During the overnight hours a low pressure system passed south of Maine and with it the latest opportunity for some rainfall. Depending on where you live, it’s getting a bit dry, but not excessively so.

One part of southern Maine which has seen adequate rainfall is in the western part of Oxford and Cumberland counties. Some parts of Bridgton for example have seen above average rainfall over the past few weeks. This of course is good for gardens, but bad if you don’t like mosquitoes. The map below shows how much above or below average the area is for rainfall over the past couple of weeks.

Summer Storms
Most of our rainfall this time of year comes in the form of showers and thunderstorms. We can have severe weather, but most storms are not severe, especially at the coast.

When I get to the section on thunderstorms in my college course, one of the more interesting topics is Mesoscale convective systems (MCS) and mesoscale convective complexes (MCC’s). These clusters of organized thunderstorms are where much of the Midwest’s precipitation arises from during the summer.

Last night an MCS like system passed south of us. These blobs of storms can take on several shapes and sizes the exact configuration of which is critical in determining if you are going to get rain or not. Notice some heavy rain fell over southern New England overnight.

What’s An MCS?
Think of these entities as organized clusters of thunderstorms acting together rather than the scattered nature of storms we often see in the summer. On a hot humid day when thunderstorms pop up they only last about an hour and often appear seemingly randomly.

These storms don’t move together, but do generally travel in the flow of the atmosphere, often west to east or north to south in this area. Sometimes, the individual storms will also move southwest to northeast ahead of a cold front or other boundary.
In the MCS and MCC scenario, the storms act as a unit and move west to east or northwest to south east along some boundary. In tonight’s case, the boundary is well defined. The divide between the cooler and drier air over New England and the hot and humid air to the south will provide an ideal breeding ground for an MCS to form.

There isn’t anything unique or unusual about this. I’m just using terminology which typically isn’t shared in the mainstream media. You’ll likely hear about a cluster or storms or an areas of rain, rather than an MCS.

Radar Tells The Story

Within the structure of the MCS you can have a squall line of storms with severe storms and torrential rain. The conceptual radar evolution below shows how these systems form over time. Notice the line of reds and oranges inside the larger blob of precipitation. That is the squall line. As one progresses through the letters the line dissipates and a new line forms. This process can continue for many hours.

If you are really interested in reading and learning more about MCS’s and MCC’s you can click here. I put a link to a lesson on these phenomena there. It’s a fairly advanced explainer about them, but I think you can likely gain more knowledge about them.

This weekend high pressure will build into the area and bring one of the nicer weekends of the summer. Warm readings and humidity which will be typical, but not oppressive for mid-July are two the features in addition to all the sunshine we can enjoy.

If you have a question or comment please tweet me @growingwisdom. Have a great weekend.

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