Seasonal Rainfall Outlook Platform
Historical skill · Apr 2026 · FMAM 2026 — February initialization · FMAM rainfall contribution domain

Historical skill · Apr 2026

How forecasts made with the same method scored in past years against climatology (the observed frequency of each tercile in the training years, about one-third each). The main number is the cross-validated 1993–2016 score: each year is forecast with parameters fitted without that year. Later years are exploratory: they were seen while the method was chosen.

Takeaway — Apr 2026

Historical skill is uncertain: cross-validated 1993–2016 RPSS is +0.011, and its interval (−0.032 to +0.048) includes no improvement over climatology. The exploratory 2017–2025 result (+0.015) is encouraging but those years were inspected during method selection. The 2026 verification (−0.187) is one season and does not override the historical uncertainty.

Stronger historical evidence (interval above zero): Feb +0.137.

FMAM 2026 (February initialization), FMAM rainfall contribution domain: probability skill (RPSS) of the final method against climatology, with whole-year 95% intervals
TargetCross-validated 1993–2016 (main)In wordsExploratory 2017–2025
Apr+0.011 (−0.032 to +0.048)Small estimated improvement; skill uncertain+0.015 (−0.009 to +0.042)
FMAM+0.017 (−0.038 to +0.067)Small estimated improvement; skill uncertain+0.061 (+0.029 to +0.095)
Feb+0.137 (+0.050 to +0.234)Moderate improvement over climatology (interval above zero)+0.049 (−0.017 to +0.128)
Mar+0.011 (−0.020 to +0.042)Small estimated improvement; skill uncertain+0.041 (+0.007 to +0.080)
May+0.007 (−0.051 to +0.050)Small estimated improvement; skill uncertain+0.017 (−0.033 to +0.057)

RPSS +0.05 means a 5% lower ranked probability score than climatology. An interval that includes zero means the gain is not established.

Technical detail: years better, p-values and blend weights
TargetYears better (cross-validated)p (one target / Holm)Years better (exploratory)Blend weight λ
FMAM15 of 240.276 / 1.0008 of 90.40
Feb16 of 240.002 / 0.0125 of 90.50
Mar15 of 240.251 / 1.0007 of 90.73
Apr16 of 240.305 / 1.0005 of 90.58
May17 of 240.434 / 1.0008 of 90.55

Each interval and one-target p-value describes that target alone. Because 5 targets are examined, the Holm-adjusted p is the stricter test: Feb remains significant after adjustment. λ is the weight given to climatology in the blend (higher = closer to climatology).

Historical verification explorer

The evidence behind the scores above, for Apr 2026 in this area. Choose the evaluation period; all diagnostics use the blended probabilities against climatology.

Evaluation
Cross-validated (nested leave-one-year-out), 1993–2016
Benchmark
Climatology: observed tercile frequencies of the training years (about one-third each)
Area
FMAM rainfall contribution domain; probabilities on 100% of it on average
Sample
24 years, 26,880 cell-years. Cells within a year are spatially correlated, so the independent sample is closer to one value per year.

Performance by year

Probability skill (RPSS) of each year; better than climatology in 15 of 24 years. Weakest years: 2011 (−0.292), 2006 (−0.127), 1998 (−0.105).

Better than climatologyWorse
−0.30−0.20−0.100.00+0.10+0.201993: RPSS +0.073 (forecast RPS 0.442, climatology 0.477; 1120 cells)19931994: RPSS −0.021 (forecast RPS 0.450, climatology 0.440; 1120 cells)1995: RPSS −0.086 (forecast RPS 0.525, climatology 0.483; 1120 cells)1996: RPSS −0.003 (forecast RPS 0.406, climatology 0.405; 1120 cells)1997: RPSS +0.153 (forecast RPS 0.422, climatology 0.499; 1120 cells)199719971998: RPSS −0.105 (forecast RPS 0.489, climatology 0.443; 1120 cells)1999: RPSS +0.061 (forecast RPS 0.456, climatology 0.485; 1120 cells)2000: RPSS +0.118 (forecast RPS 0.397, climatology 0.450; 1120 cells)2001: RPSS +0.093 (forecast RPS 0.412, climatology 0.454; 1120 cells)20012002: RPSS +0.044 (forecast RPS 0.407, climatology 0.426; 1120 cells)2003: RPSS −0.070 (forecast RPS 0.480, climatology 0.448; 1120 cells)2004: RPSS +0.086 (forecast RPS 0.396, climatology 0.433; 1120 cells)2005: RPSS −0.027 (forecast RPS 0.398, climatology 0.388; 1120 cells)20052006: RPSS −0.127 (forecast RPS 0.511, climatology 0.453; 1120 cells)2007: RPSS +0.025 (forecast RPS 0.377, climatology 0.386; 1120 cells)2008: RPSS +0.085 (forecast RPS 0.438, climatology 0.478; 1120 cells)2009: RPSS +0.110 (forecast RPS 0.401, climatology 0.450; 1120 cells)20092010: RPSS +0.018 (forecast RPS 0.432, climatology 0.440; 1120 cells)2011: RPSS −0.292 (forecast RPS 0.661, climatology 0.512; 1120 cells)20112012: RPSS +0.018 (forecast RPS 0.399, climatology 0.406; 1120 cells)2013: RPSS +0.038 (forecast RPS 0.462, climatology 0.480; 1120 cells)20132014: RPSS +0.014 (forecast RPS 0.485, climatology 0.492; 1120 cells)2015: RPSS 0.000 (forecast RPS 0.508, climatology 0.508; 1120 cells)2016: RPSS +0.090 (forecast RPS 0.403, climatology 0.443; 1120 cells)

