Build a consistent daily weather record, retain missing and trace values, and compare only compatible observations and reference normals.
Record the station, exposure, instrument history, daily reporting cutoff and time zone. Identify moves, replacements and observing-practice changes. Choose actual daily extrema and interval precipitation data rather than treating a few spot observations as a complete daily record.
Keep raw data and quality codes before any correction. Enter M for missing temperatures or precipitation, T for a trace and zero for a measured zero. Check that minimum does not exceed maximum and that dates are real, unique and inside the selected period. An unlisted date is also missing coverage.
Review sampled extrema, the mean of available daily min/max means and the known precipitation subtotal. Read the coverage counts before describing a monthly or seasonal result. Traces add an unknown small amount above the numeric subtotal, while missing days leave the total unresolved.
Record the temperature base and calculation method before accumulating degree days. The provided mode uses the uncapped daily min/max mean for heating and cooling degree days. Crop-specific growing-degree-day methods can use different bases and caps; do not relabel this calculation as a crop model.
Obtain documented normals for the appropriate station, variable, baseline years and daily basis. Compare only common dates and use the correct aggregation: mean for daily temperatures, sum for daily accumulations. A short observation record does not create a new normal; missing reference values must remain missing.
Save the source data, period, quality decisions and reference normal version. Keep a correction log instead of overwriting unexplained values. Describe incomplete coverage and station changes alongside any comparison. A departure from a normal in one short period is not evidence of a long-term local trend.
Validate daily date coverage, paired temperature availability and precipitation flags. · Calculate daily summaries without filling absent dates or trace rain with measured zero. · Compute HDD and CDD subtotals on days with both extrema and retain the chosen base. · Calculate matched-date anomalies while displaying both observed and normal common-sample summaries. · Save separate original and corrected summary cases with portable copies.
Review sensor comparisons and dated maintenance context when a series changes.
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NOAA provides station normals on documented baseline periods and variable definitions; normals and short-term summaries serve different purposes.
NCEI Climate Data Online provides historical observations and station-history context for careful comparisons.
A trace is not a quantified zero; retain its count and the source notation.
A missing hot day in one series can change a mean even when the other series is complete.