FrostList

When to Prevent Frozen Pipes in Longmont, CO

ON TRACK86 days until first freezing night (32°F)Oct 5

In Longmont, plan for freezing nights from about October 5 onward — one year in ten by September 23 — and treat any low in the low 20s as a pipe-risk night. The early-to-late range spans roughly 25 days, so treat the median as a midpoint, not a promise.

OUTLOOK

Typical first first freezing night (32°F) near Oct 5; local deadline about Sep 23. The live 10-day outlook loads here.

Local freeze dates for Longmont

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 23Oct 5Oct 16
28°F (hard freeze)Sep 30Oct 12Oct 25
24°F (severe)Oct 6Oct 21Nov 5

NOAA station: Longmont 2 Ese · 1.3 mi away · 4,950 ft elevation.

Longmont draws its numbers from Longmont 2 Ese, 4,950 feet up and 1.3 miles away. Its median first-freeze dates are 32°F by Oct 5, 28°F by Oct 12, 24°F by Oct 21. The 28°F freeze has come as early as Sep 30 and as late as Oct 25, a 25-day spread. Spring's last 32°F freeze clears around May 7.

Longmont usually sees its first 32°F night about Oct 5, with the first 28°F hard freeze close behind near Oct 12. That first freezing night has ranged from Sep 23 to Oct 16, roughly a 23-day spread. On the spring side, the last 32°F freeze clears around May 7 and as late as May 22 — the green light for reopening water and de-winterizing. With almost no snow in a normal year, cold — not plowing — sets the calendar, and it centers on May 7.

Your frozen pipes checklist

  1. Disconnect, drain, and store garden hoses, then shut off and drain any interior valves that feed outdoor faucets.
  2. Insulate exposed pipes in the garage, crawl space, and along exterior walls with foam sleeves rated for the pipe size.
    Helpful gear: Foam pipe insulation sleeves — Recommended pick
  3. On nights in the low 20s, let a pencil-thin stream of water drip from the faucet farthest from where the line enters.
  4. Open cabinet doors under kitchen and bathroom sinks on outside walls so household heat reaches the plumbing.
  5. Add self-regulating heat cable to the runs most likely to freeze, such as a pipe in an unheated garage.
    Helpful gear: Self-regulating heat cable — Recommended pick
  6. Cap outdoor faucets with insulated covers once the hoses are off.
    Helpful gear: Outdoor faucet covers — Recommended pick
  7. Know where your main shutoff is and confirm it turns; a fast shutoff limits water damage if a line lets go.
  8. If you travel, keep the thermostat at 55°F or higher and ask someone to check the house during a cold snap.
    Helpful gear: Wi-Fi water leak sensor — Recommended pick

What to have on hand

Foam pipe insulation sleeves
Split foam tubing for exposed pipes in crawl spaces and garages.
Recommended pick
Self-regulating heat cable
Thermostatic cable that warms vulnerable runs only when it is cold.
Recommended pick
Outdoor faucet covers
Insulated caps for hose bibs once the hoses come off.
Recommended pick
Wi-Fi water leak sensor
Puck that pings your phone the moment it senses water.
Recommended pick

What this means locally

Against its neighbors, Longmont (first freeze Oct 5) runs close to Boulder (Oct 5) and later than Loveland (Oct 1). Across Colorado, local prep deadlines in our data range from Sep 15 to Oct 11, so a statewide rule of thumb would miss Longmont by weeks. In Longmont, that same cold is your cue to shut down your sprinklers and check your car battery.

Other winter jobs in Longmont

Every task below is dated to Longmont's own freeze and snow normals.

Sprinklers → Oct 2Car battery → Oct 12Sump pump → May 7RV → Oct 2Boat → Oct 5Motorcycle → Oct 5

See the full Longmont winter checklist, in order →

Frequently asked questions

At what temperature do pipes freeze?
Pipes generally come under risk when the temperature outside falls to about 20°F, the threshold many guides use for taking action. Pipes in unheated or exterior-wall spaces freeze sooner than well-insulated interior runs. Wind and poor insulation lower the effective temperature, so a windy night in the mid-20s can be as risky as a still night in the low 20s.
Should I drip my faucets tonight in Longmont?
If the overnight low is forecast at or below about 20°F, letting a thin stream run from the faucet farthest along the line is a low-cost precaution. Moving water is slower to freeze and relieves pressure. Check tonight's low against the live outlook above; freezing nights here typically begin around Oct 5.
How long does it take for pipes to freeze?
There is no fixed clock; it depends on pipe location, insulation, and how far below freezing the air drops. An exposed pipe in a windy, unheated space can freeze in a matter of hours during a hard cold snap, while a protected interior pipe may never reach freezing. The colder and windier it is, the faster it happens.
Which pipes freeze first?
The most exposed pipes freeze first: outdoor hose bibs, and lines in unheated garages, crawl spaces, attics, and along exterior walls. Pipes under sinks on outside walls are common trouble spots. That is why disconnecting hoses and opening cabinet doors on cold nights are two of the highest-value steps.
Does homeowners insurance cover burst pipes?
Sudden, accidental water damage from a frozen pipe is often covered, but insurers may deny a claim if the home was left unheated or the damage is judged to be from neglect. Coverage varies by policy. Keeping the heat on and taking reasonable precautions helps protect both your home and your claim.
What temperature should I keep my house if I'm away?
A common recommendation is to keep the thermostat no lower than 55°F while you are away so interior walls stay warm enough to protect the plumbing. Leaving cabinet doors open and having someone check the house during a cold snap adds a margin of safety, especially for pipes on exterior walls.

Data: NOAA 1991–2020 normals via Longmont 2 Ese, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.