Guide

Right outsideWeather

Why static shocks come back every winter

December to March

Static shocks from doorknobs, car doors and hats come back every winter because the air is dry. Cold outdoor air holds very little water, and heating it indoors adds none, so the charge you pick up from clothes has nowhere to leak away.

Why this time of year

The driest air of the year sits over eastern Massachusetts from December through March. NOAA's 1991-2020 hourly normals for Boston Logan put the average dew point in those four months at about 18-25 F, against about 61-62 F in July and August. Once that air is warmed indoors its relative humidity drops even lower, so static builds and then snaps.

How to notice it

  1. Pull off a wool hat and watch your hair stand up. Every strand carries the same charge, so they push away from each other.
  2. Walk across a rug in socks or slippers, then reach for a metal doorknob and listen for the small snap.
  3. Try it again holding a metal key and touch the key to the knob first. The charge flows out through the key, so your fingertip feels nothing.
  4. Notice how the shocks fade in a room running a humidifier, where the damper air lets the charge leak off.

Try this with kids: Hold a key, touch it to the doorknob before your hand does, and see if you can beat the zap.

Phrase to know: “Dew point”: the temperature at which air is full of water and dew or frost starts to form, so a low dew point means the air holds very little moisture.

Safety

  • At the gas pump, stay outside the car while fuel is flowing. Getting back in can build a static charge that sparks when you touch the nozzle again, and cold, dry weather makes static worse. If you do get back in, touch metal on the outside of the car, away from the filler, before you take hold of the nozzle.

Sources

  • pa.uky.eduUniversity of Kentucky Physics: contact moves electrons; a thin water film carries charge away in humid air and does not form when indoor humidity is low; heating does not change the amount of water in the air. 'When the humidity inside is low, the conducting film does not occur, and we start getting static shocks.'
  • mcgill.caMcGill Office for Science and Society: humidity is the number one factor; heating lowers relative humidity; hair stands on end because strands repel; humidifier helps; touching a key or coin to metal drains the charge.
  • ncei.noaa.govNOAA NCEI 1991-2020 hourly normals, Boston Logan, HLY-DEWP-NORMAL. Monthly means averaged by the sourcing agent: Jan 18.5, Feb 19.0, Mar 24.9, Dec 24.8, Nov 33.1, Apr 34.6, Jul 61.7, Aug 61.1 F.
  • ucanr.eduUC ANR Safety Note 25: static a significant cause of fueling fires 'particularly in cold, dry weather'; do not re-enter the vehicle while fueling; touch metal away from the fueling point before the pump handle.

Checked against these sources on November 3, 2026.

In the guide for December, January, February, March

Also worth noticing