Ask the Weather Team
Dave asks: Why does Norwood always seem to be the coldest spot on the temp. maps?
Pete Bouchard says: The temperature is taken at the Norwood airport, which is in a relatively low spot compared to the surrounding terrain. It is also in the shadow of the Blue Hills. Both of those topographic facts mean that the cold air likes to "puddle" there, creating much colder readings than in nearby towns and cities - so much so, it "throws" the temperature range in our nightly forecast!
Chris asks: What is the Greenland Block and how does it affect us if we're so far away?
Pete Bouchard says: There's been a lot of talk about this block over Greenland both in this winter and last. It's been responsible for hammering the Mid Atlantic with snow last year, and producing our near-blizzard this Christmas.
Best way to describe it is to use an analogy. Think of a big boulder in a a stream. Water is diverted around the boulder and eddies are formed. Same goes for the high altitude "river of air" that steers our storm systems. If there's a high pressure system that won't budge in the jetstream, the storms are diverted around it.
When this high pressure system (or block) over Greenland is situated just right, we are at a junction point for storms. They form, slow down, and are redirected right near us. We can get whacked by snow (or rain if the weather is warm enough) for a couple of days before the storm finds a way around the block.
Typically these blocks last for several weeks when they set up, depending on their strength and size. Over the last decade, they have at times been gargantuan - logjamming weather systems as far back as the Great Lakes. Meteorologists from Environment Canada have theorized that the reason these blocks are large and persistent is because the Arctic Ocean is melting and a cause and effect feedback has been established between warmer ocean temperatures and upper atmospheric high pressure. Whether or not that is a major part of the puzzle of climate change is still being debated, but one thing's for sure: we've got to start boning up on the forecasts for Greenland.
Where's YOUR winter forecast?
Pete Bouchard says: Although many other meteorologists like to give their impression of the winter forecast, I don't. From what I've seen, there's no proven science to a seasonal forecast whatsoever. Although many people like to hang their hats on what El Nino or La Nina may or may not do to New England, the fact of the matter is the signal from either is weak here in New England, and we've had winters (and springs) that are both warm (rainy) and cold (snowy). El Nino & La Nina are variations in the Southern (Pacific) Oscillation. Our winter weather mostly depends on the North Atlantic Oscillation. So far, no one has been able to predict with accuracy what that will do in ANY season. So to go out on a limb and predict a seasonal forecast amounts to nothing more than a guess...or in the case for snow-loving meteorologists, "wish"casting.
We all know that recently (within the past decade) all seasons have seen dramatic temperature and precipitation swings. It's nothing to see records shattered - sometimes within a week of each other! I think the bigger question is, why is this happening? Is this the new norm? Ironically, the answer may be more predictable than a seasonal forecast.
Chris from -NA- asks: What makes a storm stall like the blizzard of 1978?
Jeremy Reiner says: Hi Chris-
Great question! Our storms are pushed along by the jet stream and normally that jet stream (or storm track) is like a garden hose stretched out. Sometimes though the jet stream can develop dips (like a garden hose). When this happens, these storm get 'stuck' in one general location for several days. This is what happened during the Blizzard of '78. Here's a picture of a 'blocking' jet stream:
When that pattern happens, typically the east coast of the United States is prone to slow-moving snowstorms....like we saw in the Blizzard of '78 AND like Washington D.C. saw twice last winter.
Hope this helps---thanks for watching 7news
Maeve asks: Why is it that some hailstones are really big, and some are small?
Pete Bouchard says: Hail size is dependant on the updraft - or upwardly moving air - inside a thunderstorm. Simply put, the stronger the wind, the larger the hail. Strong winds moving upward can lift and support larger hailstones than thunderstorms with weaker - or light - winds. Temperatures within the cloud matter too. The lower the freezing level in a cloud, the more likely that it will produce hail. Typically, if the freezing level is below 11,000 feet, thunderstorms are more likely to contain hail.