Well Memorial Day weekend is knocking on the door now and before you know it we’ll be celebrating the 4th. So because the start of meteorological summer (June, July & August) is right around the corner and a lot of you have already begun making plans, I have posted my thoughts on the upcoming summer season in the paragraphs below.
Before I get started I just want you to keep in mind that there are several influencing factors that I have taken into consideration, but in order to keep things simple I will talk only about the main ones that should dominate the weather pattern this summer. So if you read another summer forecast and they mention things that I haven’t (i.e. AMO, PDO, PNA, SOI, the tropics and so on), more than likely I have already looked at those as well. However, those types of weather cycles get a little technical and without visuals I may end up losing some of you as Im explaining it. So I will just keep things simple.
In short I think this summer season will be dominated by the ENSO cycle (La Nina/ El Nino). The winter season was dominated by the mild La Nina (along with other factors) that activated the Southeastern Ridge. The summer season should end up being dominated by it’s counter-part, the cooler El Nino which will activate the desert southwest ridge.
Lets focus our attention on the Pacific Ocean real quick. The Earth is made up of 70% water. Out of that 70%, a large portion of that is the Pacific. So the temperatures of the Pacific, naturally, almost always end up having one of the biggest influences year in and year out on our weather here in the United States.
The ENSO Cycle (El Nino/ La Nina) is a temperature cycle in the equatorial waters of the Pacific Ocean. For reasons still unknown to scientists every 3 to 5 years the waters off of the coast of South America (concentrated near Peru) turn unusually cold. While this is happening the waters on the other side of the Pacific, near Tahiti turn unusually warm and an imbalance develops. This is called the La Nina. The El Nino is actually just the opposite with the unusually warm water off of the coast of South America and the cold water near Tahiti. Well everything interacts because in this wonderful world of weather, t’s all connected. The oceans, the atmosphere, hemispheric wind cycles, even the solar cycle, it’s all connected. So when you change the temperature of a large body of water like this it will end up having huge impacts on the atmosphere and the weather pattern further down the road, in particular the jetstream. The ENSO cycle moves the jetstream (also known as the general storm track) all over the place thus having dramatic effects on our local weather.
This summer the El Nino returns which will activate the desert southwest ridge. This is the high pressure system that is responsible for the oppressive heat in the Four Corners states. While it is smoking hot out there every summer, during an El Nino this feature ends up becoming the main player in the weather pattern. It will tend to shift east from time to time and as it does so the heat will shift east along with it. However, most of the time in an El Nino pattern this high pressure system will end up planting itself right over the Arizona/ New Mexico border. With the jetstream wrapping around to the north, the positioning of this high (in terms of latitude and longitude) usually allows the jetstream to bend southward into the eastern Great Lakes and Mid Atlantic States. The jetstream (storm track) divides the hot air to the south from the cooler, dryer, air to the north. So with the jet frequently diving into the Virginias this summer, that should keep us on the comfortable side of things. If this becomes the dominant weather pattern this summer, and I think it might, that would mean that most of the season should be fairly enjoyable around here.
I think we will end up getting quite a few hot days (90 degrees or higher) this summer, but before an extended heat wave can develop the jet will dip and throw a complex of thunderstorms our way, cooling us off. There will more than likely be some variation in this pattern from time to time, but this should end up being the overall set up.
So my thinking here is ENJOYABLE weather this summer with 10-15 days of 90 degree plus heat. On average Philadelphia usually sees about 18 of those days. So slightly cooler than normal temperatures when the numbers are all tallied up. I think we will see one to two heat waves ( 3 consecutive days of 90 degrees of higher). As far as precipitation goes I think we will end up seeing slightly more rainfall than normal as well. The wild card here however, is the tropics. AccuWeather is forecasting a slower than normal tropical season this year. But as we all know it only takes one of those storms to run up the coast and then you have all kinds of flooding problems to deal with. So assuming we do not see a tropical system this summer I am going with only slightly above normal rainfall.
How This Could Go Wrong
As is the case most of the time with weather, nothing is ever etched in stone. One of the ways this forecast could fail is lag time. Think of it this way, you ever wonder why in April and May you can have air temperatures in the 80s and 90s yet the ocean is still freezing cold!? It’s because of lag time. It takes much longer to warm the ocean than it does the ground because the sun actually heats the ground, not the air, in turn the ground heats the air directly above it. It’s a process called conduction. That’s why you can burn your hand if your holding a pot handle without a holder. The flame didn’t actually burn you, the handle did. Well how did the handle warm? Conduction. The ocean acts differently. Therefore, when you change the temperature of the water it takes time for the effects to be felt throughout the northern hemisphere. So the El Nino is already in the process of developing, now comes the process of lag time. In other words how long will it take for this new pattern to kick in. Assuming it takes about a month (May) then the forecast should play out. If the lag time takes longer than this forecast could bust. We’ll see. For now I like what I have.
So Im thinking that this should end up being an ENJOYABLE summer with our temperatures this year with a few hot days thrown in there from time to time. Then, of course, your typical thunderstorms. I don’t see anything out of the ordinary this year (wild card again being the tropics). So ENJOY!
– Chris –