Ask the Weather Team
Andree asks: Can it ever be too cold to snow?
Pete Bouchard says: Technically, no. Every airmass has a temperature and dewpoint, no matter how cold. If you cool the airmass down to the dewpoint, you have saturation and water vapor/ice crystals can form. Get enough moisture particles, and you can have precipitation.
Sometimes in cold climates, the temperatures will cool near the dewpoint and you can have miniscule snow crystals form. They're called diamond dust and they can happen with clear skies. While uncommon at our latitude, they are VERY common in Antarctica. Out of the 365 days in 1970, researchers found that 317 of them had diamond dust.
Victoria asks: In years past, how long into winter did we go without plowable snow?
Pete Bouchard says: Good question. And after the Halloween storm, we felt this might be our winter again, but both November and December have proved that wrong.
After a bit of research with other meteorologists at the National Weather Service in Taunton, we found the following:
Latest 2" snow was on Feb. 16, 1980
Latest 4" snow was on Mar. 3, 1915
Latest 6" snowstorm was on April 1, 1997. Which was also the date for the MONSTER nor'easter that clobbered us with snow over 22" of snow in Boston.
6th Grade UP Academy from South Boston asks: Why was it so warm in early October, and why was the sky so blue?
Pete Bouchard says: This has to do with a phenomenon we call subsidence.
There was a gigantic high pressure system "stacked" 30-45,000 feet up in the atmosphere. This high parked itself over the Northeast and Southeast Canada for a few days last Columbus Day weekend. In meteorology, high pressure systems are defined by their subsiding, or sinking, air. When air sinks, or drops from several thousand feet to the ground, it warms and spreads out in a clockwise direction around the center of the high.
This sinking, warming air provided the basis for our summerlike warmup, and the sun did the rest.
Subsidence also promotes clear skies. The more air you have moving downward, the less likely it is for clouds to form, since cloud formation requires rising air. That's why the skies were so blue and clear on the weekend of the 8th, 9th and part of the 10th.
Ross asks: Why is the heaviest precipitation to the west and strongest wind to the east of a storm track?
Pete Bouchard says: If you're talking tropical systems, this is almost always the case due to the fact that maximum sustained winds are added to the forward speed of a storm. In the case of Irene, the northward movement through New York City and into Vermont placed the strongest winds were over Central and Eastern Massachusetts. To get an idea what we're talking about, look at the image below from the Hurricane of '38. The maximum sustained winds from the storm were 115 mph. Adding the forward speed of the storm (an unheard of - and never before seen - 70mph) to 115 mph gives you maximum winds of 185 mph. To the west, however, the forward speed is subtracted from the maximum winds, yielding wind speeds of 45 mph - a staggering difference!
In addition, tropical systems are undergoing a transition to a more nor'easter-like storm when they move into our higher latitudes, pushing the heaviest rain to the west of the track. There are several dynamic processes going on too that aid in this transformation.
If you're talking about run-of-the-mill storms like nor'easters, this is sometimes the case, depending on track. Due to decrease in friction (no trees, buildings or mountains), wind speed over water is 10-15 mph faster than that over land. This contributes to the coastal flooding, beach erosion, large waves, and, of course, higher winds along the coast.
Rainfall is greater over the hills and mountains due to what is known as orographic uplift. Mountains force air to rise higher, squeezing out more moisture - and subsequently more precipitation. This affect is shown below, and is one of the major reasons points north and west of I-495, in the higher terrain, get more rain (and snow) during a nor'easter.
It goes without saying that the higher the mountains, the heavier precipitation. Note in the image that in higher mountain ranges (like those in Northern New England) there can be a "rain shadow" affect, where very little precipitation falls in the lee of the mountain range. This is one of the reasons places in Northern New England can get a foot of snow in one spot, and only a few miles away get close to nothing in another.
Kathy asks: Is it possible for a tornado to touch down in the Cambridge/Boston area?
Pete Bouchard says: It is entirely possible! Tornadoes can happen ANYWHERE, and just because we're in a city, it doesn't mean we're in the clear. Fact is, tornadoes can and do strike in cities. Oklahoma City, Miami and even New York have had tornadoes touch down within city limits. Although we're not in Tornado Alley, we have had several tornadoes touch down in the metro area since 1950:
