When to Winterize Plumbing: Median First and Last Freeze Dates for 46 US Cities

The dates this is built on

NOAA publishes the median date of first and last freeze for long-record weather stations as part of its climate normals. That is the date by which half of years have seen a minimum temperature at or below 32F. It is the closest thing to a published answer to when freeze protection has to be finished.

One thing to be clear about before using any of these dates: a median is not a deadline. In half of all years the first freeze arrives earlier than the date shown.

Freeze dates and season length, 46 cities

Ordered by length of the freeze season. The 28F columns are included because hard freezes, not marginal ones, are what burst pipes.

Source: NOAA National Centers for Environmental Information, 1991 to 2020 climate normals. Season length calculated by The Plumbing Brief. Four of the 50 metros analysed have no computable season because a median freeze date does not occur and are omitted from this table.

The evidence

1. Earliest median first freeze: Denver, 6 October. Source: NOAA 1991 to 2020 normals.
2. Second earliest: Minneapolis, 10 October, then Hartford 13 October. Source: NOAA normals.
3. Latest median last freeze: Denver, 6 May. Source: NOAA normals.
4. Longest freeze season: Denver, 212 days. Source: calculated from NOAA normals.
5. Second longest: Minneapolis, 197 days, then Hartford 193 and Rochester 192. Source: calculated from NOAA normals.
6. Chicago: first freeze 19 October, last 22 April, season 185 days. Source: NOAA normals.
7. New York: first freeze 11/18, last 04/01, season 134 days. Source: calculated from NOAA normals.
8. Shortest computable season: San Francisco, 1 day. Source: calculated from NOAA normals.
9. Orlando: first freeze 6 January, last 20 January, season 14 days. Source: NOAA normals.
10. Tampa: season 11 days, 4 January to 15 January. Source: NOAA normals.
11. Phoenix: season 4 days, 2 January to 6 January. Source: NOAA normals.
12. Las Vegas: season 49 days, 11 December to 29 January. Source: NOAA normals.
13. New Orleans: season 43 days, 21 December to 2 February. Source: NOAA normals.
14. Cities with no computable median freeze date: 4 of 50, including Los Angeles and San Diego. Source: NOAA normals.

What the numbers imply

The window for winterizing is shorter than the freeze season suggests

Formula. Median first freeze date, treated as the midpoint of a distribution rather than a start date.

Finding. By definition, half of years see a first freeze before the median date. Denver’s median first freeze is 6 October, which means in roughly one year in two the first freeze has already happened by then. Work scheduled to complete on the median date is late in half of all years.

Limitations. NOAA publishes first-freeze dates at several probability levels, including the 10 percent and 20 percent thresholds that would give an earlier and safer planning date. This page reports the median only, and anyone planning operationally should use the lower-probability dates from the same source.

Southern cities have long seasons and almost no freezes

Formula. Freeze days per year divided by freeze season length, per city.

Calculation. Denver: 156.9 freeze days across a 212 day season, a ratio of 0.74. Orlando: 2.3 freeze days across a 14 day season, 0.16. Las Vegas: 3.1 across 49 days, 0.06.

Finding. Northern cities freeze on roughly three days in four of their freeze season. Las Vegas freezes on about one day in sixteen of its. A long season with few freezes is the hardest pattern to prepare for, because the risk period is wide but the events are rare enough to be discounted.

Limitations. The ratio is sensitive to small numbers in low-freeze cities, where a difference of one or two freeze days moves it substantially.

The 28F dates compress the window further

Formula. Compare median first 32F and first 28F dates per city.

Finding. The 28F threshold arrives later and ends earlier than the 32F threshold in every city where both are published. Because marginal freezes rarely burst pipes, the 28F window is closer to the period of genuine plumbing risk, and it is materially shorter than the 32F season in southern cities.

Limitations. 28F is a convenient published threshold, not a pipe failure point. Failure depends on duration, insulation and pipe position, none of which this data contains.

Download the data

Freeze dates, season length and freeze-day counts for all 50 metros analysed, published as a CSV under a Creative Commons Attribution 4.0 licence. Attribution: The Plumbing Brief.

Freeze dates and freeze days by metro (CSV)

How this report was built

Methodology

Source. NOAA National Centers for Environmental Information climate normals for 1991 to 2020, retrieved 2 October 2026. One primary long-record station per metropolitan area; station identifiers are in the CSV.

Fields used. Median date of first and last occurrence of a minimum temperature at or below 32F and at or below 28F, and average annual days at or below 32F.

