NWS Data Sources Explained
The National Weather Service delivers temperature data through multiple formats with very different precision levels. Knowing which is which matters for trading.
Data Precision Hierarchy
NWS temperature data comes in 5 tiers, from least to most precise. For market trading, only the bottom tier (CLI) is what ultimately determines settlement:
Most frequent but least precise. Subject to the full F→C→round→F rounding pipeline. Good for tracking trends, unreliable for exact settlement values.
Official hourly observations with Celsius values rounded to one decimal place. Less rounding ambiguity than 5-minute data.
Special observations triggered by significant weather changes (e.g., thunderstorms, rapid temp shifts). Contain exact temperature readings without standard rounding.
Intra-day summary reports with very high precision. Published during the day, providing early looks at daily extremes.
The gold standard. Official highs, lows, and averages calculated from raw sensor data without additional rounding layers. Undergoes NWS review. This is what markets settle on.
One-Minute Observations (OMO)
ASOS stations continuously capture minute-by-minute temperature data. These One-Minute Observations exist but are not publicly displayed on the standard NWS timeseries pages.
OMO data is used internally to calculate 6-hour and 24-hour maximums and minimums, which feed into the official daily summary. So while you can't see the one-minute readings, they influence the final CLI values that settle markets.
Preliminary vs Final Data
Every temperature observation you see in real-time is preliminary. It has not undergone NWS quality control review. This means:
- •Faulty sensor readings might be adjusted or removed in the final record
- •Temporary sensor malfunctions during the day could produce outlier readings
- •The NWS may apply corrections before publishing the official CLI report
The CLI report — typically published the following morning — is the first dataset that has undergone NWS review and represents the official record.
What minuteTemp Shows
minuteTemp displays NWS station observations polled every 60 seconds. When a station goes quiet (which can happen for up to 30 minutes), we use LOCF (Last Observation Carried Forward) — the most recent reading continues to display until a new one arrives.
On the chart, observed readings include a precision envelope: a red line for the estimated maximum and a blue line for the estimated minimum. Hover tooltips showActual, Min, and Max values directly.
External API and WebSocket observation payloads include these bounds astemp_min_fandtemp_max_fso downstream systems can use the same uncertainty model.
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