Heat expected to blast Valley today

Predicted high of 104 degrees would break a record set a year ago.

Published online on Saturday, May. 16, 2009

It's not exactly a heat wave, but a one-day weather spike is expected to bring an uncomfortable record to Fresno this afternoon.

The mercury is forecast to reach 104 degrees in Fresno today, breaking a record for this date of 102 degrees that was set just a year ago.

Unlike 2008, however, when May 17 marked the first of three straight daily records above 100 degrees, forecasters say Valley temperatures will settle back down Monday as a weather system muscles a high-pressure ridge out of the way.

The one-day jolt of heat -- from forecast highs of 98 degrees on both Saturday and Monday -- is unusual for this time of year, said Carlos Molina, a National Weather Service meteorologist in Hanford. A high-pressure ridge will be parked over Central California today.

"Think of it as a blanket that holds the heat in," Molina said. But on Monday, a disturbance pushing from the Pacific Ocean into the northwestern U.S. is expected to push that "blanket" off to the east.

"Typically what happens is a high-pressure ridge is strong enough that it won't budge," Molina said. "Normally we'd see three or four days of 100-degree heat before it cools down."

High temperatures for the rest of the week are forecast to be in the upper 80s to mid 90s through Friday. "We may stay below 100 until the end of May," Molina said.

Local attractions that rely on hot weather to drive attendance are looking forward to good crowds today.

The Island Water Park in northwest Fresno is sold out for a private company gathering, said supervisor Valerie Richardson, but this is normally the time of year when business really kicks into high gear.

Across town, Wild Water Adventure Park east of Clovis is anticipating a big crowd. Director Bob Martin said his staff may see as many as 5,000 to 5,500 people today.

"That's strictly because of the heat," Martin said. "We can kind of predict what attendance will be if it's 85 degrees or 95 or 105."

A year ago, Martin added, the park drew 3,200 people.

Whether the thermometer is in the 90s or the 100s, warm weather is quickly melting what snow did accumulate in the Sierra Nevada over the winter.

The state Department of Water Resources reported that many foothill reservoirs, including Millerton Lake and Pine Flat Reservoir, are near or above their average levels for this time of year as icy snowmelt flows into them.

Behind Friant Dam north of Fresno, Millerton Lake is 97% full, and the water level Saturday was seven feet below the spillway. The San Joaquin River was carrying 5,460 cubic feet, or nearly 41,000 gallons, of water into the lake every second. Ordinarily, the lake holds about 385,000 acre-feet of water this time of year, but Saturday's storage was 131% of normal, at nearly 505,000 acre-feet.

On the Kings River, the million-acre-foot Pine Flat Reservoir east of Fresno was less than two-thirds full, but it's at 92% of its average storage for the date. On Saturday morning, water was flowing into the lake at a rate of 8,800 cubic feet, or about 66,000 gallons, every second.

An acre-foot is approximately 326,000 gallons -- not quite enough water to flood a football field to a depth of 12 inches.

What people tend to forget is that while the weather may be hot, mountain rivers and streams are decidedly not. "It's basically melted snow," Molina said, sometimes just a few degrees above freezing.

"Even though a stream or river looks cool and inviting, the water is actually very cold and may be dangerously fast," the weather service warned Saturday in a special weather statement. "Outdoor enthusiasts are advised to use extreme caution near streams and rivers."