October in Pueblo: The Exact Week to Winterize Your Cooler, From the NWS Freeze Tables

September 8, 2026

If you want one answer: the week of September 28 through October 4 is when a swamp cooler in the City of Pueblo should be drained and shut down. That is not a guess or a rule of thumb. The National Weather Service office in Pueblo publishes freeze probability dates for Pueblo Memorial Airport, and that week sits exactly between the date a 36 degree night becomes more likely than not and the date a 32 degree freeze does. Everything else on this page is how to adjust that week for where you actually live and what to do inside it.

The published table

Here is what NWS Pueblo publishes for the airport, at 4,692 feet. Each row gives the date by which there is a 50 percent chance and a 90 percent chance, respectively, of hitting that temperature:

Three thresholds, three different jobs.

36 degrees is the warning shot. Nothing in the cooler freezes at 36, but the airport reading is taken in a shelter roughly five feet above the ground, and that is not where your cooler lives. A flat roof radiating heat to a clear sky on a calm night gets colder than the official number, and so does an exposed quarter-inch copper line running across it. When the official low is 36, parts of the system have been at or below freezing. September 27 is the date to have the shutdown scheduled, not the date to start thinking about it.

32 degrees is the real deadline. October 5 at 50 percent, October 20 at 90 percent. A cooler drained after October 5 has been rolling dice; a cooler still full on October 20 has almost certainly taken a freeze.

28 degrees is what actually breaks things. A brief touch of 32 may do nothing. A sustained 28 degree night is what expands water hard enough to split copper and crack a polymer pump housing. October 13 at 50 percent, October 27 at 90 percent.

Why the week is the last of September, not the middle of October

A homeowner reading that table could reasonably conclude they have until October 5. Two things argue against it.

The first is the gap between a thermometer and a roof. Official climate data is measured in a standardized shelter over a standard surface. The exposed run of supply line on a Pueblo roof, the metal pan, and the float valve sitting in standing water all lose heat faster than that shelter does. Practically, subtract a few degrees.

The second is scheduling. Everyone in this city reads the same forecast on the same evening, and when the first cold night appears in the ten-day, the phone does not stop. A shutdown booked in the last week of September is a scheduled visit at $100 to $200. Wait until the afternoon a hard freeze shows up in the forecast and everyone is calling at once, and whatever does not get drained that night turns into an April repair.

Adjusting for elevation

The airport table is a Pueblo number. The service area spans about 2,300 feet of elevation, and the freeze calendar spans it too.

For a sense of how much altitude moves those dates, NWS Pueblo publishes the same table for Alamosa, at over 7,500 feet in the San Luis Valley: 36 degrees at August 31 and September 17, 32 degrees at September 14 and September 28, 28 degrees at September 21 and October 2. That is roughly a month earlier than Pueblo for every threshold. Alamosa is an extreme case because cold air pools in that valley, but the direction is unambiguous.

Here is a sensible shutdown order by town, from highest to lowest:

Those windows for the higher towns are an elevation-based rule of thumb, not published NWS dates for those towns. The published dates are the airport’s. But nobody at 6,800 feet in the Wet Mountains should be working off a 4,692 foot table.

The steps that cannot wait, and the ones that can

Some of the shutdown is urgent and some of it is not, which matters on an evening when the light is going.

Do these before the first freezing night, in this order:

1. Shut the water off at the source. Close the hose bib or saddle tap that supplies the cooler; closing the float alone does not count.
2. Drain the supply line. Skip this step and it will cost you. That quarter-inch copper or poly line running up the wall and across the roof is the part that splits, and shutting the float without emptying the line leaves it full. Open it at both ends and confirm it is empty.
3. Drain the pan. Pull the plug or open the drain fitting, then sponge the rest. Water left in there turns to ice, swells, and pries at the seams and the drain fitting until they leak. While it is wet, scrape the loose scale out; on Pueblo Water’s published average hardness of 10.5 grains per gallon a season leaves a real crust, and it comes off far easier now than in April.
4. Pull the aspen pads. They are finished after a season on this water, and left in place they hold damp against the pan all winter.

These can wait a week if they have to: fitting the exterior cover, sealing the duct damper, and covering the interior ceiling grille. They matter for your heating bill and for keeping grit out over the winter, but they will not crack anything.

What it costs to get it wrong

A split supply line is $100 to $400 to replace depending on the run. It rarely travels alone: a float valve that froze is $100 to $250, and a cracked pump housing is $150 to $400 installed. That is how a missed shutdown turns into a $300 to $600 April visit, against $100 to $200 for the fall shutdown done on time. Booked with the spring start-up as a package, the pair runs $200 to $400. Every one of those numbers is on the pricing page.

The worse outcome is the pan. Let water freeze in a galvanized pan that was tight in September and it may be seeping by spring, and since the pan is the body of the cooler, there is no swapping it out. On the decades-old original units still working in Belmont, Sunset Park, and Eastwood Heights, one missed October is how a repairable cooler becomes a $1,500 to $4,000 replacement.

If you are still cooling into October

Some years you want the cooler through the first week of October, and that is fine. The move is to watch the NWS Pueblo forecast every evening from about September 25 onward, and when a night in the low 30s appears in the seven-day, do steps one through four that afternoon. Leave the cover and the damper for the weekend if you need to.

And if the cooler quits in that last warm week rather than shutting down gracefully, the warm air page covers the five-minute check, and the repair cost calculator will give you a range before you decide whether it is worth fixing this late in the season.