 from NCEP’s Coupled Forecast System (CFS) model are shown below (additional fields including SST and wind anomalies are available here).

The most striking features are the strong negative anomalies over Alaska during the coming winter and early spring (a result of higher than normal pressures over the Gulf of Alaska, an atmospheric response to the La Nina in the tropical Pacific, and associated northerly winds over that state) and the strong positive anomalies over north-eastern Canada (associated with anomalous southerly winds forecasted for the western Atlantic). The cooler-than-normal temperatures over the central and eastern equatorial Pacific are associated with the La Nina that is expected to persist until at least late spring, although with weaker amplitudes later in the period. For Europe the CFS is forecasting temperatures slightly below average earlier in the period (in particular over eastern Europe) but close to average by late winter and early spring. As far as rainfall is concerned, the coming winter is expected to be drier than normal in particular over western and north-western Europe as can be seen here.

The ECMWF’s seasonal forecasts will be now discussed. Shown on the link below are the ensemble mean 2-meter temperature anomalies on the left and the corresponding MSLP anomalies on the right. The fields are averaged over three-month periods from October 2010 to March 2011. Shaded areas are significant at 10% level and solid contours at 1% level.

(file:///////home/swr07rmf/ECMWF_seasonal_forecast_sept10.jpg)

The biggest difference between these and NCEP’s forecasts with respect to the surface temperture is over north-eastern Asia where the former expects temperatures to be above average (with departures in excess of 2C in some regions) while the latter is forecasting temperatures close to or slightly below average. The signal over Europe is weak but there is a hint of cooler than normal temperatures in particular over south-eastern Europe.

Finally the seasonal forecasts by the Japanese model are shown. The plots below were taken from this website. The figures on the left show the 2-meter temperature anomalies and the ones on the right the precipitation anomalies averaged over DJF 2010/2011, MAM 20011 and JJA 2011. They suggest that in this coming winter temperatures are likely to be below the climatological average across western Europe with drier than normal weather conditions. The next Spring is also expected to be drier than normal but with temperatures slightly above the long-term average while the Summer will likely be drier than normal with temperatures slightly below average over north-western Europe and above average over south-eastern Europe.

It is important to stress that one cannot look only at three independent seasonal forecasts to make predictions. The forecast issued by the Beijing Climate Center (available here), for example, shows that it is more likely for temperatures to be above than below average over north-western Europe in the coming months.

Any comments/suggestions are more than welcome.

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2 Comments »

 
  • Clearly with predictions it is best to use as many independent forecasts as possible. The NWS/NCEP CFS and ECMWF forecasts appear to both identify colder than average conditions over Alaska, but they tend to disagree with the European weather. The ECMWF output does not report any signal for much of Europe, so there is neither an indication of above or below average temperature.

    If it helps any, my software that includes the monthly average jet-stream positions and the position of an Atlantic ocean blocking predicts winter temperatures close to the 1971-2000 average (+0.4C higher than 1961-1990). The colder conditions are predicted over the north, Scotland and particularly south-east England. Precipitation is anticipated to be slightly above average. That would imply a snowy winter.

    Of-course these forecasts are only in the trial stages. I would always recommend that customers obtain a selection of forecasts, rather than relying on the results of just one. I’ll be looking into developing further micro-models capable of running on desktop computers, to make predictions of the weather months ahead.

    • Ricardo says:

      Chris, I agree with you, one should look at as many forecasts as possible but I only found these two on the web. More recently I came across the Beijing Climate Center seasonal forecasts (available here). The signal over north-western Europe is weak although temperatures are more likely to be above average than below average over the UK in the coming months.

 

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