The precipitation quantity behind Wet-Day Frequency
Wet-day frequency is a count proportion. Its meaning depends on the threshold, observation day, trace rule, and treatment of missing records.
Wet-Day Frequency begins with days meeting wet-day threshold, valid observed days. Label each entry as measured, corrected, assumed, forecast, or derived before treating the output as a precipitation record.
Trace and missing observations
A trace is observed precipitation below the reporting increment, whereas missing means no usable observation. Wet-Day Frequency should never treat those codes as interchangeable without a stated convention.
When missing Wet-Day Frequency inputs later become available, preserve the earlier flagged result and document the recomputation rather than silently filling the historical record.
Boundary and direction checks
Zero wet days gives 0%; wet days equal to valid days gives 100%; wet count cannot exceed the valid count.
For Wet-Day Frequency, change one input at a time and predict whether the result should rise, fall, or stay fixed. This catches reversed subtraction, percent-as-fraction errors, overlapping intervals, and misplaced unit conversions.
From Wet-Day Frequency, continue with the related Average Rainfall Intensity Calculator.
Limitations of the Wet-Day Frequency model
Frequency from short samples can be unstable and is not a forecast probability. Changes in gauges, reporting time, trace coding, and completeness can create artificial trends.
Wet-Day Frequency provides transparent arithmetic, not a weather forecast, flood warning, drainage design, drought declaration, emergency instruction, or authority to operate in hazardous conditions.
Measurement uncertainty and sensitivity
Vary the least certain Wet-Day Frequency input across a credible range while keeping other entries fixed. Report how much wet-day frequency moves and whether interpretation changes.
That range is a sensitivity test, not a confidence interval. It explores selected inputs but does not capture every sampling, exposure, interpolation, model, or representativeness uncertainty affecting Wet-Day Frequency.
Depth, rate, probability, and area are different
Precipitation depth describes a layer, intensity divides depth by time, probability describes uncertainty, and areal estimates add spatial assumptions. Wet-Day Frequency should retain the quantity named in its formula.
Do not convert a point-gauge Wet-Day Frequency value into watershed volume or runoff without a defensible area model, unit conversion, and hydrologic assumptions.
Creating an auditable Wet-Day Frequency record
Save raw observations, exclusions, corrections, conversions, formula version, unrounded output, final rounding, and data-source identifiers. A reviewer should reproduce Wet-Day Frequency without guessing event or trace rules.
If a source value or method changes, issue a dated revision and retain the earlier result. Distinguish a data correction from a new Wet-Day Frequency scenario.
Using the result downstream
Transfer wet-day frequency with its unit, accumulation period, location or area, and measurement status. Downstream work can fail quietly when a rate is used as depth or a percentage as a fraction.
One Wet-Day Frequency value summarizes one defined calculation. Trends need repeated comparable records plus documented methods for gaps, trace amounts, instrument changes, and evolving station exposure.
Working formula for Wet-Day Frequency
The page applies Wet-day frequency = wet days ÷ valid days × 100. It uses only the displayed entries, so the calculation can be reproduced without an account, hidden weather feed, or unstated coefficient.
Keep full numerical precision through Wet-Day Frequency, then round according to gauge resolution, source uncertainty, and the intended comparison rather than the number of digits available on screen.
From Wet-Day Frequency, continue with the related Annual Exceedance Probability Calculator.
Checked example and expected result
Twelve wet days among 30 valid observed days produce a wet-day frequency of exactly 40%.
Reset restores that Wet-Day Frequency example. Rework it independently before substituting station, radar-derived, gridded, climatological, or scenario values.
Collecting compatible inputs
Define the wet-day threshold, such as at least 1 mm, before counting. Use complete comparable daily records and keep missing days out of both categories unless a method states otherwise.
Record site or area, start and end time, time zone, gauge type, exposure, reporting interval, precipitation phase, corrections, and quality flags with every Wet-Day Frequency result.
Interpreting Wet-day frequency
Forty percent means four in ten included days met the threshold. It does not show rainfall totals, event duration, or whether wet days were consecutive.
Compare Wet-Day Frequency outputs only when accumulation window, units, spatial support, event definition, and missing-data rules align. A numerical match can conceal incompatible records.
Common precipitation data traps
Typical Wet-Day Frequency errors include mixed millimetres and inches, local-day boundaries, duplicated intervals, missing values entered as zero, uncorrected snowfall catch, and mismatched climate periods.
Reject impossible Wet-Day Frequency field combinations instead of forcing an answer. Domain checks cannot determine whether a plausible number represents the right storm, station, basin, or period. Preserve the original precipitation code and observation resolution so later reviewers can distinguish a genuine zero from rounding, a trace, or unavailable data.
Questions about this precipitation result
What does Wet-Day Frequency report?
Wet-Day Frequency reports wet-day frequency using the displayed precipitation inputs, unit, and formula.
Can forecast or scenario values be entered?
Yes. Label a Wet-Day Frequency output as a scenario and do not present it as a measured gauge or verified forecast product.
How can I verify Wet-Day Frequency?
Repeat Wet-day frequency = wet days ÷ valid days × 100 with the recorded inputs, then test the checked example and a meaningful boundary case.
Why could another precipitation source disagree?
Another Wet-Day Frequency source may use different intervals, gauges, corrections, spatial methods, thresholds, climatological periods, or rounding.