What Is a Record Tie and How Do We Count One?
A record tie happens when a new observation equals the standing record for that station, element and calendar window at the precision the value is recorded. It matches the record without beating it, so the record value stays the same and the tie is noted beside it.
Why ties happen
Weather values are not continuous numbers. A thermometer reading is recorded to a fixed step, in our source data a tenth of a degree Celsius, and in some countries whole degrees or whole degrees Fahrenheit converted later. Rainfall and snow are recorded to a tenth of a millimetre or to a fixed increment. When values are rounded to a step, there is a real chance that two days in different years land on the same number.
The chance grows with three things:
- Coarse recording. Whole-degree records tie far more often than tenth-of-a-degree records.
- Clustering near the extreme. Values do not spread evenly. Close to the highest ever recorded, the possible values are few, and the chance of repeating one is real.
- Long histories. More years means more chances for a later year to land on the old value.
Precipitation adds a special case. The lowest possible value is zero, so a “record low” rainfall is meaningless, and we only track the high side. Snow depth is similar.
How we count ties
We store every tie as its own entry, with a margin of zero and the date of the tied record beside the original. Ties show on the day page, the station page and the ledger with a label, so a reader never mistakes one for a new record. Three counting rules follow.
- A tie is not a beat. A tie does not lift the record value, and it does not reset the age of the record.
- A tie counts in the ledger. It appears in the day count as its own line, next to new records, so the totals say “set or tied”.
- A tie scores lower. The significance score multiplies a tie by 0.5, since the value did not go beyond what was known.
A later observation that beats a tied record becomes a new record, and its margin is measured against the shared value.
Why other tools differ
Some tools fold ties into the count of records without a separate label, and some drop them. Both choices are reasonable, and neither is wrong. The difference is one reason our totals can differ slightly from a national agency’s for the same day. We list every difference we can explain on the methodology page.
Ties also interact with revisions. A value that ties today can turn into a beat, or into nothing, if the original observation is corrected during the following weeks. For that reason, records from the last 60 days are labelled provisional, and changes to them go into the corrections log.
Ties and the ratio
Record highs and record lows are counted once each per observation, and a tie counts on the same side as the record it matches. This keeps the ratio of record highs to record lows even-handed: a tie of a high record adds to the highs, a tie of a low record adds to the lows. Because ties depend on recording precision, they are a small share of the total in the ledger, but they are not zero, and hiding them would understate how often the extremes recur.
Ties and long-standing records
A long-standing record that is tied is interesting. It says the old value is still the benchmark, and that a later year came as close as the instruments can tell. On the longevity page, a record that has been tied keeps its original date and its full age. The list of near misses is related: it shows recent values that came close to a record without reaching it, and how big the gap was.
How to read a tie on a page
Look for the label “tie” next to a record. Then read the date and value of the record it tied. If the entry also says provisional, treat both facts as open until the label disappears. A reader who wants the underlying numbers can follow the link from the record to the station page and see the full history.
A worked example
Suppose a station’s highest recorded maximum for 3 August is 36.4 C, set in 1971. In a later year the station reads 36.4 C on 3 August. The reading equals the record, so the ledger stores a tie with a margin of zero, the daily record stays at 36.4 C from 1971, and the tie is listed with its own date. If another year reads 36.7 C, that is a new record with a margin of 0.3 C over the shared value. The record that stood is then the one from that new year, and the older one, together with its tie, falls into the history.
For the general definitions, see what a weather record is. Ties also count toward events such as heat waves, where clusters of records matter more than any single one.