Atmospheric Pattern Goes Negative, We Get Chilly As A Result

A gloomy, chilly spring day, May 3, 2019.  A weather 
pattern setting up now is forecast to give us more than
our fair share of weather like this. 

Something called the negative NAO is going to ruin your spring. For a while, anyway. 

Our upcoming bout of generally chilly spring weather is brought to you by a negative phase of something called the North Atlantic Oscillation.

This refers to changing weather and pressure patterns in the North Atlantic.  When it goes negative we get colder. 

It's now going negative.  A negative NAO means that high pressure takes residence up in and near Greenland. This suppresses the jet stream southward, especially in eastern North America. When the jet stream slips south, we get colder. 

In the winter, a negative NAO means subzero weather and a risk of nasty nor'easters in New England. 

This time, it's all happening in late April and the opening week or two of May, so it won't be a dramatic as a negative NAO in the winter.  It'll just be chilly most days between now and at least the first week in May. Not every day will be colder than normal, but the trend will go in that direction. 

Most, but not all of the time, it doesn't rain (or snow) all that much in a negative NAO around here during the spring. We get a lot of cloudy days and light showers, but blockbuster storms tend to be lacking in this regime. 

The very cloudy weather with this pattern in spring is in large part due to the interaction of the strong spring sun and the nippy atmosphere. The sun heats the ground strongly causing updrafts. Those updrafts form lots of clouds as they rise into the colder air.  The colder air causes moisture in the updrafts to condense, and you get clouds.  

This weather pattern does have its benefits, at least elsewhere in the nation.  The negative NAO tends to suppress severe thunderstorms and tornadoes in the Midwest. That's a good thing as we head toward the peak of severe weather season.

This doesn't mean there won't be tornadoes. It just means there will be fewer of them. 

The weather pattern is also causing some late season rain and mountain snow in California. It won't be a huge amount of precipitation out there, but anything will come in handy after a remarkably dry second half of winter in much of the western U.S.

Back here in Vermont, the next few days will be only slightly cooler than average. We will get a quick squirt of warmer than  normal air Monday and Monday night before we settle into the cool pattern again.