More than one friend sent me a link to a Yahoo! story today about how rainy forecasts are misunderstood. The article contends that only half of the population fully understands what the visual forecast icons and percentages mean.

What do I mean by visual forecasts?

Tuesday has a 50% chance of showers. What does that even mean? Let’s look at another example.

Monday and Tuesday of next week have a 40 and 50 percent chance of rain, respectively.

What confused people is what the percentage actually stands for. Many surveyed thought by saying “there is a 50% chance of rain” means that it will rain for half the day or only half the area will get rain. Although I can see what they are thinking, they are unfortunately wrong. The saying “50% chance” means given the atmospheric conditions at this time, half the time it rains and half the time it doesn’t.

As seen in the survey, this is a very common misconception. Meteorologists may not do a good enough job explaining this feature of the forecast. Some people don’t even use “chances of” on their extended forecasts.

My former boss at WTNH and good friend Geoff Fox never puts percentages on his 8-day forecasts. It is misleading to people, he would say. It took me a couple of days to understand what he meant.   A good communicator is just as powerful as an icon. Geoff does a great job of explaining each tricky forecast so not to mislead any viewers.

Next time you hear “there is a chance of rain” you’ll know what the meteorologist is talking about…even if we are only right 50% of the time.

With the summer solstice quickly approaching, the sun’s elevation angle in the sky increases daily. Higher sun angle means more luminosity per square meter. Low sun angle produces fewer rays per square meter. More intensity means more heat and, therefore, higher temperatures. 

A common question one may ask is, “If the sun reaches its highest elevation in our sky on June 21st, why then is that not the hottest time of the year?” The answer is the oceans. The oceans store heat (high specific heat capacity), therefore actual changes in mean Earth temperature are delayed by several weeks, i.e. the hottest days of summer are usually in late July or early August, over a month from the summer solstice.

Below, a graphic which represents the sun’s zenith angle/elevation angle for a latitude of 50 degrees North at the winter and summer solitices and equinox. Hartford’s latitude is roughly 41 degrees North. This means you would have to subract 9 degrees from the zenith angle or add 9 degrees to the elevation angle to calculate how far above the horizon the sun would be in the sky at these times.

UV Index

The Ultraviolet (UV) Index is an international standard measurement of how strong the UV radiation from the sun is at a particular time on a particular day. To read the American Meteorological Society’s definition of ultraviolet radiation, click here. The UV index is a scale primarily used in daily forecasts aimed at the general public.
 

UV index is dependent on many variables, including stratospheric ozone, sun’s elevation angle, latitude, time of day, altitude, weather conditions, air pollution, and surface reflection. UV rays can be further broken down into UVA, UVB, and UVC.

UVA (long wave) – The aging rays are equally intense year round at any time of the day. UVA damage is linked to premature aging, weakened immunity and a predisposition to skin cancer.

UVB (medium wave) – The burning rays are strongest at midday. UVB rays are associated with premature again, weakened immunity and the development of skin cancer. About 10% reach the Earth’s surface.

UVC (short wave) – The strongest and most dangerous, are filtered out by the ozone layer.

When conditions are right, UV indices can make it into the very high (dangerous) range in Connecticut. To help reduce the sun’s harmful effects, try reducing sun exposure between 10 am - 4 pm, applying sunscreen with SPF 15 or higher every 2 hours when outside, wearing sunglasses with UV–A and UV–B protection, wearing a wide-brimmed hat, and using lip balm with SPF 15 or higher.

SPF

What is SPF? SPF refers to Sun Protection Factor and applies only to UVB radiation. It is a multiple of how much time you can stay in the sun without burning your skin. For example, if you normally burn without any sunscreen in 10 minutes, a sunscreen with an SPF 20 would allow you to stay in the sun for 200 minutes without burning.

