What this tool does
Review many network periods without allowing a missing gauge to become either dry weather or somebody else's spatial weight.
When to use it
After retaining original observations and confirming the record basis. Run this decision independently; the other rainfall tools answer different questions and are not required merely to obtain a number.
Calculation or decision method
With an established fixed network, a complete period's mean is the sum of station depth × station weight. Enter weights as percentages of the whole basin. Only a sub-tolerance rounding difference around100% is normalized.
If any station is missing, do not publish a full-basin mean. Instead retain the available spatial weight, missing station IDs and the known weighted contribution. Do not renormalize the remaining stations. If no station is observed, even the known contribution is not an observed 0.
Worked example
Weights A 20%, B 30%, C 50% and depths 10,20,30 give 23 mm. A complete0,0,0 period has an observed mean 0. With NA,5,NA only 30% of the basin weight is observed: known contribution1.5 mm, but no whole-basin mean. Renormalizing that single observation to 5 mm would hide missing coverage.
Assumptions
Weights come from a verified basin boundary and station geometry/approved spatial method. All observations refer to matched periods/durations. A station's physical representativeness cannot be established just because the entered percentages add to 100. Obtain revised weights for a changed network.
Input and precision rules
Plain decimal, nonnegative depths; blank or NA means missing. Supported nonzero numbers run from 1e-12 to 1e9 in the entered basis. Inputs use ordinary browser floating-point precision, not arbitrary-precision metrology. Reconcile unsupported missing codes, tip counts, timezones, intensity values and changing clocks before entry. A malformed row stops the run rather than disappearing.
Limitations
No Thiessen polygon generation, GIS, kriging, radar interpolation, station replacement, missing rainfall estimate, runoff conversion or forecast. Do not sum the complete-period means and label them a complete record when other supplied periods are missing. Very small missing weights still make a period incomplete even when a rounded percentage appears near100%.
Keep the review packet
Export all periods with their coverage states and retain the original station observations plus the external weight map. Resolve missing observations through an appropriate documented project method before using a complete-series model. The screen/print preview is limited to 100 rows; audit CSV downloads retain every computed row. Copy result includes the full entered CSV and configuration. Keep sensitive project data within your own handling procedures; the site does not upload it.
Sources
- NOAA NWS — Basic Hydrologic Concepts: mean areal precipitation
- NOAA NWS — Precipitation measurements and spatial methods