Have you ever watched the television game show “Are You Smarter Than a 5th Grader?” The show tests whether adults know as much as elementary school students? I thought of it recently while teaching a group of enthusiastic and dedicated science teachers how to make homemade barometers.
Earlier this month, professor Grace Neff hosted a group of fifth-grade science teachers from San Luis Obispo County at the Central Coast Science Project on the Cal Poly campus. The goal of this workshop was to introduce innovative ways to teach science to fifth-graders. A diverse group of presenters from NASA to the State Parks Department spoke about a wide range of science subjects from astronomy to biology over a five-day period.
Cal Poly professor Bob Echols and I had the honor to teach about weather. We used real-life, hold-in-your-hand experiments: a cloud in the bottle, fire cylinders and the lightning-fast crush can, all designed to teach about air pressure.
For many students, it’s difficult to get a good grasp on the subject. But when it comes to weather forecasting, air pressure is one of the most important factors.
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Atmospheric pressure along the Central Coast often shows a diurnal cycle — a daily rotation repeated every 24 hours — especially during the summer months. This cycle is caused by faster warming of the air mass over the inland valleys than over the Pacific.
As the air in our inland valleys warms up, it becomes less dense, producing a thermal low, which often produces increasing northwesterly (onshore) winds during the afternoon hours.
At night, the opposite occurs, with the air mass over the inland valleys cooling faster and becoming denser. This condition often produces northeasterly (offshore) winds. Of course many other factors can affect the winds.
From late fall into spring, dropping air pressure may be a sign of rain and increasing air pressure often means sunny days.
A good way to allow students to get their arms around the concept of air pressure is to observe a barometer, an instrument that measures pressure. Professor Echols brought my favorite: an easy-to-make jar barometer that you can build with stuff lying around your house.
To construct a homemade barometer follow these instructions.
1. Find a clean wide-mouth mason jar and remove the lid.
2. Cut a 15-inch balloon in half.
3. Stretch the balloon over the top of the jar, to form a lid. Hold the balloon in place with a strong rubber band, making as airtight a seal as possible.
4. Attach one end of a straw to the jar’s balloon lid close to the middle with tape. One-quarter of the straw should sit on the lid itself, while the other three quarters should hang off into space.
5. Glue or tape a small toothpick to the end of the straw that’s hanging off in space. The toothpick will produce greater precision and accuracy.
6. Place the jar next to a piece of paper, with the straw and toothpick parallel to the paper. Air trapped inside the jar expands with low atmospheric pressure or contracts with high atmospheric pressure. The surface of the balloon changes shape and raises or lowers the end of the toothpick pointer.
7. Mark the position of the toothpick against the paper each day.
A toothpick that rises indicates increasing air pressure and a toothpick lowers indicates dropping air pressure.
You can calibrate your jar barometer by checking the barometers at the San Luis Obispo or Paso Robles airports which are corrected to sea level pressure by visiting www.wrh.noaa.gov/lox/.
You should place your jar barometer in an area with constant temperature as changes in temperature will also cause your barometer to expand or contract.
On the last day of the Mid-State Fair, subtropical moisture will stream overhead from the southwest and will produce variably cloudy skies and higher dew point temperatures.
These mid- to high level clouds will produce cooler temperatures in the North County and coastal valleys. However, the higher relative humidity levels will make it feel warmer and a bit muggy.
This monsoon moisture will trigger widespread thundershowers across the Sierra and a chance of thundershowers over the eastern regions of San Luis Obispo County and higher elevations of the coast range.
Subtropical moisture will also limit or maybe even eliminate the marine layer along the coastline this afternoon.
Today’s temperatures will range from the mid- to high 60s at the beaches and across coastal valley to the high 80s at the Mid-State Fair.
The cooling trend will continue Monday as a Gulf of Alaska trough of low pressure begins to swing southward across the west coast, with Central Coast temperatures trending to generally below normal through Tuesday.
By about Wednesday, the coastal marine layer should be very deep and strong to gale force (25- to 38-mph) northwesterly (onshore) winds along the coastline will continue to produce mild temperatures.
It appears the cool pattern will continue into the second week of August as well, especially at locations closer to the coast.
Today’s 2- to 4-foot northwesterly (310-degree deepwater) swell (with an 8- to 10-second period) will continue at this height and period through Monday.
Increasing northwesterly winds along the coast will generate a 3- to 4-foot northwesterly (320-degree deepwater) sea and swell (with a 5- to 8-second period) Tuesday.
Strong to gale force (25- to 39-mph) northwesterly winds will generate a 4- to 6-feet northwesterly (320-degree deepwater) sea and swell (with a 5- to 8-second period) Wednesday through Friday.
Arriving from the Southern Hemisphere:
Today’s 1- to 2-foot Southern Hemisphere (190-degree deepwater) swell (with a 13- to 15-second period) will gradually decrease through Monday.
A 1- to 3-foot Southern Hemisphere (210-degree deepwater) swell (with a 16- to 20-second period) should arrive along our coastline Thursday and will remain at this height but with a gradually shorter period through Saturday.
The relaxation of the northwesterly winds over the last few days has produced warmer seawater temperatures. Seawater temperatures will range between 58 and 60 degrees through Wednesday, decreasing to 55 to 57 degrees Thursday and Friday.
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John Lindsey, media relations representative for PG&E and local weather expert, has lived along the Central Coast for more than 25 years. To subscribe to his daily weather forecast or ask him a question, email him at firstname.lastname@example.org.