FrostList

When to Prevent Ice Dams in Florissant, MO

ON TRACK157 days until snow season (estimated)Dec 15

With about 17" of snow a year in Florissant, ice dams are a real risk once the roof holds snow — around December 15 in the normals — and the fix, attic sealing and insulation, happens before then. Year to year the date swings about 28 days, which is why the live outlook beats the calendar.

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 Florissant

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Oct 23Nov 4Nov 18
28°F (hard freeze)Nov 2Nov 13Nov 30
24°F (severe)Nov 8Nov 24Dec 11

NOAA station: St Louis Lambert Intl AP · 3.7 mi away · 531 ft elevation.

Numbers for Florissant come from St Louis Lambert Intl AP, 3.7 miles away at 531 feet, where the medians fall 32°F by Nov 4, 28°F by Nov 13, 24°F by Nov 24. The 28°F freeze has come as early as Nov 2 and as late as Nov 30, a 28-day spread. Spring's last 32°F freeze clears around Apr 2. Snowfall averages 17 inches a year, first reaching an inch near December.

In Florissant, freezing nights (32°F) typically begin around Nov 4 and the first hard freeze (28°F) follows near Nov 13. Year to year, the first 32°F night has fallen anywhere from Oct 23 to Nov 18 — about 26 days apart. Spring's final freeze lands near Apr 2 and as late as Apr 17, so that is when outdoor water and stored gear can safely come back online. Snowfall averages roughly 17 inches a year — enough that a working snow blower and a clear roof edge earn their keep.

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

Compared with nearby cities, Florissant's first-freeze date near Dec 15 sits close to St. Charles (Dec 15) and close to St. Louis (Dec 15). Missouri's deadlines span Oct 16 to Nov 15 statewide — one date for all of Missouri would be off by weeks for Florissant. Once you know Florissant's freeze date, use it to guard your pipes and ready your snow blower too.

Other winter jobs in Florissant

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

Sprinklers → Nov 3Frozen pipes → Oct 23Car battery → Nov 13Snow blower → Nov 24Sump pump → Apr 2RV → Nov 3Boat → Nov 6Motorcycle → Nov 4

See the full Florissant 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 Lambert Intl AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.