By: Al Kaprielian – May, 2016
After seeing some warm April days with temperatures in the 70’s to low 80’s, our weather has turned noticeably cooler as we moved into May. In this article we will be explaining why, and also some other weather features that can occur during the spring months.
This past winter did not feature much snow and temperatures ran warmer than normal.
This was somewhat due to El Nino, which occurs when the ocean waters of the South Pacific Ocean are warmer than normal. This causes more of a trough, or suppression, of the jet stream along the west coast and the western states, which resulted in above normal rain/snow in that part of the country.
For us here on the east coast, El Nino can cause the jet stream to move farther north into Canada. This put us on the warmer, southern side of the jet stream, causing HIGH PRESHA off the east coast (known as the Bermuda high pressure) to be stronger, and allowed it to push the jet stream farther north.
This gave us milder than normal weather in December, which continued into January.
The exception was the brief very cold weather we had at Valentine’s Day. Now that spring is here, we have seen a change in the upper air pattern, which is different than the one I just stated for this past winter.
This new weather pattern features an Omega Block. An Omega Block occurs when the upper level winds (jet stream) makes the Greek Symbol Omega.
When this occurs, it can be just like a traffic jam on the highway. Weather systems at the surface near ground level stop moving because there is a block of air in the upper atmosphere, which causes surface weather features to stall.
This block can cause a few, to several days of cool damp and wet weather if a given location is not under the upper level HIGH PRESHA system associated with this block.
This is the case for us as we begin the month of May. Until the block weakens and breaks down, our cool, damp, wet weather will not change. Eventually, this air block will break down and we will see a return to warmer weather. However, this can be a slow process. These air blocks can form in the spring months as we are in a transition from winter moving toward summer.
We need patience until the block breaks down. One good features of this block is that the cool, wet weather has cut down the high fire danger that we had.
The recent fire danger was enhanced by the lack of snow we had this year.
Another weather feature we see in the spring is the sea breeze. This can make it quite chilly during the day, especially along the coast. Remember the ocean warms more slowly than the land during the spring. One reason is mixing. The ocean is always moving and this causes more heat from the sun to warm the ocean versus the land areas in the spring. Another reason is evaporation. This is constantly occurring over the ocean. Evaporation is a process where heat is removed from the air and results as a cooling process.
If on a given day the sea breeze is strong, then the chilly air off the ocean can penetrate a good distance inland.
Also, I would like to mention that from early to mid-May we can still get some chilly weather at night. So use caution if planting your garden or leaving plants outside. By Memorial Day weekend it is pretty safe to start planting and leave sensitive flowers outside.
Next month we will talk about hurricane season, which begins on June 1st. Also, we will start to talk about thunderstorms, which will start to increase as we get closer to summer.