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Fair runs hot and cool

Longtime residents often say fair time is hot time in the North County. The Mid-State Fair starts Wednesday and continues through July 31. Even though the afternoons can be sizzling hot, there’s nothing quite like a balmy summer’s evening in Paso Robles.

However, this certainly wasn’t the case in Paso Robles last week as a persistent low-pressure trough north of California extended across the Pacific Northwest and produced below-normal temperatures. Wednesday, Thursday and Friday only saw the maximum air temperatures reached the high 70s at the Paso Robles Airport. Usually the average maximum temperature in Paso Robles Airport at this time of the year is about 94 degrees.

Last year’s Mid-State Fair was one of the coolest on record. Much like last week, there were a few days that didn’t even reach the 80-degree mark and only on one day did the temperature hit the century point. In contrast, the 2009 Mid-State Fair had temperatures approaching 106 degrees. The warmest temperature ever recoded at the Paso Robles Airport during July was 115 degrees, measured in 1960.

For this year’s fair, a high-pressure ridge will replace the low-pressure trough and average to above average seasonal temperatures should develop.

With the warmer temperatures at the fair, we should be able to hear thousands of chirps from the local crickets after the concerts have ended. Studies have shown that the frequency of chirping varies according to the temperature. You can count the number of chirps in 15 seconds and then add 37. The number you get will be an approximation of the outside temperature in degrees Fahrenheit.

Temperature can be defined in many different ways. For example, temperature can be expressed as the average kinetic energy of each atom. The way I like to think about it is how fast the atoms and molecules of a substance are zipping back and forth or vibrating. The faster air molecules move, the greater the friction between them and the higher the temperature will become, like rubbing your hands together briskly.

One way to increase friction and consequently air temperature is squeezing air molecules tighter together by increasing air pressure. You probably noticed this when filling up or pressurizing a bicycle tire or scuba tank, it heats up.

During the long days of summer, areas of high atmospheric pressure can move or develop over the Central Coast. These highs push air from upper levels of our atmosphere toward the ground, where it becomes compressed and warmed by pressure (compressional heating).

Sometimes these areas of high pressure can block cooler weather systems from arriving along the Central Coast. The longer the stationary high remains, the warmer the temperatures will become. Without cloud cover, the sunlight is free to hit the ground with all its might, producing a heat wave. But, as my dad would often say, heat waves rarely last more than three or four days along coastal California before the fog comes rolling in and cools things off.

Today’s forecast

A deep upper-level low off the coast of Victoria Island, Canada, with an associated trough extending southward off the California coast will move northeastward over the next 48 hours.

This condition will produced warmer temperatures today through Tuesday.

After the marine layer burns off later this morning, today’s temperatures will range from the low 60s along the northwesterly facing beaches (Montaña de Oro, Los Osos and Morro Bay), while the southwesterly facing beaches (Cayucos and Avila Beach) will range between the high 60s to the low 70s.

The coastal valleys (San Luis Obispo) will range between the low to mid-70s today and the North County (Paso Robles) will warm to the mid- to high 80s.

Night and morning coastal low clouds, areas of drizzle and fog will redevelop tonight into Monday morning.

Another low pressure system will drop south Tuesday, bringing extensive coastal low clouds and drizzle to the Central Coast on Tuesday night into early Wednesday morning. As this low-pressure system moves south of San Luis Obispo County and the eastern Pacific high strengthens to 1,035 millibars, a steep pressure gradient will develop along the California coast.

This gradient will produce strong to gale force (25- to 38-mph) northwesterly (onshore) winds along the coast Wednesday through Thursday. These winds will help to mix out the marine layer and produce a greater amount of sunshine along the coast.

Gradual warming will occur Thursday and Friday with Mid-State Fair temperatures approaching normal and coastal locations under night and morning low clouds with below-normal temperatures. Surf report

Today’s 3- to 4-foot northwesterly (310-degree deepwater) sea and swell (with a 5- to 8-second period) will remain at this height and period through Tuesday morning.

Strong to gale force (25- to 38-mph) northwesterly winds will generate a 5- to 7-foot (310-degree deep-water) sea and swell (with a 5- to 9-second period) Tuesday afternoon through Friday.

Arriving from the Southern Hemisphere: Normally, storms in the Tasman Sea never produce any swell along the California coast. However, last week’s storm was one of the strongest I have seen.

A 1-foot Southern Hemisphere (245-degree deepwater) swell (with an 18- to 20-second period) from this storm will arrive along our coast Monday, increasing to 1 to 2 feet (with a 15- to 17-second period) Tuesday and Wednesday.

Seawater temperatures will range between 54 to 56 degrees through Tuesday, decreasing to 52 to 54 degrees Wednesday and Thursday.

Summer is here, which means lots of fun in the sun! Nevertheless, the weather can get extremely hot and quickly go from fun to dangerous. Extreme heat can be life-threatening. So learn what extreme heat is and how you can protect yourself. To learn more, please go to www.pge.com/myhome/edusafety/seasonal/coolingcenters/summersafety.shtml

John Lindsey, media relations representative for PG&E and a local weather expert, has lived along the Central Coast for more than 24 years. To subscribe to his daily weather forecast or ask him a question, email him at pgeweather@ pge.com.

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