First Frost Dates by City: the Data

First frost dates for the 100 largest US cities

The median first fall frost across the largest US cities is November 9. That is the middle of 82 cities whose reference weather station records a 32°F freeze in at least half of years, using the NOAA 1991-2020 US Climate Normals. The other 18 cities, all in AZ, CA, FL, HI, do not have a first frost in a typical year at all. Together the 100 cities hold about 64.5 million people (Census Vintage 2023 estimates).

This page lists, for each city, the date of the median first fall freeze, the date by which the first freeze arrives in one year out of ten, the median last spring freeze and the median freeze-free season. Every number comes from one of three public datasets, and the whole table is a CSV download you can reuse under CC BY 4.0.

Key findings

• 82 of 100 cities freeze in a typical year; 18 do not. The frost-free group ranges from 9 cities with a freeze in 1 percent of years or fewer (among them Los Angeles, San Diego, San Francisco, Miami and Honolulu) to Port St. Lucie at 48.5 percent. Phoenix Sky Harbor records a freeze in 17.5 percent of years. (n = 100)
• The earliest median first frost is Anchorage, Oct 1, followed by Colorado Springs (Oct 8), Denver (Oct 9), Aurora (Oct 9). The latest are Orlando (Jan 10), New Orleans (Dec 31), Riverside (Dec 30), Scottsdale (Dec 26). (n = 82)
• 26 of the 82 freezing cities (32 percent) reach their median first frost before November 1. By month: 26 in October, 36 in November, 19 in December and 1 in January.
• The 1-in-10 early first freeze is a median 14 days before the usual date. In the typical city, one year in ten freezes at least 14 days ahead of the median first frost; the widest gap is 30 days. In spring, the 1-in-10 late freeze lands a median 16 days after the median last frost. (n = 82)
• Same USDA zone, very different frost dates. Within zone 9b, median first freeze dates run from Dec 1 (Stockton) to Dec 31 (New Orleans), a 30-day spread across 11 cities. Zone 7a runs 28 days, from Spokane (Oct 12) to Boston (Nov 9).
• The median freeze-free season is 222 days. The median last spring frost is March 31. The shortest season is Anchorage at 147 days.

Why the zone is not your frost date

A USDA hardiness zone is built from one number: the average coldest night of the year. A first frost date is about timing, the first night each fall when the air at the station drops to 32°F. The two are related, because places with cold winters tend to cool off earlier, but they are not the same measurement, and the chart shows how loose the link is. Coastal and lakeside cities hold their warmth into late fall and get a late first frost for their zone. High, dry cities cool fast on clear nights and get an early one.

Zone 9b is the widest case in this set. Zone 6b is the tightest, 4 days across 8 cities. This site uses a representative frost window per zone on its zone pages; checked against these stations, that window lands within a week of the city's own median first frost for 44 of 82 cities and is more than two weeks off for 8. That is why the city frost date pages and the ZIP lookup use station dates, and why a gardener should too.

First frost by USDA zone

How to read the dates

The median first frost is a coin flip, not a deadline: in half of years the first 32°F night comes before it. If a crop would be lost to one light freeze, the 1-in-10 column is the safer planning date, because only one year in ten freezes earlier than that. The same logic runs in reverse in spring, where the "1-in-10 late" date is the one to wait for before setting out tomatoes and peppers. Our first frost guide covers what row cover, mulch and water buy you on either side of those dates, and the fall planting calendar counts sow-by dates back from them.

12 cities freeze in most years but not every year, from Riverside (57.5 percent of years) to Bakersfield (89.5 percent). For them the first frost date describes the years that freeze, and in a mild winter there is no first frost at all. Tender perennials there survive most winters and are lost in the occasional hard one.

Several cities share a station. Mesa, Chandler, Gilbert and Glendale all use Phoenix Sky Harbor, Aurora uses Denver International, and Fort Worth uses Dallas/Fort Worth International, so their rows are identical. Your own yard can differ from the station by a week or more: valley floors and open rural ground freeze earlier than airports, and dense city centers freeze later.

All 100 cities

Methodology

Cities. The 100 most populous places in the US Census Bureau's Vintage 2023 city and town population estimates (incorporated places plus Urban Honolulu), ranked by the July 1, 2023 estimate. Each city is located at its internal point from the Census 2020 place gazetteer, except San Francisco, whose gazetteer point is pulled offshore by the Farallon Islands and was replaced with City Hall.

Stations. For 30 cities we used the station the National Weather Service treats as the city's official climate record (usually the main airport). For the other 70 we used the nearest first-order (WBAN, "USW") station within 60 km that publishes 1991-2020 freeze normals. The median city-to-station distance is 11 km; the largest is Anchorage at 39.9 km. 88 distinct stations in all.

Frost dates. From the NOAA NCEI 1991-2020 annual and seasonal normals, 32°F threshold: the 50 percent probability dates of the last spring and first fall freeze, the 10 percent dates (a first freeze on or before that date in one year in ten; a last freeze on or after it in one year in ten), the 50 percent freeze-free season length, and the probability of a year having any 32°F night. Where that probability is under 50 percent we show no median dates, because NOAA's dates there describe only the minority of years that do freeze.

Zones. The USDA 2023 Plant Hardiness Zone Map half zone most common among ZIP code centroids within 10 km of the city point, from the same ZIP dataset that powers this site's lookup.

What was not measured. These are 32°F air-temperature freezes about 1.5 m above the ground at the station, not frost on plants: frost can form on leaves when the station reads a few degrees above freezing on a clear, still night. NOAA also publishes 28°F hard-freeze dates, which matter for hardy crops; they are not in this table. We did not measure soil temperature, microclimate, or elevation differences inside a city, and we did not test for trends within 1991-2020: the normals are 30-year probabilities, so a warming trend inside the period is averaged in, not shown. Stations change instruments and surroundings over three decades; NOAA's quality control handles some of that and we added none. Population ranks are estimates, and city limits do not match metro areas.

Reproduce it. The script is scripts/build-frost-normals.mjs in this site's source; it downloads the Census, gazetteer, station and NOAA files and rebuilds the CSV and chart. Compiled 2026-10-04.

Cite this data

My Planting Zone, "First Frost Dates by City: NOAA 1991-2020 Data for the 100 Largest US Cities," October 4, 2026, https://myplantingzone.com/frost-dates/first-frost-dates-by-city-data/. Underlying data: NOAA National Centers for Environmental Information, U.S. Climate Normals 1991-2020; USDA Agricultural Research Service, 2023 Plant Hardiness Zone Map; U.S. Census Bureau, Vintage 2023 population estimates.

For a single address rather than a city, the ZIP lookup returns your zone, frost dates and a planting calendar, and the last frost guide covers what to plant before the spring date.