Ask the Weather Team
Joe asks: How do you measure snowfall accurately?
Pete Bouchard says:
In the 'old days' weather spotters had a snow board that was wiped clean after about three hours (could go four, but no more than that). Each three hour period was added up for a storm total accumulation. This eliminated the settling that can occur when several inches pile up on the ground.
Nowadays, very few use the snowboard for measurements. They are typically taken at the end of a storm by taking an average depth in an area where there is minimal drifting. If the area is in a windy location, spotters use their best judgement and try to average the depth of the accumulating snow. Places like TF Green Airport are notoriously difficult to get accurate readings because of drifting. In our past storm, they recorded "only" 18" of snow.
Dennis asks: After the solstice, why do we gain daylight during the sunset, but still lose it at sunrise?
Pete Bouchard says: First off, you have to calibrate your mind to reject the idea of clock time and embrace the idea of solar time.
Each day, the sun reaches its highest point in the sky, what we deem the solar noon.
Like it's name implies, the solar noon usually happens around noontime. The time it takes for the sun to go from one solar noon to another is called the solar day. Most times the solar day is 24hours, however, during the solstices (winter and summer) the solar day is a little more than 24hours. Since the solar day is longer, the solar noon is a little later.
Have I lost you yet? Good. Now let's take it a step further.
From Larry Denenberg, a Newton resident with an exhaustive review of the subject online:
Now the time from solar noon to sunset doesn't change very much near the winter solstice. Therefore, since solar noon is a little later each day, sunset is also a little later each day. But if sunset is a little later each day, then the earliest sunset has already happened! Similarly, later solar noons at the solstice imply later sunrises, hence sunrise is getting later and the latest sunrise is yet to occur.
Now I've lost you, huh? Well, the reason for all of the above is simply this: Earth's axis it tilted with respect to the sun, and our orbit around the sun is more of an ellipse than a perfect circle.
I should have started there.
Drew asks: When is the warmest part of the day? Coolest
Pete Bouchard says: Complex explanation to a simple question, Drew. In essence, it depends on the season.
Typically in summer, our warmest time of day is 3-5pm in the afternoon:
In spring and fall, the warmest part of the day is typically 1-3pm, in winter- it's around noon.
The reason is that the sun's energy, while maxing out around noon, is still heating the surface throughout the afternoon. In addition, the surface continues to radiate that energy as well. The lag time between the sun's peak and the warmest afternoon temps is around 3-5 hours, which is when we see our high temperature. In the spring/fall the days are shorter, so the lag is shorter too. In winter, there is very little heating from the sun at our latitude, so on a sunny day with light wind, our warmest temps coincide with the noontime hour.
Soil composition and vegetation can also affect temperatures. If the soil/vegetation is a poor radiator, then the lag time can be shorter. If it's a good radiator/absorber, it can push the high temperature later into the afternoon.
Coolest part of the day is right at sunrise on almost every morning – no matter the season. At the moment of sunrise, the sun’s energy evaporates the small (or sometimes large) amount of water vapor (ice crystals in winter) in the air. Evaporation is a cooling process, which results in a drop in temperature at the moment of sunrise.
John asks: Why has it been so humid this summer?
Pete Bouchard says:
The answer is twofold:
1) There haven't been many dry, cool Canadian airmasses invading New England this summer to bring us relief
2) Water temps have been abnormally warm off the coast of New England, harboring the sticky air and sending it ashore with every afternoon sea breeze.
Thankfully, that trend has reversed this week. I do believe we've turned the corner, and the hottest, most humid days are behind us.
Stephen asks: Why is fog so common this time of year at the beaches?
Pete Bouchard says:
The simple answer is that the fog is caused by the warm air sitting over the cold ocean. But it isn't just any warm air - we've had days in the 80s with crystal clear blue sky over the ocean - the air has to have some humidity (or moisture) to it. When that warm, moist air is pushed out over the cold ocean, the moisture condenses and a fog bank forms. The term we use for this is Advection Fog.
It's common in the spring and summer (but can and does happen year around) because the warm air and cold ocean temperatures are constantly clashing. And while it may seem bright and beautiful when you leave the house, it can really skunk a day at the beach.