The monsoon has officially arrived in Arizona. KNAU's Gillian Ferris spoke with meteorologist Lee Born about the start of the summer rains.
GF: The monsoon was right on time, it actually rained in Flagstaff on the first day of the monsoon. Is that unusual or typical?
LB: It is pretty unusual. Well, now we're in this new definition of the monsoon where it starts June 15th. So, it began on Sunday and we did get that little surge of moisture and we saw a few rain showers out there on Sunday right on cue with the first day of the monsoon which is pretty unusual. That's an early rain here in June, still a bit early for us to be seeing some rain showers.
GF: So when you say 'the new monsoon system', can you explain that to listeners?
LB: In 2008, The National Weather Service made the monsoon - the North American monsoon, the Arizona monsoon - run from June 15th to September 30th. And this was done in order to place a greater emphasis on monsoon safety and thunderstorms and eliminate confusion with people who are like, 'is this the monsoon or not the monsoon?'. You know, we used to track by dewpoints but now it is just a set season with those dates. Similar to the hurricane season; there doesn't have to be a hurricane for it to be hurricane season. And there doesn't have to be thunderstorms for it to be the monsoon season.
GF: So as long as we're talking about definitions, you brought up dewpoint, and I know that's a way that the monsoon is tracked. What is the dewpoint, exactly?
LB: Dewpoint is a temperature, and it's a good indicator of how much moisture is in the atmosphere. The greater the dewpoint, the more moisture there is in the atmosphere. And what it is technically is that is the temperature you need to cool the atmosphere down to in order to saturate it. Our dewpoints right now are in the low 20's, upper 20's. You need to see dewpoint temperatures to raise into the 40's at least here in Flagstaff to start seeing some thunderstorm development, although we did get those weak ones with some dewpoints in the 30's. But, when we start to see our dewpoint temperatures creep up into the 40's, that's a good indicator that the real monsoon moisture surge is moving into the state.
GF: So, what was the old way of tracking the dewpoint, then?
LB: The National Weather Service here in Arizona...the way we used to track the monsoon, and we still do it for climatological purposes because that's the way when we really know the moisture's here. But, when the moisture arrives from the Gulf of Mexico, our dewpoints jump up into the 40's and 50's. And the old definition of when the monsoon was officially here was 3 consecutive days of an average dewpoint temperature at Sky Harbor Airport of 55 degrees. And when that happened, Phoenix would say 'the monsoon is here' and we would suit, usually, with Phoenix on 3 consecutive days of 55 degree dewpoint. And that's when it starts to get muggy around here and you really know that we're in the season.
GF: We had some very high temperatures last week. Flagstaff was in the 90's a few days last week, and that seems pretty hot for early June. Did we set any records last week?
LB: As a matter of fact, we did. We had two 90+ degree days, I think we hit 91 one day, maybe 92. And 90 the other day, and those were both record high temperatures for that particular day. We average 7 days here in Flagstaff of 90+degree temperatures (a year). But, many years we don't even ever hit 90. Last summer, last calendar year 2012, never even hit the 90 degree mark which I just love about this town. And this year, hopefully, our 92 degree day is our hottest day. Hopefully, we just got that out of the way. But, you've gotta love a heat wave in Flagstaff...can't complain too much about the low 90's.
GF: Lee, you sent out a great email last week explaining the correct grammar to use when talking about the monsoon. Could you share that grammar lesson with our listeners. As a writer I thought it was interesting.
LB: Well, monsoon is a season, it's always meant to be thought of as a season. So, it is incorrect to ever use it plural like, 'the monsoons were really strong today'. It's always a singular word like, 'the monsoon is about to hit'. We;re not waiting for the 'monsoons' to roll in. They're not a thing, it's a season.
GF: Is that a super-pet peeve for you?
LB: Um, it bothers me, particularly if someone in the media is using it, it's even worse than my friend on the street.
GF: Ok, now I'm watching myself carefully on that one.