Reliability

below normalnear normalabove normal
0.00.00.20.20.40.40.60.60.80.81.01.0below normal: forecast 19%, observed 43% (132 cell-years, too few to judge)below normal: forecast 27%, observed 32% (5542 cell-years)below normal: forecast 35%, observed 33% (15680 cell-years)below normal: forecast 43%, observed 44% (5433 cell-years)below normal: forecast 51%, observed 30% (93 cell-years, too few to judge)near normal: forecast 19%, observed 17% (230 cell-years)near normal: forecast 27%, observed 25% (11879 cell-years)near normal: forecast 34%, observed 34% (13198 cell-years)near normal: forecast 43%, observed 41% (1460 cell-years)near normal: forecast 54%, observed 32% (113 cell-years, too few to judge)above normal: forecast 20%, observed 5% (20 cell-years, too few to judge)above normal: forecast 27%, observed 25% (6782 cell-years)above normal: forecast 34%, observed 37% (15568 cell-years)above normal: forecast 43%, observed 42% (4286 cell-years)above normal: forecast 53%, observed 20% (221 cell-years)above normal: forecast 62%, observed 33% (3 cell-years, too few to judge)Forecast probability

Points on the dashed diagonal are reliable: events forecast with probability p happen p of the time. Points flatter than the diagonal mean over-confident probabilities. Open points have fewer than 134 cell-years (0.5% of the sample, at least 50) and are not joined. Hover a point for its count.

Reliability table (forecast bins, observed frequency, counts)
CategoryBinMean forecastObserved frequencyCell-years
below normal10%–20%19%43%132
below normal20%–30%27%32%5,542
below normal30%–40%35%33%15,680
below normal40%–50%43%44%5,433
below normal50%–60%51%30%93
near normal10%–20%19%17%230
near normal20%–30%27%25%11,879
near normal30%–40%34%34%13,198
near normal40%–50%43%41%1,460
near normal50%–60%54%32%113
above normal10%–20%20%5%20
above normal20%–30%27%25%6,782
above normal30%–40%34%37%15,568
above normal40%–50%43%42%4,286
above normal50%–60%53%20%221
above normal60%–70%62%33%3

How strong are the signals?

Share of cell-years by the leading tercile probability.

weak (<40%)
57%
moderate (40–50%)
42%
strong (50–60%)
2%
very strong (≥60%)
0%
Category Brier scores (lower is better) and Brier skill against climatology
CategoryForecastClimatologyBrier skill
below normal0.22580.2267+0.004
near normal0.20890.2121+0.015
above normal0.22240.2266+0.019

Rainfall amounts

Historical rainfall-amount diagnostics (CRPS, CRPSS and amount errors) have not been generated for Apr 2026 in this area and period; this needs a separate cross-validated amount evaluation. Single-season amount scores are in the Verification section.

Historical performance by rainfall region

Probability skill by rainfall region (full regional matrix)
FMAM 2026: probability skill (RPSS) by rainfall region, cross-validated 1993–2016, with whole-year 95% intervals and years better than climatology
RegionFMAMFebMarAprMay
All Ethiopia+0.021 (−0.031 to +0.069) 15/24 yrs+0.126 (+0.043 to +0.217) 18/24 yrs+0.011 (−0.017 to +0.038) 15/24 yrs+0.009 (−0.034 to +0.044) 15/24 yrs+0.008 (−0.042 to +0.047) 16/24 yrs
R0 arid / marginal+0.023 (−0.072 to +0.103) 15/24 yrs+0.057 (−0.081 to +0.206) 13/24 yrs−0.005 (−0.058 to +0.044) 15/24 yrs−0.028 (−0.102 to +0.038) 13/24 yrs−0.015 (−0.079 to +0.040) 13/24 yrs
R1 western unimodal+0.019 (−0.035 to +0.067) 18/24 yrs+0.156 (+0.068 to +0.248) 18/24 yrs+0.009 (−0.018 to +0.034) 15/24 yrs+0.016 (−0.024 to +0.047) 17/24 yrs+0.009 (−0.033 to +0.046) 15/24 yrs
R2 Belg–Kiremt+0.037 (−0.050 to +0.108) 17/24 yrs+0.166 (+0.076 to +0.264) 20/24 yrs+0.023 (−0.017 to +0.058) 16/24 yrs−0.001 (−0.063 to +0.052) 14/24 yrs+0.009 (−0.051 to +0.059) 16/24 yrs
R3 Gu–Deyr+0.012 (−0.042 to +0.064) 15/24 yrs+0.082 (−0.006 to +0.180) 14/24 yrs+0.006 (−0.030 to +0.041) 14/24 yrs+0.017 (−0.034 to +0.064) 16/24 yrs+0.009 (−0.066 to +0.062) 19/24 yrs
FMAM rainfall contribution domain+0.017 (−0.038 to +0.067) 15/24 yrs+0.137 (+0.050 to +0.234) 16/24 yrs+0.011 (−0.020 to +0.042) 15/24 yrs+0.011 (−0.032 to +0.048) 16/24 yrs+0.007 (−0.051 to +0.050) 17/24 yrs
FMAM main-season rainfall domain (Belg / Gu / Ganna, >=40% of annual)+0.013 (−0.040 to +0.066) 16/24 yrs+0.080 (−0.005 to +0.176) 14/24 yrs+0.007 (−0.029 to +0.042) 15/24 yrs+0.013 (−0.041 to +0.060) 17/24 yrs+0.009 (−0.066 to +0.062) 18/24 yrs

Positive values mean lower RPS than climatology. Intervals resample whole years; regions are the fixed 1993–2025 rainfall regimes, and the last rows are this cycle's rainfall domains. Regional results are noisier than national ones.