Season length. Days between median first and median last 32F date. Where the first freeze falls in the second half of the calendar year, the last freeze is taken as the following year.

A correction made during the build. An earlier version assumed the last freeze always fell in the following calendar year. For cities where both median dates fall in the same January, that produced impossible season lengths, including 380 days for Orlando. The published Orlando figure is 14 days.

Exclusions. Four metros return no median freeze date and are omitted from the table rather than shown as zero.

Retrieval date. 2 October 2026.

Data limitations

• A median is not a deadline. Half of years see a first freeze earlier than the date shown. Operational planning should use NOAA’s 10 or 20 percent probability dates instead.
• One station represents a whole metro. Suburbs and inland areas usually freeze earlier and more often than the primary station.
• Normals are 30-year averages and exclude extreme single events by construction.
• A date threshold says nothing about how long temperatures stay below freezing, which is what determines pipe failure.
• Building construction, insulation and pipe routing are not in this data.
• Season length is derived from two median dates and is not the same as a continuous period of freezing risk.
• This page reports climate data. It is not plumbing guidance, and freeze protection decisions should be made with a qualified plumber for the specific building.

Source quality ranking

Tier 1. NOAA National Centers for Environmental Information, 1991 to 2020 climate normals.

Tier 2. None used. Tier 3. None used.

Excluded. Regional rules of thumb for winterizing dates that cite no temperature record.

Figures worth quoting

• Denver’s median first freeze is 6 October, the earliest of 46 US cities.
• Denver’s freeze season runs 212 days. Phoenix’s runs four.
• Half of all years see a first freeze before the median date, so the median is not a deadline.
• Northern cities freeze on three days in four of their season. Las Vegas freezes on one day in sixteen.
• Four of 50 major metros have no median freeze date at all.

Briefing note

The median first freeze of the year arrives on 6 October in Denver, 10 October in Minneapolis, 19 October in Chicago and 6 January in Orlando, according to NOAA 1991 to 2020 climate normals covering 46 US cities with a computable freeze season. Denver has both the earliest first freeze and the longest season at 212 days, running to a median last freeze on 6 May. At the other end, Phoenix has a four day season and San Francisco a single day. Because these are medians, half of all years see a first freeze earlier than the date shown, which means freeze protection scheduled to complete on the median date is late in one year in two. Southern cities show the pattern hardest to prepare for: Las Vegas has a 49 day freeze season containing roughly three freeze days.

How reporters could frame this

1. Denver’s first freeze arrives in the first week of October
2. The median first freeze date is not a deadline, it is a coin flip
3. Phoenix has a four-day freeze season and Denver has 212
4. The hardest cities to winterize are the warm ones
5. When freeze risk starts in each of 46 US cities

Related questions

When should I winterize my plumbing? Before the median first freeze date for your city, which this table publishes. Denver is 6 October, Chicago 19 October, New York 18 November, Orlando 6 January. Because half of years freeze earlier than the median, finish the work before that date.

When is the first freeze in Denver? The median first 32F date is 6 October, the earliest of the cities analysed.

When is the first freeze in Chicago? 19 October on the median, with the last on 22 April, a 185 day season.

How long does freeze risk last? From 212 days in Denver down to four days in Phoenix. Forty-six of 50 metros have a computable season.

Which cities have no freeze season? Four of the 50 analysed return no median freeze date, including Los Angeles and San Diego. That means freezing is too rare to produce a median, not that it never happens.

Is 32F the temperature pipes freeze at? Water freezes at 32F but pipes usually do not fail at marginal freezes. This page also reports 28F dates, which sit closer to the period of genuine risk, though neither threshold is a failure point.

Why does the median date understate risk? By definition half of years see a first freeze before it. NOAA publishes 10 and 20 percent probability dates from the same data, which give earlier and safer planning dates.

Do suburbs freeze at the same time as the city? Generally no. Each figure here comes from one primary station, and outlying and inland areas usually freeze earlier and more often.

Which city is hardest to prepare for? On this data, the warm cities with long thin seasons. Las Vegas has a 49 day freeze season containing about three freeze days, so risk is spread across weeks but rare enough to be discounted.

Does this tell me whether my pipes will freeze? No. It reports climate exposure only. Duration below freezing, insulation, pipe location and water movement all matter and none are in this dataset.

How to cite this report

The Plumbing Brief, “When to Winterize Plumbing: Median First and Last Freeze Dates for 46 US Cities”, https://theplumbingbrief.com/when-to-winterize-plumbing-by-city/, accessed [date].

Last reviewed: 2026-10-02.