Subseasonal forecasting Sources of predictability Simon Mason simoniri
Sub-seasonal forecasting: Sources of predictability Simon Mason simon@iri. columbia. edu Teddy Allen tallen@iri. columbia. edu Ángel Muñoz agmunoz@iri. columbia. edu Cari. COF 2018 Wet/Hurricane Season – Seasonal Forecast Training Workshop Christ Church, Barbados, 22 – 23 May 2018
Forecast skill 2 Cari. COF 2018 Wet Hurricane Season Training Workshop
Definitions WMO Definitions of Meteorological Forecasting Ranges Nowcasting 0 – 2 hours Very short-range weather forecasting < 12 hours Short-range weather forecasting 12 – 72 hours Medium-range weather forecast 72 – 240 hours Extended-range weather forecasting 10 – 30 days Long-range forecasting Monthly outlook 3 -month or 90 -day outlook Seasonal outlook 30 days – 2 years 1 month (not necessarily the next one) 3 months (not necessarily the next three) 1 season (not necessarily the next one) Climate forecasting Inter-annual, decadal and multi-decadal Climate change scenarios > 2 years 3 Cari. COF 2018 Wet Hurricane Season Training Workshop
Weather prediction skill temperature 3 -day forecasts 4 Cari. COF 2018 Wet Hurricane Season Training Workshop
Weather prediction skill storm tracks 5 Cari. COF 2018 Wet Hurricane Season Training Workshop
Seasonal prediction skill temperature 6 Cari. COF 2018 Wet Hurricane Season Training Workshop
Seasonal prediction skill rainfall 7 Cari. COF 2018 Wet Hurricane Season Training Workshop
Forecast skill Source of skill: atmospheric initial conditions ECMWF forecast skill } Weekly average rainfall Anomaly correlation for Jun– Aug Source of skill: Madden-Julian Oscillation and Surface boundary conditions Li y Robertson, 2015 8 Cari. COF 2018 Wet Hurricane Season Training Workshop
Sources of predictability • Tropical-extratropical interactions: dispersion of Rossby waves by tropical tropospheric warming • Persistence of atmospheric regimes: e. g. , blocking • Persistence of oceanic conditions: in the tropics and the extratropics • Persistence of soil moisture anomalies: modifying the surfacelevel fluxes and the planetary boundary layer stability • Climatic modes at sub-seasonal scale, especially the Madden. Julian Oscillation (MJO), and other local regional modes, like SACZ and SIS • Interactions between sub-seasonal modes and modes at other timescales, like ENSO 9 Cari. COF 2018 Wet Hurricane Season Training Workshop
S 2 S Timescale: Sources of Predictability + Planetary oscillation (wave) at sub-seasonal scale. + Typical periodicity: 30 -60 days. + Always eastward propagating, amplifying or inhibiting rainfall in an organized way. + 8 phases. + Atmospheric and oceanic components. 10 Cari. COF 2018 Wet Hurricane Season Training Workshop
14 Cari. COF 2018 Wet Hurricane Season Training Workshop
MJO and precipitation anomalies (Dec – Jan) 1 2 3 4 5 6 7 8 http: //datoteca. ole 2. org/maproom/Sala_de_Mapas/Sub. Estacional-Map-3/index. html 15 Cari. COF 2018 Wet Hurricane Season Training Workshop
MJO and precipitation anomalies (Sep – Oct) 1 2 3 4 5 6 7 8 16 Cari. COF 2018 Wet Hurricane Season Training Workshop
S 2 S Timescale: Sources of Predictability Muñoz, 2017 (NOAA’s ENSO blog) Muñoz et al. , 2015 17 Cari. COF 2018 Wet Hurricane Season Training Workshop
Conclusions • Sub-seasonal timescales lie between weather (prediction from initial conditions) and seasonal (prediction from boundary conditions) timescales • Some predictability may be provided by both sources • In the tropics, the main source of sub-seasonal predictability is the Madden-Julian Oscillation (MJO). • The MJO is most pronounced in the Caribbean in the winter. 18 Cari. COF 2018 Wet Hurricane Season Training Workshop
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