Frost Dates for 166 Canadian Towns

Yes — this page lists average last spring frost, average first fall frost and frost-free season length for 166 smaller towns across 10 provinces, in addition to the major cities covered elsewhere on the site. Every figure comes from Environment and Climate Change Canada's 1981-2010 Canadian Climate Normals, and each town names the specific weather station that recorded it along with that station's Climate ID, so you can verify any number directly at climate.weather.gc.ca. 56 towns of 166 come from 1991-2020 instead: those stations publish no frost section in 1981-2010 at all. The Period column marks each of them.

Because none is published for them. Plant hardiness zones in Canada come from Natural Resources Canada, and NRCan publishes zones for the country as a mapped surface rather than as a value for every town. Working one out ourselves would be original research that a reader could easily mistake for the official figure, so we do not do it. The frost dates here are measured values; a zone would be a guess, and the two do not belong in the same table. For a zone, check the NRCan plant hardiness map directly.

It matters a great deal, and it is the reason every row here names one. Many Canadian climate stations sit at airports, which are typically open, flat, low-lying ground where cold air pools on a clear still night — so an airport frosts earlier in fall and later in spring than the town centre a few kilometres away. 49 of these 166 stations are airport or automatic stations. Treat the date as the honest reading it is, from that specific site, and expect a sheltered urban garden to run a few days milder.

They are ECCC's own rating of how complete the station's record was over the reference period, and they are shown rather than filtered out. An A means the station had a nearly complete record, and a D means it did not — the value is still ECCC's published figure, but it rests on fewer years of observation, so treat it as a good estimate rather than a precise one. 35 of the 166 towns here carry an A rating.

Because for almost every station the average frost dates only exist in the older period. ECCC published the 1991-2020 normals with a frost-probability table — the date by which frost has passed at 10%, 25%, 50%, 75% and 90% likelihood — but without the plain averages. The mean date of last spring frost is only published for 1981-2010, so that is what a page about average frost dates has to use for all but a handful of stations. It is not a universal rule, and this page names any station where it does not hold: a few stations publish averages in 1991-2020 and nothing at all in 1981-2010, and those are taken from the newer period instead. Our frost-risk dataset covers the probability distribution from the newer period separately.

Pick the nearest listed town or city with similar terrain. Within about 50 km on comparable ground, frost dates typically shift only three to five days, so a nearby reading is a good guide. Elevation and distance from a large body of water matter more than raw distance: a town 20 km inland from a lake can frost noticeably earlier than one on the shore, and a valley bottom frosts before the slope above it. Many Canadian towns simply have no weather station, and several that do have one publish no frost average, so there is nothing honest we can list for them.