July 11, 2008

Monsoons in Santa Fe

After having to leave the therapy pool early this evening
due to a lightning storm,
I checked New Mexico monsoon information:




(Image from: www.abqjournal.com/pix/1lightning03-31-08.jpg)


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Rain: Counting on the monsoon season

This article appeared in the Summer, 1997 issue
of New Mexico Resources.


Ask meteorologists to describe New Mexico's weather
and they'll you it has a semiarid, subtropical climate
with abundant sunshine, gusty winds,
little rainfall, and low humidity.

Ask farmers and ranchers to describe the weather,
and they tell you about droughts that parched range grasses
and dryland crops, hailstorms that flattened a promising year,
rains that ruined cut alfalfa, frosts that zapped fruit,
winds that sandblasted vegetables, and cold snaps
that killed sheep and cattle.
Their highest compliment about the weather is, "It wasn't bad."

Whether you see it in scientific terms
or watch its effects on a particular crop,
New Mexico's weather is variable and extreme.
National Weather Service (NWS) records show temperature extremes
ranging from -50 to 122 degrees.
In a single day, temperature swings
of 30 to 40 degrees are commonplace.

Many southern New Mexican towns claim
up to 350 sunny days each year,
although Max Blood, meteorologist-in-charge
with the NWS monitoring station in Santa Teresa,
can't remember a call for sunshine statistics in eight years.

Though rain is scant, New Mexico has more than its share
of severe weather, including thunderstorms, flash floods, hail,
lightning strikes, high winds, and tornadoes.
Annual snowfall can vary
from less than two inches in southern deserts
to hundreds of inches on northern mountain peaks.

Wind is a powerful force in New Mexico,
not only for pumping water but also for shaping the weather.
One somewhat predictable event in New Mexico's weather
is "monsoon season" in July and August,
when most of the rain falls in summer thunderstorms.
Though it may seem a stretch to talk about
a monsoon in the desert,
the term actually has more to do with wind than rain, Blood says.
"When you grow up, in school you learn about the monsoon season
when they have tremendous rains in India," he says.
"But monsoon does not refer to rain per se,
but to the reversal of flow that brings an increase in moisture."

When the wind changes direction during monsoon season,
it sets up a southerly flow of moist air,
which condenses over land and falls as rain.
In New Mexico's case, the monsoonal flow pulls up moist air
from the Pacific Ocean and Gulf of Mexico,
triggering summer thunderstorms.

No matter how much rain a storm brings,
it won't erase the ever-present threat of a drought.

Though it's no laughing matter,
the punch line to Extension farm management specialist
Jim Libbin's favorite weather joke makes the point:
What did the New Mexican say on the first dry day
after 40 straight days of rain? "We're heading into a drought."

This century, droughts have parched the state
in the early 1900s, 1930s, 1950s, 1970s, and 1990s.
For New Mexicans who have felt the effects of drought firsthand,
it's no comfort to hear that the last 200 years may have been
the wettest period in 1,500 years.
Researchers with California State University
drew that conclusion after examining 2,000 years
of tree ring evidence from New Mexico.

Whatever the case, John Fowler,
coordinator of NMSU's Range Improvement Task Force,
still remembers the best drought advice he heard
from an old-timer nearly 20 years ago.
"He told me that unless you're born in the Southwest,
you can't ranch here because you don't understand
the power of drought," Fowler recalls.
"To survive, New Mexico ranchers have to
manage as if every year will be a drought.
You bet on drought, you use low to moderate stocking rates,
and you have financial reserves if you're in it for the long run."

Even after the rains come, it may take years for ranchers
to recover financially and to rehabilitate rangeland.
In a drought, perennial grasses lose ground to annuals,
shrubs encroach, and noxious weeds gain a toehold, Fowler says.

For dryland farmers who try to coax a crop
from areas with marginal rainfall,
four straight years of dry weather are disastrous.
For farmers who must pump water from wells
to keep crops alive, energy costs may be prohibitive.

Just as important as how much rain comes
is when and how it falls. Averaging covers up many extremes.
The first half of the year may be one of the driest ever,
only to be followed by record-setting rainfall in the last half.
Several inches can fall in a four-hour flash flood
or dribble out in quarter-inch showers throughout the month.

Farmers with surface water allotments
generally prefer the predictability of scheduling their irrigation.

"Dryland farmers in eastern New Mexico want rain but not hail,"
Sammis says. "Growers who irrigate don't necessarily want rain.
They want control. Vegetable people, like lettuce growers,
don't want rain because it can damage their crops."

Though it won't ever set records for total rainfall,
New Mexico has the highest number
of lightning injuries and fatalities per capita.

The reason is that in wetter climates,
rain drives people indoors,
where they're protected from lightning,
says Hayes, the warning coordination meteorologist.

"What happens here is that people feel a few raindrops,
but they don't stop the little league game
or the round of golf or the hike along the top of the ridge,"
he says. "That's why more people get hurt."
Dry lightning storms, in which rain evaporates
without ever reaching the ground,
can start devastating range and forest fires.


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Oh, and it is still raining,
(with lightning & thunder),
2-1/2 hours later...

Have a great weekend!
M

1 comment:

l/elle said...

Wow. I think you just became a weather geek.

I recommend the weather wardens sci-fi series by Rachel Caine for a completely different look at the forces that drive our weather . . .

L