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After his dog walk Thursday morning, Rich Stack asked me this question.

Temperatures do not need to be below freezing for frost to form:

A unique feature of the gel is that temperatures do not need to reach 32°C to form. Frost can appear on a roof due to a combination of temperature, dew point and humidity.

In Sugar Land the low temperature was 40°, in Richmond it was 39° and in Cypress it was 38°. Yet we have received photos and questions about freezing from all of these areas.

The dew point at each location was in the lower 40s, with humidity near 90%. As the temperature fell below the dew point, moisture in the air condensed into liquid on the roof and began to freeze. Higher humidity made more moisture available to condense and freeze, even if the air temperature was well above freezing.

Additionally, the roofs in these photos were likely much colder than the surrounding air, further encouraging the formation of frost.

What can a patchy frosty roof indicate?

If you notice patchy frost on your roof tomorrow or Saturday morning, this could be a warning sign. This may indicate insufficient attic insulation, with heat escaping from your home in certain areas and melting the gel. If you notice this, it’s a good idea to have your insulation checked by a professional.

This question came to us through click2houston.com help desk. If you have a weather question, you can submit it here or email me directly at [email protected]. I would also like to see your weather photos: share them with us at Click2houston.com/pins.