How we get the number

What you see on the home page

Each home-page label maps to a stored CPC product, in plain words:

• Status sentence (phase and strength): last final RONI season from the CPC store. Plain-language strength labels (weak / moderate / strong) follow the historical Halpert / climate.gov classes (published on peak ONI) as readable bands on the stored RONI value. CPC does not publish RONI strength labels; we do not invent a new gauge, and we do not silently blend ONI and RONI into one number.
• The number / micro line: the stored RONI value, agency, product, and when we last stored a successful fetch.
• Chart bars: official three-month RONI seasons from the same store. Warmer / cooler than average, not a weather forecast.
• Optional outline bar: CPC monthly Niño-3.4 anomaly, display-only, until the next official RONI season is published. It does not write the status sentence.
• Place watch lines: historical regional composites (“often wetter / often cooler”). Not live city weather.

Strength bands (plain language)

Historical Halpert / climate.gov strength classes for El Niño episodes were published using peak seasonal ONI:

• Weak: peak ONI ≥ 0.5°C and ≤ 0.9°C
• Moderate: peak ONI ≥ 1.0°C and ≤ 1.4°C
• Strong: peak ONI ≥ 1.5°C

On this site we apply those same plain-language cutoffs to the absolute value of the stored seasonal RONI (live homepage product) so “weak / moderate / strong” stays readable. That is a site convention for wording . not a claim that CPC labels RONI with Halpert classes, and not a swap of ONI for RONI in the homepage number.

Phase uses the usual ±0.5°C seasonal threshold on stored RONI. When |RONI| < 0.5 we show ENSO-neutral (store enum remains Neutral for logic/CSS).

Pipeline

1. Fetch the public CPC ASCII files (we cache; we do not hammer CPC).
2. Keep phase, strength, index, season, agency, product, source URL, and a timestamp from that successful fetch.
3. Render the home page and status strips from that kept snapshot only.
4. If fetch fails: keep the last good snapshot and show “update failed [time]”.
5. If there is no snapshot yet: show a skeleton. Never a fake-looking placeholder number.

What we never invent

• No LLM-generated Pacific index.
• No city weather, radar, hourly, or 10-day forecast.
• No fake meters (AQI, fire, flood, “warning theater”).
• No invented CPC numbers, Change-link weather hops, or live station feeds.

Update cadence

CPC publishes official RONI as overlapping three-month seasons. We refresh when a fetch against those public files succeeds. We do not invent a fixed CPC publish weekday.

“Updated” on this site means the time of our last successful refresh (Europe/Rome on the stamp), not a new forecast we issued. Between CPC publications the number on the page stays put.

Official three-month RONI can lag the latest finished calendar month; that is why the chart sometimes shows a monthly outline bar until the next official season appears.

Sources

Public products we already fetch or cite for the home number, chart, and historical place lines.

• NOAA CPC RONI ASCII: preferred monitoring index for the home number.
• NOAA CPC ONI ASCII: documented reference; not the preferred live product.
• CPC monthly Niño-3.4 (detrend.nino34): optional chart outline bar only (ANOM column).
• climate.gov: ENSO: public explainers for regional historical patterns.
• NOAA CPC ENSO Diagnostic Discussion: official CPC advisories (Watch / Advisory / Final), not a forecast from us.
• CPC: El Niño temperature & precipitation patterns: historical composites behind “often…” lines.
• CPC: Warm episode impacts: historical warm-episode impacts used in the regional atlas.
• climate.gov: United States El Niño Impacts: Halpert historical classes (peak ONI) and U.S. patterns.

Recent stored seasons

Store series only: the same bars the home chart uses. Not a prediction.

Chart update failed

NOAA CPC