Ice dam risk in Hannibal, MO
How often ice dams form in Hannibal
8.4 dam days a winter
Moderate risk. On an ordinary house in Hannibal, conditions for an ice dam come on about 8.4 days in a normal winter, mostly in January and February.
Hannibal averages 16 inches of snow a year and about 31 days with snow on the ground. Most of it comes and goes within a few days. The conditions that make a dam need all three at once: snow, cold at the eave and heat above it.
What your attic does to that number in Hannibal
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 4.9 | Low |
| Typical, some insulation, not air-sealed | 8.4 | Moderate |
| Older or poorly insulated, warm attic | 12.7 | Moderate |
Sealing and insulating a typical attic takes out about 3.5 days a winter here. It drops the risk from moderate to low. An older house with a warm attic should expect closer to 12.7 days.
What to do about ice dams in Hannibal
- Air-seal the attic floor: the gaps around the hatch, light fixtures, plumbing stacks and the top plates of interior walls. This is the fix that removes the cause, and it usually costs less than a season of contractor ice removal.
Which to spend on first: air sealing or heat cable.
Hannibal winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 4.6 | 11.8 | 3.8 |
| February | 5.0 | 8.1 | 2.1 |
| March | 1.9 | 2.8 | 0.4 |
| April | 0.2 | 0.2 | 0.0 |
| November | 0.8 | 0.5 | 0.1 |
| December | 3.1 | 7.5 | 1.9 |
Hannibal next to nearby towns
Hannibal ranks 2 of 80 Missouri cities here for ice-dam days, behind Maryville at 9.3 days.
- Quincy, IL 15 mi, 6.7 days
- Mexico, MO 46 mi, 6.3 days
- Troy, MO 56 mi, 3.5 days
- Moberly, MO 59 mi, 2.9 days
- Jacksonville, IL 62 mi, 6.3 days
Where these numbers come from
NOAA 1991–2020 climate normals from Bowling Green 1 E, 27.9 miles from Hannibal. A dam day is a day with snow on the roof and freezing at the eave while heat or sun melts the snow above it. This describes a normal winter, not this one.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.
- The weather station is 28 miles away, far enough that local snow can differ.