Tanning

The skin’s first defense against UV rays is melanin, a chemical present in a variety of colors and concentrations in most people’s skin that helps with defense from the sun. UV rays act upon melanin, causing the melanin to spread out or grow, increasing its presence in response to the sun’s exposure. The result is a “sun tan”. The darker the skin color, the more melanin the skin has for protection. Hence, fair skinned people are most susceptible to burning.

Questions people frequently ask are, “When is the best time of day to tan?” “How do I get the best tan?” The sun’s rays are most intense from 10 am – 2pm when it is highest in the sky. Obviously, the absence of clouds during this time frame would be the ideal time to tan. As mentioned earlier, surface reflection plays an important role in what happens to the UV rays once they reach Earth’s surface. Wading waist deep in water would be far more conducive to receiving a tan over playing wiffle ball on a grass field. The green grass would absorb but not reflect the sunlight the way in which water does. Essentially, the rays from the incoming UV rays and the reflected rays from the ground are “tanning” you at the same time. Please keep in mind that too much sun exposure could lead to sunburns, eye damage such as cataracts, skin aging, and skin cancer.

Research also suggests that being physically active, which increases blood circulation, increases the amount of melanin that will be pulled to the surface of your skin. One of the papers may be viewed here.

Common Myths

“Tanning beds and sun lamps are a safe way to get a tan.” False. UVA is emitted from tanning beds and sun lamps at rates of up to 5 times as much as the sun!

“After years of being out in the sun and not taking sun safety precautions, would starting now make any difference?” Definitely. Research has shown that being “sun safe” regardless of what age, you can reverse some of the damage that has been done while also slowing the appearance of further sun–related skin damage.

“There is no need for protection on a cloudy day.” False. Up to 80% of the sun’s damaging rays go through light clouds, haze and fog.

“People with medium to dark skin never burn.” False. Although people with medium to darker skin tend to tan more easily than others, they can still get sunburns. They can also suffer from overexposure to UV-light. It is still important for these skin types to use sunscreens and avoid being in the sun longer than they need to be.

“I heard that in order to get a suntan you have to burn first.” False. Sunburn does not fade into a tan. Sunburn indicates over exposure to UV-light and actually damages the skin, leaving it inflamed (as indicated by the skin’s red coloring and sensitivity), dry, chapped and visibly unappealing. In fact, sunburn can lead to premature aging and potentially skin cancer. Always practice moderation when tanning and use the proper sunscreen protection when tanning outdoors.

Capitol building in full bloom

Allergies affect different people at different times throughout the year. The three most common types of pollens are from trees, grasses, and ragweed. Allergic diseases are a major cause of illness and disability in the US, affecting more than 35 million people with upper respiratory symptoms. Pollen allergy (hay fever) is one of the most common chronic diseases.

The first allergy culprit of the year comes from tree pollen, which in Connecticut normally blooms in the months from March to June. Contrary to what many people believe, trees with brightly colored flowers usually do not bother allergy sufferers. Instead, the non-flowering plain looking trees cause the greatest allergy symptoms. Some of the top allergy producing trees in Connecticut are Oak, Birch, Cottonwood, Maple (begins in February), Hickory, Sycamore, Walnut, Beech, and Elm.

Weather plays an important daily role on the actual levels of the allergenic concentrations in the air. When the forecast calls for a warm, dry, breezy day, make sure you take antihistamines or use nasal sprays before venturing outside. These atmospheric conditions favor the greatest concentrations of airborne pollen as the wind transports small, light pollen grains away from the source (trees in this case) and into your nose.

On colder, wet, and more humid days, water vapor in the air condensates onto the pollen grains. This in turn makes the particles heavier, and less likely to be transported away from their source by the wind. This is also seen around daybreak (the coolest part of the day) before the sun comes out and heats up the surface of the earth. The moisture eventually evaporates from the surface of the trees, freeing the pollen and making it airborne again.

The graphic below displays the four day forecast for pollen levels around the Hartford area.

4day Pollen 4cast for Hartford Area

Allergy sufferers, stay updated on future weather forecasts and daily pollen reports.