Weather Banter - Mexican monsoon - "the least understood weather event in North America"

U.S.-Mexican team going all out to find secrets of unusual weather
By Thomas Stauffer
ARIZONA DAILY STAR (6/27/04)

This upcoming season may go down in history as the year meteorologists
finally began to figure out the Mexican monsoon, the least understood
weather event in North America.

A fleet of more than 90 weather stations in the United States and Mexico,
two weather ships, a weather plane, and a huge platoon of weather balloons
are already at work as part of a landmark project to study the monsoon and
better predict its moves.

Forecasters say this year's monsoon, which has been very generous to parts
of Mexico, will probably arrive later than the average date of July 3.

But no matter how much equipment and how many scientists you throw at the
phenomenon, some questions may never be answered, said meteorologist Erik
Pytlak of the National Weather Service.

"When it comes down to things like, 'Am I going to get rain at my house
today?' that's the kind of thing we'll probably never be able to tell you,"
said Pytlak, who will serve as rotational leader for the 2004 Field Campaign
of the North American Monsoon Experiment. "But there are some very important
aspects of the monsoon that we do think we'll understand much better after
this."

For those who favor local lore over local science, the monsoon should be a
good one, according to superstition.

If the summer rains arrive before June 24 - the feast day of San Juan - it
portends a stingy monsoon, but if the season waits until after the feast
day, we get plentiful rains, Tucson folklorist Jim Griffith said. If the
season actually starts on the 24th - which it didn't - that's "an even
better sign," Griffith said.

Tucson gets an average of 6.06 inches of monsoon rain, a little less than
half the annual average total of 12.17 inches.

Meteorologists have a pretty good handle on U.S. weather phenomena - from
hurricanes to tornadoes - with the major exception of the monsoon, Pytlak
said.

"It really is the least understood weather event in North America," he said.

Pytlak said the big payoff from the joint U.S.-Mexican experiment, which
will gather data from more than 20 types of instruments at more than 100
locations, will be better forecasts in the short, medium and long terms.

"The big thing from our end is that we'll be able to forecast these storms a
little more accurately hours in advance," he said. "But the benefits also go
weeks and months in advance. For example, the big question in June is 'When
is the monsoon going to start?' and that's not only helpful to the public
but also for people doing things like fighting wildfires."

Further out on the time scale, forecasters will be able to better predict
how an entire monsoon will shape up, said Wayne Higgins, lead scientist for
the experiment.

That kind of longer-range forecast will be a big help to people who allocate
water resources and grazing rights, Higgins said.

Pytlak said the program may also answer another longstanding questions: Is
there a better way to officially herald the season's arrival other than the
dew-point criteria now used?

The dew-point system is a holdover from the days when the only National
Weather Service office in Arizona was a hundred miles to the north,
meteorologist Jeff Davis said.

"Phoenix, they're the ones that started this whole dew-point thing, and
they've done it for years," Davis said.

Dew point is the temperature that a sample of air has if it's cooled until
dew, or frost, begins to form on a surface next to it. When the average
daily dew point was 55 degrees or above for three days in a row in Phoenix,
the office there reverted to the first of those three days and officially
declared the monsoon's arrival for the entire state.

Until the mid '90s, Phoenix called all the weather shots for Arizona.

"That didn't really serve people in Tucson, because the monsoon almost
always hit us earlier by a few days."

When Tucson spun off its own weather station, it kept the dew-point
criteria, but lowered the temperature a degree to compensate for Tucson's
higher elevation.

Pytlak said he wishes forecasters had thrown out the system altogether.

"It's this thing that was used 50 years ago when they didn't have satellites
or Doppler radar and other resources, and it's really not a very good
indicator," he said. "Maybe this experiment will show us something better to
use, but whatever it is, it's got to be readily identifiable to the public."

A good example of the fallibility of the dew-point criteria came in 2000,
when Tropical Storm Bud moved into Southern Arizona, raising the dew point
past 54 the required three days, meteorologist John Glueck said.

"It met the criteria on June 17, but it wasn't really the true, classic
definition of the monsoon," Glueck said.

The public is all that really matters when it comes to getting technical
about the start of the monsoon, as most meteorologists see it as nitpicking,
Davis said.

"Really, preferably, we would just call it our summer thunderstorm season,"
he said. "We're really on the northern fringe of the Mexican monsoon, and
Arizona is really the only place with a criterion for trying to declare the
start of it."

Neither Mexico nor New Mexico bothers with the technicality, Davis said.

"They don't really care, and they get more thunderstorm activity throughout
the season than we do," he said.

Tucson meteorologists now count any precipitation that falls from June 15
through Sept. 30 as monsoon rainfall, regardless of what the dew-point
criteria reveal.

"The rain that some places got this week, that wasn't technically monsoon
rain, but it was associated with the monsoon," Pytlak said last week.

Though our monsoon pales in the amount of precipitation it delivers when
compared with the Asian version, it's still very much a monsoon. By
definition, a monsoon is a seasonal shift in wind direction, and that's very
much what happens, Davis said.

By the way, monsoon means the season, not an individual storm.

"Each individual storm is not a monsoon. Don't do that. That's a big bugaboo
with me," Glueck said. "On the radio, sometimes you'll hear them say, 'We're
going to have more monsoons today,' and that just drives me up the wall."

? Contact reporter Thomas Stauffer at 573-4197 or at .

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