Keep usable surface observations with explicit times, units, missing values and precipitation intervals, then review actual changes.
Identify the station, instrument exposure and sampling interval. Use explicit UTC timestamps in the calculation record while preserving the original reporting time zone in notes. Define which readings are instantaneous, averages, gusts or accumulations. Do not combine a daily maximum with a spot temperature as though they were simultaneous.
Enter temperature, relative humidity, actual station pressure and wind on their documented bases. Use M for missing values and a true numeric zero only for a known zero. Keep instrument flags and unusual exposure conditions visible. Calm wind has no meaningful direction, so do not treat its zero-degree code as a northerly wind.
Use simultaneous temperature and humidity when checking saturation calculations. Below freezing, match the instrument humidity reference and distinguish a liquid-water dew point from a frost point. A thermodynamic wet bulb needs station pressure and the bulb phase. If using optical transmission, record the baseline and calibration; contrast range is not runway visual range.
Record the interval start and end, water-equivalent depth and gauge reading method. Use T for a trace and M when the amount is unknown. When reading a cumulative counter, form interval increments with documented reset handling before entering them; summing repeated cumulative totals would double-count rainfall.
Look at the actual observation sequence and the context of fronts, sensor exposure or maintenance. Calculate a three-hour pressure difference only from two readings exactly three hours apart. Do not infer an official pressure-tendency code from two values or turn an irregularly sampled mean into a daily mean.
Review flagged readings without deleting the raw data. Save the observation case with station and measurement notes, and export a portable copy. For climate work, obtain actual daily extrema and complete daily accumulations; for forecast verification, pair the observed quantity with the same valid time, height and interval.
Summarize actual timestamped readings and retain source and quality notes. · Reject overlapping depth intervals and retain trace counts separately. · Find exact three-hour station-pressure pairs and report sampled extrema and means.
Calculate a phase-documented dew or frost point and vapor pressure.
Solve a station-pressure wet or ice bulb, resolving a near-freezing phase ambiguity.
Calculate the 5% meteorological optical range from appropriate optical inputs.
Convert a collected liquid volume to equivalent depth using the receiving area.
Integrate interval-mean rates only when they represent each full time interval.
Convert an observed mean wind to the documented whole-knot Beaufort lookup convention.
Inspect daily coverage before treating a subtotal as a period total.
Verify forecasts only against compatible matched observations.
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Instrument exposure and reporting practice affect how readings can be compared.
Psychrometric saturation uses a specified ice/water reference; subzero frost point and liquid-water dew point are different quantities.
The optical-range definition uses a 5% transmission threshold under its stated conditions; night-light visibility and RVR require other treatment.
Record a gap explicitly instead of carrying forward the last value or entering zero rainfall.
Record the actual cloud observation and the coding scheme used; do not invent a METAR category from an informal fraction.