Tuesday, June 28, 2011

Summer BEFORE July 4th?

Summer officially started June 21st. But here in the Pacific Northwest, residents often live by the creed, "Summer actually starts on the 5th of July". It has been a decent start to the Summer here in Portland. A 80 degree day here or there. But even better news is showing up on the weather maps! Let's take a look.

Our first bit of evidence is the 500mb map. This is halfway up the atmosphere and shows us overall ridge (good) and trough (bad) patterns.

Here is the 500mb map valid last night for July 4th around 11 a.m. Look at the ridge that covers most of the West and extends all the way into northern Canada! This is a great set up for a nice stretch of warm, sunny conditions! Other maps re-enforce this fact.

The map above is our 850mb map. We use this map to locate areas of warm air and areas of cold air. We can track their movement with this map. The red contours on the map are isotherms, lines of constant temperature, in degrees Celsius. Temperatures at the 850mb level loosely translate to specific temperatures at the surface. This map, again valid last night (June 27th) shows the conditions for late morning on the 4th. The 15-degree isotherm is just to our east. If we estimate the 850 temp to be about 14 degrees Celsius above Portland, that would translate to an 80-degree day! Plenty of time for it to change, one way or another, but the warm temperature fits the above 500mb map we looked at!
Here is your surface map for the Fourth of July! Looks awesome! Precipitation is nowhere to be seen. Also not the high pressure system out off the southern Oregon coast. That helps send any sort of wet systems well to our north! Any time we see surface pressure around 1020, that means good things. The 1020 isobar (lines of constant pressure) is right in our neighborhood. Average surface pressure is right around 1013. The higher the pressure, the better the conditions!

We have concluded our investigative work! Weather forecasting works like an investigation. Start with one map, and try to find validations on all the others. In our 4th of July case, things are lining up in a good way! Maybe this year, Summer in the NW starts early!

Friday, June 17, 2011

Waiting For Arlene

Many of you may not know who Arlene is. That's ok, she was overshadowed by some of her more famous sisters. She last showed up in June of 2005. She came to the Southern U.S. from Honduras and killed a person. She was the first of her kind that year, many others followed and did far worse things.

Of course I am talking about Tropical Storm Arlene. She made landfall about 6 years ago to the date. For a tropical storm, she was a large one. Just missing hurricane status. But she ushered in one of the most active and historic hurricane seasons on record! Her more famous sisters are known as Hurricane Katrina and Hurricane Rita. There were 26 named storms in 2005, so many that we ran out of names and had to use names from the Greek alphabet for the remaining storms.

2011 tropical season is underway, it began June 1st. So far, the Atlantic basin has been quiet. But forecasters have warned that it will not remain that way as the season progresses. The Climate Prediction Center says the Atlantic will see 12-18 named storms, 6-10 of which may reach hurricane status (sustained winds over 1 minuet that measure at least 74 m.p.h). Of the named storms, the CPD says that 3 to 6 of them may become major hurricanes (Cat. 3 or higher, winds at least 111 m.p.h.). This would equate to what is referred to as a "hyper-active" hurricane season. 2005 definitely qualifies as a hyper-active season, and we just endured one last year. 2010 was an active, yet rare year. 19 named storms in the Atlantic and NOT ONE of those storms made landfall in the U.S. This is very rare.

Your probably asking yourself, "How can they forecast an entire hurricane season when they can't even predict the weather 36 hours out?!". There are signs but before I talk about those that are scientific, I want to just brush over a little research I did.

The U.S. has had a wild Spring. A record amount of tornadoes and severe weather in general across much of the country has us praying for that Summer weather to give us a break. I decided to look at past Springs and the amount of severe weather and compare it to the following Hurricane Season.

Last year, we had 1,543 reported tornadoes. As I mentioned above, 2010 had 19 named storms but none made landfall. 2009 had 1,305 tornadoes and nine named storms (1 landfall). 1,685 tornadoes were reported in 2008 and we had 16 named tropical storms that Summer (3 landfalls). 1,102 tornadoes and 15 named storms (1 landfall) in 2007. 1,117 tornadoes and nine named storms for 2006. Our active hurricane season in 2005 (26 named, five landfalls!) only had 1,262 tornado reports. Finally, 1,820 tornadoes were reported in 2004 with 15 named storms (three landfalls). Breaking down the stats, it is somewhat difficult to draw correlations between active Springs and Summers. So far this year, there have been 1,482 preliminary tornado reports. Those haven't been all confirmed yet. But still a high number. What will that translate into for this Summer?

Let's talk about trends that DO correlate to an active tropical season. We will begin with sea water temperatures. Warm water is "fuel" to a hurricane so the warmer the water, the better a chance to get storms to fire up and strengthen. The Atlantic waters are impacted by what happens off of our coast here in the Pacific. Our cool Spring can be credited to the cool, La Nina conditions. The La Nina typically gives us cooler than normal ocean waters here in the Pacific. The main goal of the ocean is to balance itself out. If we have a cold Pacific, the oceans will make up for it by having a warm Atlantic. Warm waters in the Atlantic means a good amount of "fuel" for storms this Summer!

