Memorial Day Weekend Shows Improving Forecast

I asked my smartphone this morning what the weather was like for the weekend. It told me there was a chance of showers and then showed me this picture.


I had to take a picture of the image with my camera to show you. If you don’t have a smartphone and instead Googled the weather, I suspect you might see something quite similar.

I really dislike icon forecasting. Unless it’s a snowy, rainy, completely sunny or cloudy day it’s a bad way to understand the weather. The icons rarely tell you the whole story. Even if you look at the hour-by-hour forecast, you would still see rain for much of the weekend and this isn’t going to be the case.

I’ll be updating the forecast @growingwisdom on Twitter.

Our chance of rain comes from a weather system located high in the atmosphere. It’s more of a disturbance which will help to bring lift to the atmosphere. This will allow the air at the ground to rise and form showers. While this is the case, we also have cool marine air along the coastline. This cool air acts to push the air back the ground and deflates the showers. Put another way, as the showers move eastward today and tomorrow they are going to fall apart.
Let’s look at a few maps to understand the weekend forecast. The first is the probability of rainfall. Remember, these maps are based on the models and won’t be exactly right. However, they do give a good idea of trend and pattern. Notice the chance of rain today is greatest west of Route 495. Most folks out in Springfield can expect to get wet today. However, see how the chance of rain tails off to around 30% in Boston. This means there is a 70% chance we won’t see any measurable rain today. The map would look very similar for tomorrow. The next map, for Sunday, shows the probability drops to around 20%. At these levels, I could remove showers from the forecast entirely, but for the one or two towns that see a quick shower I leave it in. By Monday the chance is virtually zero and that is our nicest day of the weekend.

probability fri.jpg

probability sun south.jpg

The other part of the rain equation is how much rain is going to fall. If we get 2 inches of rain it’s a very different proposition than two tenths of an inch. From today through Sunday we are looking at very little rainfall over eastern Massachusetts. The map below estimates how much rainfall will occur through Saturday at 8PM. Notice Boston has around a tenth of an inch while the Cape and Islands have even less. If you are headed west, you can expect more in the way of significant rainfall. This is all related to that marine air keeping the heavier showers away from the coastal plain.

rain sat south.jpg

The weather map for Sunday shows the rainfall positioned over the Connecticut River Valley with basically no rain along the coast. Temperatures in this pattern will be coolest at the water and warm as you move west away from the ocean. The next three maps show high temperatures over the weekend. Notice by Monday it will be warm enough to perhaps even go for your first swim although the lakes and ocean water is still very cold.

SUnday sfc map.jpg

Tides will be high between roughly 8 and 10 AM this weekend and low between 1 and 3 PM. Check your local tide chart for each specific area. The sun is up just after 5 AM and down just after 8PM for some of the longest amount of daylight of the entire year.
The bottom line on the weekend is there’s a chance of showers tomorrow, but by Sunday and Monday the chance diminishes towards zero. Sunshine will be less abundant Saturday and then increases each day through Monday. It’s coolest, only in the lower and mid 60s Saturday and warms into the 70s to near 80F by Monday. Have a great weekend whatever you do.

highs sat south .jpg

highs sun south.jpg

Highs Mon south2.jpg

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