Oskaloosa.com

CNHI/Southeast Iowa

July 23, 2013

Heat burst hits Knoxville

KNOXVILLE — For 15 minutes last night, Knoxville's temperature rose by almost a degree per minute as the area was caught in a heat burst.

The National Weather Service says the event took place beginning at 10:55 p.m. Temperatures rose from 70 degrees to 84 degrees.

At the same time, the dew point plunged from 63 to 48 degrees as the warm, dry air spread.

Meteorologist Frank Boksa said that's pretty standard for the phenomenon.

There are a couple of aspects involved with a heat burst. One is the basic mechanics of a thunderstorm, which has both an updraft that feeds warm, moist air into the storm, and a downdraft that takes air out.

As that downdraft falls, it passes through different layers of air. The mid-level air can be warmer than air at the top of the thunderstorm or at the surface, and can also be drier.

“It generally is some warmer air, drier air at the mid levels,” Boksa said.

“Typically, warm air rises so you don't see that at the surface,” he continued. When that warmer level gets caught in a thunderstorm's downdraft, it falls. “You're taking that warmer air and pushing it to the surface.”

The result was evident last night. A wind gust with the storm hit 73 mph during the heat burst as the mid-level layer was slammed to the ground. Temperatures skyrocketed, but the air was much drier than what it was replacing.

As storm effects go, that's not the worst Iowa saw on Monday. Large hail hit a number of areas, with Newton reporting 0.88 hailstones. The largest may well have been in Stratford, northwest of Des Moines, where people posted photos of 1.5 inch hail.

Forecasters expect the weather to calm down considerably for the rest of the week. Temperatures are forecast to be below normal, with little chance of severe weather.

1
Text Only
CNHI/Southeast Iowa
  • Affirmative action ruling challenges colleges seeking diversity

    The U.S. Supreme Court's support of Michigan's ban on race-based affirmative action in university admissions may spur colleges to find new ways to achieve diversity without using racial preferences.

    April 23, 2014

  • A 'wearable robot' helps her walk again

    Science is about facts, numbers, laws and formulas. To be really good at it, you need to spend a lot of time in school. But science is also about something more: dreaming big and helping people.

    April 23, 2014

  • Cuba is running out of condoms

    The newest item on Cuba's list of dwindling commodities is condoms, which are now reportedly in short supply. In response, the Cuban government has approved the sale of expired condoms.

    April 23, 2014

  • Tulip Time schedule

    Tulip Time is just around the corner. Here's the complete schedule for events.

    April 23, 2014

  • The waffle taco's biggest enemy isn't McDonald's. It's consumer habits.

    Gesturing to Taco Bell, Thompson said McDonald's had "not seen an impact relative to the most recent competitor that entered the [breakfast] space," and that new competition would only make McDonald's pursue breakfast more aggressively.

    April 23, 2014

  • Life and Times cover.tiff Life and Times

    Click here to go to the new Life and Times e-magazine.

    May 30, 2012 1 Photo

  • Screen Shot 2014-04-22 at 4.42.47 PM.png VIDEO: Leopard attacks crowd in India

    A leopard caused panic in the city of Chandrapur when it sprung from the roof of a house and charged at rescue workers.

    April 22, 2014 1 Photo

  • The top 12 government programs ever

    Which federal programs and policies succeed in being cost-effective and targeting those who need them most? These two tests are obvious: After all, why would we spend taxpayers' money on a program that isn't worth what it costs or helps those who do not need help?

    April 22, 2014

  • In cuffs... 'Warlock' in West Virginia accused of sexual assault

    Police in West Virginia say a man claiming to be a “warlock” used promises of magical spells to lure children into committing sexual acts with him.

    April 22, 2014 1 Photo

  • Cats outsmart the researchers

    I knew a lot had been written about dogs, and I assumed there must be at least a handful of studies on cats. But after weeks of scouring the scientific world for someone - anyone - who studied how cats think, all I was left with was this statement, laughed over the phone to me by one of the world's top animal cognition experts, a Hungarian scientist named Ádám Miklósi.

    April 22, 2014

Obituaries
Oskaloosa Shopper
Facebook
Hyperlocal Search
Premier Guide
Find a business

Walking Fingers
Maps, Menus, Store hours, Coupons, and more...
Premier Guide
Parade
Magazine

Click HERE to read all your Parade favorites including Hollywood Wire, Celebrity interviews and photo galleries, Food recipes and cooking tips, Games and lots more.
Photo reprints