The popular Discovery Channel show "MythBusters" has busted a myth or two in regards to weather over the shows history. In my opinion, not enough is being done to inform the general public about weather phenomena or myths that exist out there. So I figured I'd address a few popular questions I get and straighten out some myths that I hear.
Myth: "It has to be 32 degrees in order to get snow"
Truth: No, it doesn't have to be 32 degrees in order for snow to fall. We are taught early on (elementary/middle school) that 32 degrees is the freezing point of water. Rain is water, snow is frozen water. Water freezes at 32, thus snow falls at 32 degrees! At its most basic, this is true. But it goes much deeper than that. As the precipitation falls from the clouds, the drops create a frictional drag on the air surrounding the cloud. If enough precipitation falls (i.e. heavy shower/downpour), the drops (or snow) pulls the cold air down along with it, briefly lowering a snow level. That means if your car thermometer is reading 37 degrees but your seeing snow falling on your windshield, the shower has pulled the colder air from above down to the surface. A surface temperature of 38 degrees or higher would be pretty tough to support snow. In order for snow to accumulate, we would need the surface temperature to be freezing. That often requires several hours of air surface temperatures of freezing or below. The ground is only cooled from the air-exposed side because the ground tends to warm from below. This bit of information leads into my next fact.
Myth: "Bridges and overpasses are the first surfaces to freeze"
Truth: Absolutely true. Roads that are suspended from the earth's surface will reach freezing before the surface streets. This is because roads on bridges and overpasses are cooled from above and below, as compared to surface streets that are just cooled from above.
Myth: "If caught on the highway during a tornado, the safest place to be is an underpass"
Truth: This is a BIG no-no. You're better off in a ditch on the side of the road than stopping under an underpass. If a tornado crosses near or over and underpass, the underpass becomes a natural wind tunnel enhancing the winds as they pass under the road and making it a more dangerous spot to ride out a tornado. Along with the enhanced winds, an underpass creates a funnel for all the debris flying around the tornado turning debris into big bullets that can injure or kill you. If you can safely, exit the freeway and seek shelter in a nearby structure. But avoid the next myth...
Myth: "During a tornado, open the windows so that the storm won't damage the home"
Truth: Keep the windows closed! Here's the deal. Some folks think that the extreme pressure differences as a tornado passes will "blow up" or "explode" a home. Tornadoes don't "blow up" houses, it's damaging high winds rip the house apart. Opening windows won't equalize pressure from the storm to the inside of the house and won't prevent the tornado from destroying the house. All opening the windows does is invite that flying debris into the house and becomes another way that people can be killed from tornadoes. The best place to be in a house during a tornado is on the lowest level in a central location away from windows. If you have a bathroom with a tub, that works too.
Myth: "Hurricanes, Typhoons, and Cyclones are all different types of storms"
Truth: The only differences are where these storms form. They are all classified as tropical cyclones. Here in the Western hemisphere, we are familiar with hurricanes. In the Eastern hemisphere, they are known as typhoons (these storms often impact Taiwan, Japan, China). The term cyclone describes a tropical cyclone that forms in the Indian Ocean. Australia and surrounding areas have their own name for tropical cyclones, known as Willy Nillys.
Myth: "Water drains opposite in the Southern hemisphere"
Truth: This isn't exactly a "weather myth" but it is founded on a key component that is utilized in meteorology. First off, the myth is NOT true. Toilets flush the same way and water drains the same way in both hemispheres. But there is a difference in rotation on a larger scale between the two hemispheres. Here in the Northern hemisphere, our storms (known as cyclones) rotate in a counter-clockwise fashion. This is due to a force known as the Coriolis Effect. Coriolis essentially is an apparent deflection to the right as the earth rotates. Next time you take a plane ride, open up the in-flight magazine and check out the flight paths of the airlines. You'll notice that the paths are in an "arc" shape. If you tried to fly in a straight line from Portland to New York, you'd end up somewhere in Florida! So flight plans over-correct for this "deflection" to the right and the path becomes arc-shaped. The same thing happens in the Southern hemisphere, except the deflection is to the left. If you apply the Coriolis Effect to cyclones in the Southern half of the earth, cyclones will spin clockwise.
So if storms spin in opposite directions in the Southern hemisphere, why doesn't water drain in the opposite direction too? The Coriolis Effect only impact to large-scale features. The water in toilets and sinks are on too small a scale for any impact.
