FrostList

When to Prevent Ice Dams in St. Louis, MO

ON TRACK157 days until snow season (estimated)Dec 15

Ice-dam season in St. Louis begins as snow settles near December 15, about 14" a year in the normals; air-seal and insulate the attic ahead of it. The early-odds date runs roughly 13 days ahead of the median, so build in that buffer.

OUTLOOK

Typical first snow season (estimated) near Dec 15; local deadline about Nov 15. The live 10-day outlook loads here.

Local freeze dates for St. Louis

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Oct 24Nov 4Nov 21
28°F (hard freeze)Nov 2Nov 15Dec 4
24°F (severe)Nov 9Nov 26Dec 15

NOAA station: St Louis Sci Ctr · 3.9 mi away · 515 ft elevation.

For St. Louis, the nearest NOAA station with freeze data is St Louis Sci Ctr, 3.9 miles out at 515 feet. Median first-freeze dates there run 32°F by Nov 4, 28°F by Nov 15, 24°F by Nov 26. Year to year the 28°F date has ranged from Nov 2 to Dec 4 — about 32 days apart. Spring's last 32°F freeze clears around Apr 1. Snowfall averages 14 inches a year, first reaching an inch near December.

In St. Louis, freezing nights (32°F) typically begin around Nov 4 and the first hard freeze (28°F) follows near Nov 15. The 32°F date swings from Oct 24 at its earliest to Nov 21 at its latest, near 28 days. The last spring freeze averages Apr 1 and as late as Apr 18, which sets the safe window for reopening outdoor water and de-winterizing gear. At about 14 inches of snow a year, the freeze — not snow load — is the thing to plan around.

Your ice dams checklist

  1. Before snow flies, seal attic air leaks around lights, the attic hatch, and plumbing stacks so warm air stays out of the attic.
  2. Add insulation to bring the attic floor up to a deep, even blanket; a cold roof deck is what stops dams from forming.
    Helpful gear: Attic vent baffles — Recommended pick
  3. Confirm soffit and ridge vents are open and clear so outside air keeps the underside of the roof cold.
  4. After a storm drops four inches or more, rake the lower three to six feet of roof from the ground.
    Helpful gear: 21-foot roof rake — Recommended pick
  5. Keep a safe distance from the edge while raking and never climb an icy roof; work from the ground.
  6. If a dam forms, lay a calcium-chloride melt sock across it to open a drainage channel — do not chip at the ice.
    Helpful gear: Calcium chloride roof-melt socks — Recommended pick
  7. For a roof that dams every year, have heat cable installed at the eaves before the season starts.
    Helpful gear: Roof de-icing heat cable — Recommended pick
  8. Watch for long icicles and interior ceiling stains; both are early signs water is backing up under the shingles.

What to have on hand

21-foot roof rake
Telescoping rake that clears the lower roof edge from the ground.
Recommended pick
Calcium chloride roof-melt socks
Filled tubes laid across the eave to open a drainage channel.
Recommended pick
Roof de-icing heat cable
Zig-zag cable that keeps a melt path open at the eaves.
Recommended pick
Attic vent baffles
Chutes that keep soffit airflow open so the roof stays cold.
Recommended pick

What this means locally

St. Louis freezes close to Florissant (Dec 15) and close to Belleville (Dec 15) — a reminder that even nearby towns differ by days. Statewide, Missouri prep dates run Oct 16 through Nov 15, which is why St. Louis gets its own number rather than a Missouri-wide average. The same freeze also decides when to guard your pipes and ready your snow blower.

Other winter jobs in St. Louis

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

Sprinklers → Nov 5Frozen pipes → Oct 24Car battery → Nov 15Snow blower → Nov 24Sump pump → Apr 1RV → Nov 5Boat → Nov 8Motorcycle → Nov 4

See the full St. Louis winter checklist, in order →

Frequently asked questions

What causes ice dams?
Heat escaping into the attic warms the roof deck and melts the underside of the snowpack. That meltwater runs down to the cold eave, where it refreezes into a ridge of ice. The dam then traps later melt, which can back up under the shingles. University Extension programs point to attic heat loss as the root cause.
How much snow on a roof causes ice dams?
There is no single number, but several inches of snow that lingers gives dams the material they need, especially when days rise above freezing and nights fall below. A roof that sheds snow quickly or stays uniformly cold rarely dams. Watch for snow that sticks around through a stretch of thaw-freeze weather.
Do heat cables prevent ice dams?
Heat cables do not fix the underlying attic-heat problem, but installed in a zig-zag at the eaves they can keep a melt path open so water drains instead of pooling. They work best as one part of a plan that also includes air sealing, insulation, and ventilation. Run them only when needed to save energy.
Is roof raking worth it?
Removing the lower three to six feet of snow from the ground after a storm takes away the material a dam forms from, and it is one of the safest do-it-yourself steps. Use a roof rake with an extension and keep clear of the edge. Never climb onto an icy roof to rake.
Will my insurance cover ice dam damage?
Many homeowner policies cover sudden interior water damage from an ice dam, but coverage and deductibles vary, and repeated damage may raise questions about maintenance. Document the damage with photos. Preventing dams through attic work is cheaper and less disruptive than filing repeat claims.
How do I know if I have an ice dam forming?
Look for a thick ridge of ice at the eaves, large icicles hanging from the gutters, and water stains on interior ceilings or the tops of exterior walls. Icicles alone are not proof, but combined with a warm attic and lingering roof snow they are a warning worth acting on.

Data: NOAA 1991–2020 normals via St Louis Sci Ctr, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.