CLOUDY, COOL, DAMP WEEKEND
It won’t be raining the whole time, but there WILL be some rain this weekend, and it will NOT be warm-or even mild. Overall, it looks like Saturday will have better weather than Sunday, but even Saturday is no picnic. It is likely to be raining during the Blue Cross Broad Street Run Sunday morning.
WHY ARE CLOUDS & RAIN SO PERSISTENT?
It’s largely about the wind-specifically the wind direction. The first step in making my weather forecast is always the wind, since it’s so important in forecasting in this area. A wind from the ocean (East or Northeast) will be a major factor, especially if it lasts for days. Eventually, clouds will be moving in, and once they’re here, it’s hard to get rid of them until the wind direction changes. That is the current issue.
Here’s a map of where our air is coming from. New Jersey and Long Island stick out pretty clearly, so you can tell where we are on the map. You can find an animation of this map here:
Computer models show that this basic pattern will last for several more days. This means cooler than normal weather, lots of clouds, and some periods of rain. These persistent East winds are common this time of year, and can keep temperatures in the 50s for days. And if the ocean is cold enough, it can stay in the 40s!
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That’s the current picture. Let’s see how it changes over the next few days…
MORE EAST WIND=MORE CHILLY, WET WEATHER
Here’s a forecast wind map for Friday afternoon. The east wind is coming from hundreds of miles out in the ocean. There’s no way we can warm up with a wind like that.
There’s no sense showing what this map will look like over the weekend, since it will barely change.
Here is the result of those persistent east winds:
That’s the forecast from the NAM model for the same time as the earlier wind map. The green is the rain. That area of rain moves out, so Saturday is merely cloudy and chilly:
But the rain-even heavier rain-is approaching from the west by late Saturday. That means rain for Sunday, and it could be briefly heavy:
It doesn’t improve for Monday. But that should be the last day of the east wind-aided chill and rain. We’ll get back to normal-eventually.
Here is the forecast for the next 4 days:
Friday: Cloudy and chilly. High only 55. Periods of rain, mainly in afternoon
Saturday: Cloudy and chilly. High 61. Chance of rain at night
Sunday: Rain, heavy at times. Still chilly, with high only 58.
Monday: Periods of rain. Still chilly, with high 61.