...forecast time series

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Use this page when you predict future values of something measured over time: sales per store, energy load, web traffic, river levels. Forecasting is regression with a time order, so the rules for testing are different (never shuffle time).

Start here

First, always: build a seasonal-naive baseline (next Monday = last Monday). Every model must beat it.

  • How many series, and how much history?
    • One or a few series with clear trend/seasonality → statistical models: exponential smoothing (ETS) and ARIMA (e.g., the statsforecast library); in a spreadsheet, Excel - Forecasting (FORECAST.ETS). Business data with holidays → Prophet
    • Many related series (thousands of products or stores) → one global model trained across all series: LightGBM with lag and calendar features, or deep models (N-BEATS/N-HiTS, Temporal Fusion Transformer, PatchTST)
    • Short history, new products, or you need a strong baseline today → time-series foundation models, zero-shot: Chronos-2 (Amazon), TimesFM (Google), Moirai (Salesforce), TimeGPT (Nixtla, as an API), Toto (Datadog, for observability metrics). Fine-tune if you have data.
  • Do outside drivers matter (price, promotions, weather, holidays)?
    • Yes → models that take covariates: gradient boosting with features, Temporal Fusion Transformer, Chronos-2
  • Do decisions need a range (stock levels, staffing, risk)?
    • Yes → probabilistic forecasts: quantiles from Chronos-style models, DeepAR, or quantile gradient boosting; or conformal intervals
  • Is it a physical system (weather, rivers, power grids)?
    • Yes → specialized physical or hybrid AI models (e.g., GraphCast for weather, flood models), not generic sales forecasters
  • Want to flag unusual values rather than predict them? → ...find outliers
  • Will the forecast drive an order, schedule or price? → forecast, then optimize: ...optimize decisions

Quick picks

Situation Try first Then compare
One series, clear seasonality ETS / ARIMA Prophet, a foundation model zero-shot
Thousands of related series Global LightGBM with lags and calendar features N-HiTS, TFT, Chronos-2 / TimesFM
Little history or cold start Chronos-2 or TimesFM zero-shot Hierarchical / grouped statistical models
Strong external drivers Gradient boosting with covariates TFT, Chronos-2 with covariates
Need intervals for decisions Quantile forecasts Conformal prediction around your best model
Spreadsheet users Excel FORECAST.ETS Prophet

Real-world examples

  • Retail demand (M5 competition) — forecasting Walmart unit sales across 42,840 hierarchical series; most top entries used LightGBM global models, and simple statistical methods remained hard-to-beat benchmarks. M5 Forecasting - Accuracy | Kaggle
  • Flood warnings — Google's AI river-flood forecasts give up to 7 days of warning in more than 100 countries, covering about 700 million people. Flood Forecasting | Google Research
  • Weather — DeepMind's GraphCast (a graph neural network) produces 10-day global forecasts in under a minute and beat the leading operational system (ECMWF HRES) on 90% of 1,380 test targets. Learning skillful medium-range global weather forecasting | Science
  • Cautionary tale — Zillow closed its home-buying business in 2021 after its price forecasts failed in a fast-moving market. See ...predict values.

What's new

  • Foundation models turn forecasting into model selection instead of model training. On the public GIFT-Eval benchmark, Chronos-2 reported better accuracy than earlier leaders such as TimesFM-2.5 and TiRex, and it supports covariates and multiple related series. Chronos-2: From Univariate to Universal Forecasting | arXiv
  • Read leaderboards carefully: some models were pretrained on data overlapping benchmark training sets, so test on your own history.

Watch out

  • Leakage: features that use future information (e.g., the month's final total) inflate test scores.
  • Wrong validation: use rolling-origin backtests (train on the past, test on the next window, repeat), not random splits.
  • Regime changes (pandemics, price shocks) break history; add judgment and scenario planning.

Measure success

MASE (vs. naive), WAPE or sMAPE (relative error), quantile loss or CRPS (for ranges), bias (systematic over/under-forecasting), all averaged over several backtest windows. More: ...evaluate and trust AI

Learn more


Where next? ◀ Predict & analyze · ...predict values · ...find outliers · ...optimize decisions · ▶ ...evaluate and trust AI