Donít be fooled by the great morning of sunshine and a comfortable temperature, the atmosphere is ready to grow some thunderstorms today. Itís going to be dry this morning at least into the 11AM hour, but beyond that clouds will have grown big enough to start the thunderstorm action.
The storms are most likely around Boston between noon and 4 pm, but earlier west and later over Cape Cod. Once the sun sets, the storms will quickly fall apart and leave us with a clear and comfortable night. The next 5 nights are going to bring some of the best sleeping weather you could hope for in early to mid August. Some of the colder spots will see readings in the upper 40s tomorrow morning. This probably isnít what some of you want to hear because itís going to feel more like September around 6AM. However, my unscientific twitter survey found significantly more of us love these cool mornings.
The sun is still quite strong this time of year and although we have lost an hour of daylight, afternoon readings are going to be warm. We should enjoy highs around the 80 degree mark the next several days with readings slightly cooler along the coastline.
After todayís storms, the next opportunity for rain wonít come until sometime in the Tuesday or Wednesday time period.
There are several reasons for the chance of storms this afternoon. Not all of us are going to see them, but 7 out of every 10 cities and towns in the area will. There is enough moisture in the lower levels of the atmosphere to produce storms this afternoon. We also have the strong August sun to aid in warming the air at the ground and lifting it into the atmosphere like a hot air balloon. The other piece of the puzzle and why hail is part of the forecast is the unusually cold air above us today.
This morning was nice and cool here at the ground, but up at 10,000 feet and higher itís below freezing! This is quite unusual for early August. If you are driving or climbing Mount Washington in the next few days, itís going to be quite chilly by the time you reach the summit. The temperatures this morning are around 40F and there is a wind chill of 28F!
Meteorology 101-Unstable air
When you have cold air above and warm air below in the atmospheric profile it creates what is called an unstable sounding or simply put, thunderstorms are more likely to develop. The chart below shows what the atmosphere looked like just before sunrise. I put a red box around the level where temperatures are nearing zeroį Fahrenheit which is -18į Celsius. The two numbers you see are Temperature/Dew Point Temperature. The greater the difference the drier the air is. Notice around 5000 feet high, there isnít much of a difference between the two numbers, this layer of the atmosphere is moist and is that is going to help build the clouds quite quickly.
Better weather begins tomorrow
Once we get by the showers today, the weather looks stunning for several days. I know many summer rentals are Saturday to Saturday and the upcoming rental period should feature some fantastic days. For your planning purposes, next Wednesday looks like the least favorable day for the beach, more on that in the days ahead. This can of course change.
Iíll be updating the forecast @growingwisdom on Twitter.