FrostList

When to Test Your Sump Pump in Longmont, CO

SEASON PASSED300 days until spring thaw test (last 32°F)May 7

Two moments stress a Longmont sump pump: the spring thaw near May 7 and the fall rainy season, so test before each with a five-gallon bucket in the pit. The early-to-late range spans roughly 25 days, so treat the median as a midpoint, not a promise.

OUTLOOK

Typical first spring thaw test (last 32°F) near May 7; local deadline about May 7. 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 sump pump checklist

  1. Pour about five gallons of water into the pit slowly and watch the float rise, the pump start, and the water drop.
    Helpful gear: Water level alarm — Recommended pick
  2. Confirm the discharge line carries water 10–20 feet from the foundation and does not drain back into the pit.
    Helpful gear: Sump check valve — Recommended pick
  3. Clear the inlet screen and the pit of gravel and debris that can jam the float or the impeller.
  4. Check the check valve for a firm click; a failed valve lets discharged water fall back and short-cycle the pump.
  5. Add a battery backup pump so the system still runs when a storm knocks out the power.
    Helpful gear: Battery backup sump pump — Recommended pick
  6. Test the backup on battery power and note the install date; batteries usually need replacing every few years.
  7. If the primary pump is 7–10 years old, keep a replacement on the shelf before it fails mid-storm.
    Helpful gear: Replacement primary pump — Recommended pick
  8. Remember that flood insurance and most homeowner policies treat pump failure separately — read your coverage.

What to have on hand

Battery backup sump pump
Second pump that runs when the power goes out mid-storm.
Recommended pick
Water level alarm
Loud sensor that warns you before the pit overflows.
Recommended pick
Sump check valve
One-way valve that stops discharged water from draining back.
Recommended pick
Replacement primary pump
A ready spare for a pump nearing the end of its life.
Recommended pick

What this means locally

Against its neighbors, Longmont (first freeze May 7) runs close to Boulder (May 6) and close to Loveland (May 10). Across Colorado, local prep deadlines in our data range from Apr 14 to May 10, so a statewide rule of thumb would miss Longmont by weeks. In Longmont, that same cold is your cue to protect your pipes.

Other winter jobs in Longmont

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

Sprinklers → Oct 2Frozen pipes → Sep 23Car battery → Oct 12RV → Oct 2Boat → Oct 5Motorcycle → Oct 5

See the full Longmont winter checklist, in order →

Frequently asked questions

How do I test my sump pump before heavy rain?
Pour about five gallons of water into the pit slowly and watch the float rise, the pump switch on, and the water level drop. Confirm the discharge carries water well away from the foundation. Doing this before the wet season, and again in spring near the last freeze around May 7, catches problems early.
How often should a sump pump run?
It varies with your water table and weather; some pumps cycle every few minutes during a storm and sit idle for weeks in dry spells. Frequent cycling with no rain can signal a stuck float, a failed check valve, or groundwater seeping in. Occasional running during wet weather is normal.
How long do sump pumps last?
A typical sump pump lasts about 7 to 10 years, though hard-working pumps wear out sooner. If yours is near that age, keep a replacement on hand so a mid-storm failure does not leave the pit unattended. Testing it seasonally tells you more than age alone.
Do I need a battery backup sump pump?
If your basement floods when the power goes out, yes — storms that overwhelm the pit are exactly when the grid tends to fail. A battery backup runs the pump through an outage, which is the single most common cause of a wet basement during heavy weather. Test the backup on battery power, too.
Does insurance cover sump pump failure?
Standard homeowner policies and federal flood insurance often exclude damage from a sump pump that fails or is overwhelmed. A separate water-backup or sump-failure rider may be available. Read your policy before a storm, because assumptions about coverage are a common and costly surprise.
Why is my sump pump running with no rain?
A high water table, snowmelt, or groundwater seepage can keep the pit filling even in dry weather. A pump that runs constantly may also have a stuck float switch or a check valve that lets discharged water fall back into the pit. Check the float and the valve first.

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