Ask the Weather Team
Troy from Metrowest asks: Drought and Leaves Turning.
Jeremy Reiner says:Hi Troy-It sure is....many of the trees around where I live are also changing and dropping!....I used to work in Charlotte, NC and about 10 years ago we had a drought that caused the trees to change color and even drop in mid August---much like we are seeing here.An amazing turn-around compared to the wet summer we had last year.Thanks for watching 7news!-Jeremy
Steven asks: What is a microburst, and how do they form?
Pete Bouchard says: Downbursts, or downward moving winds that rush out of the bottom of a thunderstorm, can be classified as microbursts or macrobursts depending on areal extent of the damage they cause.
All thunderstorms operate like a vacuum cleaner. There's and inlet and an exhaust. The air flowing in sucks up moisture and feeds the storm throughout its life cycle. As the storm matures, it drops rain. This rain cools the air it's falling through, causing it to drop toward the ground (think back to the "warm air rises, cool air sinks" theory). This downward flowing air is the exhaust or downburst. (It's also what gives that refreshingly cool feel during the storm.) Sometimes these winds can reach speeds equivalent to that of hurricanes or tornadoes. The strongest downbursts in recent memory have been clocked at 175 mph at Morehead City, NC! Locally, we've seen downbursts reach speeds of 104 mph in both Worcester on May 31, 1998 and Whitman on May 21, 1996!!
If the damage area extends 2.5 miles or less, it's a microburst. If it's 2.5 miles or more, it's a macroburst. We had a macroburst from a thunderstorm on Sunday June 6th, that traveled all the way from Framingham to Revere.
Andrew asks: What is the name of the clouds that are huge in mass and have a big cotton ball look to them?
Jeremy Reiner says: Hi Andrew-
Those big ol cotton ball type clouds are known as cumulus clouds. There are many types of cumulus clouds....cumulus fractus (small little cotton balls) to cumulus congestus (much bigger cotton balls). They are driven by the energy of the warm sun so they are most often spotted in spring, summer and early fall.
Alice asks: What is the difference between the humidity and the dew point?
Pete Bouchard says: This is a tough one to understand, and one that took me a while to grasp back in college.
Humidity is broken into two types: absolute humidity and relative humidity. Both are designated with percentages. Absolute humidity is the actual water vapor in a given volume of air. Sounds simple enough. Relative humidity, however, is the amount of water vapor in the air RELATIVE to the amount it can hold. This is where it gets complicated.
The key here is you have to know your airmasses. Cold air holds less water vapor than warm air. So let's say you have a glass of water. If you (hypothetically) threw that into a room of cold air, the air would saturate and a cloud could possibly form. But if you threw that into a warm room, the air's capacity is greater, and wouldn't saturate - no cloud. Admittedly, this is a poor way to designate how humid the air is, since you could have a relative humidity of say, 45% in both the dead of winter and the hottest day of summer.
Enter the dewpoint, which is more closely related to the absolute humidity. The higher the number, the more humid the air. The lower the number, the drier the air. The dewpoint also has other applications. Since the temperature NEVER goes below the dewpoint, it's sometimes used to gauge the low temperatures for the night. In its simplest form, the dewpoint is the temperature that the air must cool to reach saturation.
Hope that makes sense!
Cindy asks: What timeframe does the first morning low on the 7Day represent?
That's a great question! In the morning, the first low on the 7Day that I show represents the night before. So if it's Monday, the first low temperature on the graphic is that Monday morning's low. During the evening, the first low of the 7Day on a Monday would be the upcoming night's low temperature (lows usually occur around 5-7am.)