Seasonal Forecast for ONDJFM 2012/2013 precipitation over South East Asia (forecasts
from September)
Forecast spreadsheet: SEA_GL4_forecast.xls
The spreadsheet SEA_GL4_forecast.xls contains the ensemble hindcasts and forecasts of
precipitation (mm/day) for all months from October 2012 to March 2013 from GloSea4. Both
forecasts and hindcasts were initialised in September. The hindcasts can be found in the
worksheet named Region1_hcst. This sheet contains the full hindcast set relating to the
retrospective forecasts (hindcasts) for each month (189 realisations, with a value for each
month). This hindcast will be used to calibrate the forecast. The forecasts can be found in
worksheet Region1_fcst, this sheet contains the 42 member ensemble forecast for each
season.
Purpose:
- to create a probability forecast for the season and region of most interest to your
country.
- to make adjustments to the probabilities based on reliability diagrams;
Procedure:
1. Select the hindcast worksheet (Region1_hcst).
2. In the green cells under ‘Seasonal mean’ create a hindcast set for the season of interest to
your country. For example if you are interested in ONDJ then in cell I2 you should write
“=AVERAGE(B2:E2)”. Then copy this to the remaining hindcast realisations.
3. In cell L2 find the model’s climatological seasonal mean for your chosen season. You
will need the AVERAGE function
4. In cells L5 and L6 find the model’s tercile boundaries for your chosen season. You will
need to use the PERCENTILE function and column L of your worksheet.
5. Now select the forecast worksheet (Region1_fcst).
6. In the green cells under ‘Seasonal mean’ create a forecast ensemble for the season of
interest to your country. For example if you are interested in ONDJ then in cell I2 you
should write “=AVERAGE(B2:E2)”. Then copy this to the remaining forecast members.
7. Cells L7 and L8 should show the tercile boundaries for the model over your chosen
season (as calculated in step 4.). In cells N3 and L3 calculate the forecast probabilities (in
%) of the lower and upper terciles respectively. You will need to use the COUNTIF
function and to refer to the values in cells L7 and L8.
8. Calculate the probability forecast for the middle tercile as a residual of the other
probabilities from the other two categories.
9. A histogram will develop showing the forecast probabilities for your chosen season.
Q. Consider the probability forecasts for your season and region, using your local knowledge
of teleconnections can you think of a reason that the model may be issuing the signal that you
see? You may wish to refer to the El Nino Southern Oscillation (ENSO) forecasts on the Met
Office web pages (http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpcoutlooks/ ).
Q. Consider both of the reliability diagrams below in turn. Assume that they show the
reliability diagram for your chosen region and season. How would you adjust your forecast
probabilities based on each of them?
Q. If you have access to the internet compare your results with the forecasts on the Met
Office web pages (http://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpcoutlooks/). Do they look plausible?
a)
b)