Myth: "It's a Monsoon out there!"
Truth: The above statement is often uttered when commenting on a heavy downpour. However, a monsoon is not a rainstorm. A monsoon is defined as a seasonal reversal of winds. The rains are just a result of the changes in winds. During the summer months, winds will come off of the ocean onto the land. That results in lots of rain as the air moving inland is very moist from the ocean waters. While the rains are the most well-known result of a monsoon, there is also a "dry" monsoon that occurs during the winter. As the winds reverse in the winter, air flows from land to sea. The air is much drier over land thus, the "dry" monsoon. A few of the famous monsoons are the South Asian (Indian) monsoon and the SW US monsoon (Arizona, New Mexico, Nevada, California, Utah). Oregon doesn't have a monsoon despite being located next to the ocean. We do see an impact of the SW US monsoon sometimes during the summer when afternoon thunderstorms pop up in a southerly wind setup. But now you know that when it rains, it's no monsoon!
How many of those did you already know? Do you have any questions you'd like answered?
Monday, March 26, 2012
Wednesday, March 7, 2012
February Report Card
January's grades weren't so hot. I've promised improvement. February offered another shot at some winter weather forecasting as well which may threaten that record being that is so difficult to forecast winter weather this late in the winter season. The grades for the second month fall like this:
I made a forecast for 18 days in February, I took a few sick days early in the month. That didn't stop the numbers from being the best so far. My temperature accuracy topped out at 88% (16/18) and conditions reached 100%. The two missed temperature days were off by 4 degrees.
A late-month snow threat had a near-perfect forecast with accurate temps and conditions. The timing and location of the forecasted snow-showers were predicted well, too. Winter weather forecasting becomes an issue this late in the month and season. The angle of the sun is on the increase as the days are getting longer. The way the sun angle works is like this:
During the winter, the sun angle is rather low. This means that the sun's energy is spread across a wider surface. That results in less heat across a larger area. As the summer months roll around, the sun becomes stronger. As the sun passes higher in the sky, it's energy is concentrated all on a smaller area at the surface. By the time we reach the end of February, our average temperatures are up to 54 degrees. That makes it difficult to get any sort of winter weather that would fall widespread down to the surface. We would need a good push of cold air from Canada in order to get that "wintery" weather. That's what happened in this case. Cold air sagged south from the boarder but it only brought temps down to the lower 30's. With those temperatures and enough moisture it becomes a borderline rain/snow event. Add in the strengthening sun angle, it becomes nearly impossible to forecast exactly where snow showers will pop up.
Despite the challenges, my forecast for those final few days of February were rather accurate. That was much to my surprise but the confidence from January's snow event definitely spilled over into February's "winter finale". As far as March's snow outlook, I think we can write it off. There is roughly a 1.5% statistical chance of snow in March.
I made a forecast for 18 days in February, I took a few sick days early in the month. That didn't stop the numbers from being the best so far. My temperature accuracy topped out at 88% (16/18) and conditions reached 100%. The two missed temperature days were off by 4 degrees.
A late-month snow threat had a near-perfect forecast with accurate temps and conditions. The timing and location of the forecasted snow-showers were predicted well, too. Winter weather forecasting becomes an issue this late in the month and season. The angle of the sun is on the increase as the days are getting longer. The way the sun angle works is like this:
During the winter, the sun angle is rather low. This means that the sun's energy is spread across a wider surface. That results in less heat across a larger area. As the summer months roll around, the sun becomes stronger. As the sun passes higher in the sky, it's energy is concentrated all on a smaller area at the surface. By the time we reach the end of February, our average temperatures are up to 54 degrees. That makes it difficult to get any sort of winter weather that would fall widespread down to the surface. We would need a good push of cold air from Canada in order to get that "wintery" weather. That's what happened in this case. Cold air sagged south from the boarder but it only brought temps down to the lower 30's. With those temperatures and enough moisture it becomes a borderline rain/snow event. Add in the strengthening sun angle, it becomes nearly impossible to forecast exactly where snow showers will pop up.
Despite the challenges, my forecast for those final few days of February were rather accurate. That was much to my surprise but the confidence from January's snow event definitely spilled over into February's "winter finale". As far as March's snow outlook, I think we can write it off. There is roughly a 1.5% statistical chance of snow in March.
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