1. Zimbabwe 2017/18 Seasonal update
Meteorological Services Department Of Zimbabwe
20 December 2017

2. OCTOBER-NOVEMBER-DECEMBER (OND) 2017
Definitions
Above normal: rainfall in excess of 125 % of the average
Normal: Between 75% and 125 % of the average
Below: rainfall below 75% of the average
LONG TERM AVERAGE: averaged for period 1981 to 2010
OND OUTLOOK
A 35
N 40
B 25
A 25
N 40
B 35

3. Long-term Seasonal onset
Definitions: start of season is any day after the 1st of October that a place receives 20 mm or more in 1 or
two days provided there is no dry spell of 10 or more in the next 20 days.
Dry day: is a day which receives less than 0.85mm
Rainday: is a day which receives 0.85mm or more rainfall
Wet day: is a day with 10mm or more
Mean onset (SOS) of the rainfall season (period 1981 to 2016)
Standard error(SE) of SOS mean: SE ± mean
onset gives the window for onset dates

4. Start anomaly for 2017-18 season: current SOS
Seasonal onset
Definitions: start of season is any day after the 1st of October that a place receives 20 mm or more in 1 or
two days provided there is no dry spell of 10 or more in the next 20 days.
Dry day: is a day which receives less than 0.85mm
Rainday: is a day which receives 0.85mm or more rainfall
Wet day: is a day with 10mm or more
Start anomaly for season: current SOS
minus long-term mean onset
Start of season (SOS) for current season ( ) according to
the above definition of start of season

5. Raindays and wet days for 2017-2018
Definitions: start of season is any day after the 1st of October that a place receives 20 mm or more in 1 or
two days provided there is no dry spell of 10 or more in the next 20 days.
Dry day: is a day which receives less than 0.85mm
Rainday: is a day which receives 0.85mm or more rainfall
Wet day: is a day with 10mm or more
Wet days anomaly for season: current number of wet days minus mean number of wet days to date; ref to definition above
Raindays anomaly ( ): current number of raindays
minus long-term mean number of raindays to date

6. Percentage of normal rainfall as from
ACCUMULATED AND PERCENTAGE OF NORMAL FOR RAINFALL SEASON
Definitions
Above normal: rainfall in excess of 125 % of the average
Normal: Between 75% and 125 % of the average
Below: rainfall below 75% of the average
Percentage of normal rainfall as from
1 October 2017 to 13 December 2017).
Accumulated Rainfall in mm as from
1 October 2017 to 13 December 2017.)

7. DATES WHEN WATER BALANCE GOT TO ZERO IN THE CURRENT
DATES WHEN WATER BALANCE GOT TO ZERO IN THE CURRENT ( ) RAINFALL SEASON

8. 2017-2018 SEASONAL OUTLOOK UPDATE FOR JANUARY-FEBRUARY-MARCH
Definitions
Above normal: rainfall in excess of 125 % of the average
Normal: Between 75% and 125 % of the average
Below: rainfall below 75% of the average
LONG TERM AVERAGE
OUTLOOK