Summer
thunderstorms normal but indicate changing patterns, weather experts say
By Jessianne Castle EBS ENVIRONMENT & OUTDOORS EDITOR
BIG SKY – Appearing billowy and soft
in the sky, cumulous clouds churn together forming a dark anvil-shaped mass that
blots out the summer sun. They drift ominous over Lone Mountain before
unleashing a force of thunder, lightning, pounding rain and hail.
It’s not unusual for thunderstorms
to crack open summer skies in the mountains, but the omnipresent afternoon squalls
this July across a large portion of southwest Montana have done more than spark
a handful of wildfires—they’ve also got many wondering if 2019 is turning out
to be an unusually wet year.
While a severe thunderstorm can evoke
those feelings of awe and terror in the moment of the storm, weather experts
say this year’s storms are fairly typical of the overall climate in Montana.
According to National Weather
Service meteorologist Joe Lester, who is based in Billings, our thunderstorm
intensity is pretty normal, and while it’s been a wet year, precipitation
hasn’t been off the charts. The Gallatin River Basin, according to the Montana
Snow Survey Program, received 109 percent of the normal precipitation in July.
This amounts to fractions of an inch of more rain.
“I don’t think it’s been anything
too out of the ordinary,” he said, however he added there’s been a change in our weather pattern: As compared
with the past few years, the thunderstorm season seems to be happening later in
the summer, meaning we’re likely to see that hot, dry weather southwest
Montanans are accustomed to later in August.
The reason for the delayed rain
clouds? Lester describes the immediate reason as having to do with the actual
mechanism of a thunderstorm. A wet spring keeps humidity up, allowing
instability to build within the clouds, thus maintaining an almost daily
thunderstorm potential.
There are three ingredients
required to make a thunderstorm: moisture, unstable air and lift.
As the sun heats air near the
ground, cold air blown in over the mountains causes the warm air—which weighs
less than the colder air—to lift. As this air rises rapidly, it creates
turbulence and transfers heat from the earth surface to the upper levels of the
atmosphere. This produces a buildup of water vapor that forms a cloud and as
the outside air cools, water and ice develop.
The turbulence creates an
electrical charge in the storm cloud in the same way as rubbing your feet on carpet.
As the cloud becomes negatively charged, it is attracted to a positive charge
on the ground and the electrical current is discharged, resulting in lightning
and thunder. Lightning, coursing at 50,000 degrees, Lester says, heats the air
causing a shockwave that produces the crack of thunder.
A severe storm, classified as one
that produces 1-inch hail, at least 58-mile-per-hour winds or a tornado,
develops from wind shear, or when wind changes in direction, speed and height. According
to the National Severe Storms Laboratory, there are about 100,000 thunderstorms
each year in the U.S. and about 10 percent of these reach severe levels.
While Lester described the
immediate reason for our thunderstorms, the cause for our wet spring that is
maintaining humidity and storm potential could have to do with climate change.
Montana State University earth
sciences professor Cathy Whitlock, the lead author of the Montana Climate
Assessment, projects an overall warming trend in the coming decades but also
says storm patterns are likely to change.
Whitlock was unavailable for an
interview at EBS press time, but in a 2018 interview with EBS she predicted
that Big Sky can expect similar precipitation amounts in the future, but
snowpack won’t last as long, spring floods are probable and late-summer droughts
are likely.
“We’ve seen periods in the past
when it’s been warmer than it is today, but we’ve not seen a rate of warming as
fast as is happening right now,” Whitlock said. “We can already see the effects
in Montana, across the country and around the world. We’re warming at an
alarming rate.”
The Montana Climate Assessment—a
product of the Montana Institute on Ecosystems—reports annual average
temperatures have risen across the state between 1950 and 2015 by about 2 or 3 degrees
F, while average winter precipitation in western and central Montana has
decreased by 1 inch and spring precipitation in the eastern part of the state
has increased by about 2 inches.
As noted in the report, Montana
experiences a highly variable climate and day-to-day weather as a result of
storm systems and air masses from the Pacific, Arctic and Gulf of Mexico. While
incredibly dynamic—recall the old adage “If you don’t like the weather in
Montana, wait five minutes,”—Montana’s climate directly impacts the state’s
economy, having effects on agriculture and recreation among others.
“I’ve come
to realize that climate change is really not a stand-alone issue,” Whitlock
said. “It affects all aspects of Montana’s economy and social well-being, and
it’s time for some serious discussion and planning.”