Warm surface waters mean provide the atmosphere with a lot of uplift. When the sun strikes the warm waters and warms the air around it, that air will begin to lift. And guess what lift means for storms? You got it! Rising motions in the atmosphere help aid hurricanes and all storms for that matter! Now we have warm waters in the Atlantic and that means plenty of uplift for our storms.

Here is a map of 2010 and the storm tracks of those 19 storms that Summer.
Note how many made their way into the Gulf of Mexico. As only one storm tracked into the Gulf, that could mean a lot of untapped energy will remain for this hurricane season. As a tropical storm or hurricane makes its way through the warm Gulf, it feeds off the warm waters. When that warm surface waters get used up, the ocean pulls up cooler water from below to replace that warm water. The more storms that track through the Gulf, the less fuel for the next storms to use. With only one storm moving through that area last year, that could mean plenty of leftover energy just waiting to be used this year!

So there are the "proven", scientific reasons as to why we could see a very active, fun but dangerous 2011 Atlantic Hurricane Season.

Friday, June 3, 2011

Portland's Spring Weather: In Pictures

One of my favorite parts about my job are the viewer emails that we receive on a daily basis. Most emails are VERY opinionated stances on stories or programming (one of my personal favorites being a complaint about the station not airing a classic Perry Mason re-run. You know, the one where Perry wins the case?). Those emails are a story for another day. But during crazy weather times, which we have had plenty so far this year, we do receive some very cool photos! I thought I would share a few of them with you all.

This first photo was taken earlier this Spring. These are some of the most unique cloud forms, it's easy to see why! Sometimes referred to as flying saucers or "the mothership", the scientific name for these clouds is "lenticular clouds". They form over hills or mountains as moisture in the atmosphere is forced to rise over the geographical barrier and forms a cloud. The size of the cloud is normally determined by the jet stream above, causing shear to the cloud, or tearing of the cloud. In the above photo, you can see the jet stream is pushing the cloud from the left side of the photo to the right. Look at the top right-hand side of the cloud. You can see the tops of the cloud being pushed down-wind (to the right). These clouds will appear stationary, giving it that hovering, "mothership" look. In fact, the cloud is repeatedly fed moisture from the air and just re-generates a new cloud. As the air moves down the back side of the hill or mountain, the moisture in the air evaporates, thus no cloud! If you look towards Mt. Hood on a clear day, you can often see a "cap" over the top of the mountain. The cool thing about lenticular clouds is that they don't generate any precipitation and are typically a sign of fair conditions!

Our next photo depicts a visually stunning but dangerous cloud!
This photo was sent in from Woodburn. But it looks very similar to a cloud that people in the South and Midwest have seen lately. I am fairly certain that this is a cloud known as a "wall cloud". The reason why I am not 100% sure is that in order to confirm it, there would have to be rotation. But judging from the photo, I feel confident that this is a rare wall cloud in Oregon! Why is this cloud rare in Oregon? Because we only average 2 tornadoes a year! This low-hanging cloud formation is often a significant indicator of a tornado. This storm setup has a large amount of air at the surface being sucked into the storm. Imagine air from the left side of the photo being sucked into the central portion of the storm. As the air gets sucked into the storm, it quickly cools and condenses into a cloud that forms at a lower elevation. Research has shown that the lower the level of the wall cloud, the more likely a tornado is to spawn. All that being said, this storm did not tornado. The environment has to be just right and most times the ingredients just aren't there for the development of tornadoes. But if you notice this low-hanging cloud in the future...probably best to take cover, just to be safe!

The final picture I have today could be considered a cloud "relative" of the wall cloud.
What we are looking at are the low-hanging clouds at the base of the ominous dark cloud. The clouds appear right above the rooftops of the buildings in Vancouver. While very similar to a wall cloud, these clouds known as "scud" are actually smaller, often rugged individual clouds. Scud clouds form when moist, cool air falls out of the storm, this is known as the outflow. The outflow forces the warmer air around the outside of the storm to rise. As the warmer air rises, it cools and forms a cloud. So these Scud clouds are indicators of a cool outflow from the storm!
It is easier to make out the individual clouds in this photo. They just kind of linger around the base of the storm. Because they hang around the base of the storm, they often times get confused as wall clouds. This is not the case as Scud clouds do not spawn tornadoes.

There was a brief look at what has been happening around Portland this spring. The wall and scud clouds are very rare for Oregon and the NW as a whole but do occur. Lenticular clouds, on the other hand, are quite common for us. The Cascade mountain range offers us plenty of opportunities for lenticular development on top of all those mountains!