Summer’s arrival is filled with positive associations for many — beach vacations, the end of the school year, more hours of sunshine.

Unfortunately, it can also prompt headaches for car owners: As outdoor temperatures rise, so do larcenies, slashed tires, smashed windows and spray-painted doors.

The spike in crime in the summer is a fairly consistent pattern in Northern Virgnia and elsewhere. In the past, vehicle larcenies have generally been less frequent during colder months, with the most cases often reported in June, July and August, according to data from the Loudoun County Sheriff’s Office.

The sheriff’s office documented 91 vehicle larcenies in May 2010, a number that appeared to drop this year, with 44 vehicle larcenies reported from May 1 to 21. But after recent rashes of car vandalism in Sterling, Ashburn and Leesburg, authorities are reminding car owners to take basic steps to thwart would-be thieves.

“A lot of our cases, especially with larcenies in vehicles, it’s just car-hopping,” said Kraig Troxell, spokesman for the sheriff’s office. “They’re looking for unsecured cars, opening up the doors and pulling out whatever they can.”

All too often, people leave items of value — Global Positioning System units, wallets and laptops — in unlocked cars or in plain sight, Troxell said.

In most cases, thieves zero in on unlocked cars, Troxell said. But a window is more likely to be smashed if a valuable item is visible inside a locked car.

“This is usually a crime of opportunity,” he said.

Although targets of theft are often predictable, a recent spike in vandalism — including more than 40 vehicles in Ashburn and Sterling that have been damaged by perpetrators who spray-painted “68” on the cars — seems random in nature, authorities said.

The appearance of the number 68 painted on car doors began in late April and continued periodically throughout May, Troxell said. About 12 cars were vandalized in Sterling early Tuesday, authorities said.

The sheriff’s office said that it received a number of tips in connection to the incidents but that it had no lead on possible suspects.

“There is nothing indicating that it is gang-related,” Troxell said.

Most of the damage was done overnight or on weekends, which could indicate that juveniles are responsible, he said.

The investigation into the vandalism is ongoing, Troxell said.

Although more densely populated communities in eastern Loudoun tend to be the most popular spots for car-related crime, “you do see it in western Loudoun, as well,” Troxell said, noting reports of larcenies in areas such as Purcellville and Lovettsville.

“The numbers aren’t as high,” he said of the more rural areas. “It’s a lot harder to car-hop in Purcellville as opposed to Ashburn or Lansdowne or Sterling, where you can walk along the street and hit 10 or 15 cars in a block or so.”

The Leesburg Police Department also reminded residents to guard against burglary after approximately 27 cars parked on Glade Fern Terrace were damaged early May 26.

Leesburg police arrested Yonathan Melaku, 22, of Alexandria in connection to the Leesburg vehicle tampering. Melaku was charged with four counts of grand larceny, authorities said.

“It is not only important to lock cars, but to remove or hide items of value,” Leesburg police advised residents in a statement.