The year at a glance
| Month | Mean temperature (F) | Days when the low hits 32 or less | Precipitation (inches) | Snow (inches) | What the roof meets |
|---|---|---|---|---|---|
| January | 32.8 | 22.6 | Ice at the eaves | ||
| February | 35.1 | 20.0 | Snow load and refreezing | ||
| March | 42.5 | 12.4 | Thaw and refreeze | ||
| April | 53.3 | 1.2 | A first look for winter stains | ||
| May | 63.3 | 0.0 | Gutter check | ||
| June | 72.7 | 0.0 | Downpours | ||
| July | 78.2 | 0.0 | Heat on dark shingles | ||
| August | 76.4 | 0.0 | Tropical storm season | ||
| September | 69.2 | 0.0 | Remnants of tropical storms | ||
| October | 57.5 | 0.1 | Leaf fall | ||
| November | 47.0 | 6.0 | The first freezes | ||
| December | 38.0 | 17.5 | Snow arrives |
January and February sit on the freezing line
NOAA's 1991-2020 normals for Newark Airport put January at a mean of 32.8 degrees, with a low of 25.5, and February at 35.1. The low drops to 32 or below on 22.6 days in January and 20.0 in February. Snow adds up to 9.1 inches in January and 10.1 in February.
That is the recipe the Building America Solution Center gives for ice dams: snow on the roof, plus a roof deck warmed above freezing from below by heat escaping the house. Meltwater runs down and refreezes at the cold eave. A New Jersey bulletin on ice barriers applies its rule only to Sussex County, where January averages 25 degrees or lower.
Newark is the station, and weather a few streets over can run different.
March and April: the thaw does the testing
March keeps 12.4 days with a freezing low and 5.6 inches of snow, and April still has 1.2 freezing days. Precipitation climbs to 4.13 inches in March and 3.87 in April.
Water that gets into a small gap during a thaw can freeze again overnight, which is one way a small opening grows. A stain that shows up now may trace back to January's ice or to the shingle that lifted in February.
A good habit for April is the comparison photo: the same slopes, from the same spots, with the date. Patterns that memory misses show up side by side.
May through August: downpours and a hot roof
Newark's wettest monthly normals are July at 4.66 inches, June at 4.34 and August at 4.15. July averages 78.2 degrees, with an average high of 86.9.
Two things matter on the roof in those months. The first is drainage: the Roofing Manufacturers' trade group defines ponded water on a low-slope roof as water that sits 48 hours or longer, and a clogged drain turns a downpour into a pond. The second is heat. The Department of Energy says reflective roofs save the most in hot climates and can add to heating bills in colder ones.
Late summer: Isaias, then Ida
On 4 August 2020, Tropical Storm Isaias cut power to more than a million New Jersey customers; the state weather network says some went without for upwards of five days. It reports countless trees falling and one death from a live power line during cleanup.
Ida's remnants arrived on 1 and 2 September 2021. The same network measured 8.39 inches at Maplewood and 8.44 at Newark Airport, including 3.65 inches in its single heaviest hour at Newark, an hour the network puts at a 1,000-year recurrence interval.
One storm was about wind and trees, the other about rain. A roof gets checked differently after each: limbs and flashing in the first case, ceilings and gutters in the second.
October and November: leaves, then the first freezes
Newark's normals show 0.1 freezing days in October and 6.0 in November, with 3.79 and 3.33 inches of precipitation. That is the window when leaves and shingle grit pack the gutters.
The roofing trade group's post-storm checklist includes gutters that have clogged, and Rutgers works out that 800 square feet of roof shed about 500 gallons through one downspout in a one-inch rain. Water with nowhere to go backs up over the edge, or sits in the trough until the first hard freeze turns it to ice.
December: the first snow load
December's mean is 38.0 degrees, with a low of 31.2, freezing lows on 17.5 days and 5.4 inches of snow.
A UMass Amherst building-technology article says carefully removing snow with a roof rake does help, and warns that scraping can strip granules from asphalt shingles. A rake reaches from the ground. Climbing onto a snowy roof is a job for a roofer, not a homeowner.
When does a seasonal look turn into a phone call?
A stain, a lifted shingle, ice along one eave or a gutter pulling loose is enough. Match the sign to a job on the roof work page, or read the ice dam page first if the trouble is winter's.
Call (862) 358-4524 and describe the sequence as you saw it. Tenants pass the report to the landlord or property manager before a roofer is contacted.