By: Al Kaprielian – Dec. 2016
Welcome to the start of meteorological winter which goes through the month of February. Now that November is over, so is this year’s hurricane season. The end of November saw some episodes of heavy rain making a dent in our drought, however, not eliminating it.
With a large contrast in air masses, there were outbreaks of tornadoes over the southern states. Temperatures for November did run a little above normal. Now with December and the shorter hours of daylight we will see the colder air start to get stronger. Some of this cold air will start to move into our region during the first half of the month. As the colder air moves down from Canada, it will start to clash with warmer air across the southern states.
This will start the process of low pressure systems forming over the Gulf of Mexico/ off the east southeast coast of the US. As I have mentioned in past articles it will all depend on how much phasing occurs with the northern and southern streams of the jet stream.
When these two streams join together we see these low pressure systems move farther north, closer to our region, to bring rain/snow/ mixture or even freezing rain. Also with storms to our south, we look to see if there are any high pressure systems to our north or northeast. If there are, then this could lead to more snow or mixed “precip” (precipitation). When high pressure is located over the Canadian Maritimes, this provides cold air at the surface. If warm air is aloft this can lead to mixed “precip” or even freezing rain. There is a difference between mixed “precip” (sleet) and freezing rain. Freezing rain occurs when temperatures above the ground are all above freezing 32 degrees. Temperatures at the ground are near or below 32 degrees.
Freezing rain falls as a liquid like regular rain and the drops freeze after they hit the ground. Sleet occurs when a warm layer forms in the upper atmosphere and the snowflake melts in this warm layer and then refreezes below this warm layer into an ice pellet called sleet which is in a solid form. Snow occurs when temperatures at all levels above the ground are below 32 degrees. In a snow situation the temperatures at ground level can be above 32 degrees. If we have arctic air over us during a winter storm then the snow will be dry low water content. This will cause the snow to be fluffy and contain less weight.
When we do not have cold arctic air over us, the snow can contain more water and will be heavier. This will be a wet snow and due to the weight can cause tree branches and power lines to fall causing power outages. A similar situation occurs with the ice for freezing rain as the ice can build up on trees and power lines causing power outages. So this winter be prepared for winter storms before they occur; have enough food, especially non-perishable food.
Have plenty of bottled water. Always be prepared before a winter storm occurs because once it begins road conditions can worsen very quickly. Also with winter storms, their track is critical due to us being so close to the warmer ocean waters.
Remember the ocean does not cool as fast as the land during the fall and early winter. If a storm, for example, tracks over Worcester the counter clockwise flow around the low pressure system will bring air off the warmer ocean waters and rain will occur along the coast. Further inland more sleet and snow will occur. Some low pressure systems during the winter will track farther south outside the 40 north latitude 70 longitude. With this track Cape Cod & the New England south coast would get the highest snowfall amounts as they will be closer to the storm.
If the storm is intense, these areas will see gusty to strong winds during the storm causing blizzard conditions. With the counter clockwise circulation around low pressure systems this causes warmer air on the east side of the low, off the warmer ocean. The cold side of a low pressure system is the west/northwest side of the low causing a more northerly wind bringing cold air down from Canada. This causes most of the heaviest snows to occur on the west/northwest side of the storm. Living by the ocean makes the track of a winter storm critical in forecasting snowfall amounts.
Also the intensity of the storm affects how much snow we get. Lastly, we look at the speed of the storm which affects how much snow we get. If the storm is moving fast less snow will occur. An example is the Blizzard of 1978 where the storm stalled in the Atlantic Ocean causing snow to fall for a couple of days. Next month we will recap the weather in December and take another look at winter weather.