Boston winter weather event, Jan 17-19, 2010

Jan 17, 7 pm EST

Snowfall map, dynamic link
Snowfall map, static link

Snowfall events were generally light in eastern Massachusetts. Much of the precipitation that occurred fell in other forms. Examine the observations at Logan Airport. In the "Wx" column, the observer reports if he has seen rain (RN), snow (SN), or other types or precip. During this storm there were a lot of types!

Preciptation types

The type of precipitation that arrives at the surface depends on the vertical temperature structure of the atmosphere. Precipitation starts as snow in the cloud, but may go through a transformation as it falls to the ground.

	Snow. Temperature is cold all the way to the surface.
	Rain. Warm air reaches down to the surface.
	Sleet. Snow passes through shallow layer of warm air aloft and melts into rain. Then it passes through a layer of cold air near the ground, where it refreezes into pellets of ice.
	Freezing Rain. Snow passes through a layer of warm air aloft and melts into rain. A very shallow layer of cold air exists near the surface, but there isn't time to freeze into pellets before it hits the ground. The rain freezes on the ground and other surfaces on contact.

Vertical temperature soundings

Plot vertical temperature sounding data. Directions: under "Type of Plot", click "GIF: to 700 mb" to plot temperature in the lower atmosphere. Select the date and time of observations. Then click on the map for your location (CHH - Chatam, MA is the closest to Boston). You will get a plot in a new window with temperature in Celsius on the x-axis, and pressure in mb on the y-axis. The thick black lines are the temperature and dewpoint.

Winter weather safety

Safety and awareness page
Preparedness guide