New Adventures

My journey in meteorology brings me to another adventure. I am leaving home today to start a summer research program (REU) in the National Weather Center at the University of Oklahoma, that I visited during SWFEx in May 2013! I’ll be driving 19 hours this weekend, quite the road trip! I’m feeling incredibly excited, but also a little nervous. Nineteen hours is pretty far from home. It’s weird packing up my essentials to move to a different university during the summer, as I’ve grown accustomed to the annual move to UNCA. However, I’m really excited to meet new friends (the REU students are all from different schools) and other scientists and professionals in Norman, Oklahoma! I will be doing research on a topic in meteorology, working with mentors to produce a paper and presentation by the end of the summer. Of course, I’ll be working in one of the weather capitals of the world, with so many people doing incredible forecasting and research in meteorology! As always on trips, it is a little surreal that I will soon be in an entirely different location, experiencing new things and learning more about the world (and myself).

It’s also weird that my time at UNCA is starting to come to a close, even though I have so many goals left to accomplish. This summer, I will be mulling over graduate school options, as this program will help me consider research and graduate school as a career. I hope I can get a lot of experience this summer, to boost me into my senior year. My goal is to blog regularly, but I’m not sure if these posts will be more experience/pictures-based or more about my research. Perhaps a little of both. Time to hit the road!

Weather Awareness

I was out shopping for a new weather radio yesterday, without much success. At one store, I was told, “We don’t carry them all year, only during hurricane season.” Huh? I think we get more severe weather in the spring and summer than hurricanes, even though the storms (generally) aren’t as fierce as they are out in the Plains! Stay weather aware all year; don’t wait for “severe weather season” or “hurricane season” (May 15th to November 30th) to pay attention. Case in point: Tropical Storm Ana just impacted the Southeast this week. Weather does what it wants, whether it is the proper season or not! And with that, I’ll step off my soapbox.

Thunderstorm Terminology

This is my first post in a new series of blogs, where I’m hoping to: (a) provide some basic information about confusing weather topics, and (b) have a new sense of motivation for writing blog posts on a regular basis.

What does it mean when a weather forecaster says, “Expect scattered thunderstorms this afternoon”? What about “isolated thunderstorms”, or “widespread storms”? I will try to explain these common terms used to describe the thunderstorms that are so common during the summer months. Disclaimer: The following is my opinion, and may or may not be standard practice for the weather forecasting industry. However, I would like to believe that it represents a typical classification of thunderstorms.

When I hear the phrase “isolated thunderstorms”, I think of a predominantly sunny region with one or two thunderstorms in the area. Nearly everyone doing outdoor activities will have no weather troubles. Nonetheless, there may be a couple of people who are unlucky enough to have a thunderstorm interruption. The weather radar picture often looks something like this:

Screen Shot 2014-08-11 at 3.05.15 PM

Isolated thunderstorms (one or two storms southwest of Miami).

How about “scattered thunderstorms”? To me, this means a greater coverage of storms. At this point, some people’s outdoor activities will be impacted, but not all. A good number of people will see sunny skies all afternoon and might wonder why the forecaster called for a “40% chance of thunderstorms”. (There was a good chance of storms, not a guarantee.) The radar picture for scattered storms might look something like this:

Screen Shot 2014-08-11 at 3.01.41 PM

Scattered thunderstorms.

Finally, what about “widespread” or “numerous” thunderstorms? I see this as a significant amount of rainy, stormy weather. Almost everyone will see some impact from an afternoon of numerous thunderstorms. In this case, it would be rare to find a person that was not impacted by the storms. Some radar examples of this include the following:

Screen Shot 2014-08-11 at 3.07.21 PM

Numerous thunderstorms (only in the area north of Tampa and Orlando, FL).

Screen Shot 2014-08-11 at 3.02.21 PM

More numerous thunderstorms (a close-up of the area in the previous picture).

Another example of “numerous thunderstorms” can happen if the storms travel in a continuous line. In cases where there is a line of storms, most people will experience storms, just not all at the same time. I would still consider this an example of “numerous thunderstorms”, with a timing caveat:

Screen Shot 2014-08-11 at 3.04.05 PM

A line of numerous thunderstorms moving to the south-southeast.

Each weather forecaster or meteorologist will use different words to describe thunderstorm activity, but I’ve just picked the most common ones to describe here. If you have any questions or suggestions, feel free to leave a comment below. Also, if you have an idea for a future topic, please leave a comment as well. My goal is to write a blog post like this every Wednesday, which I’ll call “Weather Wednesdays.” (Really, every day is weather day for me, but I’m always an advocate of alliteration.)

New Writing Topics

This blog is, once again, on shaky ground due to a quiet, dry summer with not much interesting, dynamic weather to write about. Also, the 3-month break from school has left me in a very lazy frame of mind. A bad combination like this leads to the writer’s block (laziness) I’m having.

But today, I have a new idea. What if I write occasional (weekly?) blog posts about confusing topics about weather and weather forecasting? From a “general public” point of view, the weather seems more confusing than ever before, with the rapid spread of information (mainly aided by social media) about weather and forecasting. I’m thinking about writing once a week about a single topic, weather phrase, or phenomenon (e.g. what causes a tornado outbreak, the meaning/difference between scattered vs. isolated thunderstorms, what is the polar vortex, etc.), hopefully explained well enough that anyone can understand it. I’ll tentatively label these blogs “Weather Wednesdays”. Obviously, these posts could range in length from a short paragraph to a 8-10 page thesis paper, depending on the topic. However, I’d like to keep the blog posts on the shortish side. Thoughts?

Next to Nothing

Well, the lack of interesting weather to write about has lasted so long that it is becoming interesting. How’s that for a contradictory sentence? It has been so dry here over the past month that my CoCoRaHS gauge has become one of the driest gauges in the country. With about 0.5 inches of rain, my gauge is the driest one on the whole East Coast and the second-driest gauge east of the Mississippi! Only a gauge in Toledo, OH is drier, with 0.47 inches of rain.

Rounds of thunderstorms have narrowly missed here, going to the northwest and southeast. Hurricane Arthur missed me to the east earlier in July. Some gauges not far away have seen 8-11 inches of rain, adding insult to injury. Here’s a graphic showing the rain hole in Central Virginia.

Courtesy of NWS Wakefield.

Courtesy of NWS Wakefield.

What is to blame for this dry stretch? A lot of it is just the nature of erratic summer rainfall. Thunderstorms are short-lived and highly variable. This summer has just been a particularly extreme example of thunderstorms forming over the same places, separating the “haves” from the “have-nots”. But the overall weather pattern can take some blame as well. With a ridge of high pressure over the West and a trough of low pressure over Quebec, dry northwest flow tends to set up in the Mid-Atlantic. This has been a common weather pattern this summer. In this pattern, air coming into the area comes from the central U.S., which is dry compared to air coming from the Gulf or the Atlantic. Also, as the flow goes over the Appalachians, it tends to sink and warm on the lee side. This tends to lower the relative humidity somewhat near the surface. Without a deep moisture source, thunderstorms are less common (but still do occur) and tend to drop less rainfall.

Summer Sadness

While the blinding sun cooked the lowly Piedmont with T/Td spreads of 97/77 and heat indices around 105, one weather enthusiast grew excited about the potential for afternoon storms to cool the parched earth. As CAPE values exceeded 3000, and as the aforementioned daytime heating steepened near-surface lapse rates to dry adiabatic levels, this intrepid, hopeful soul watched puffy cumulus clouds fill the afternoon sky. Storm Prediction Center watch boxes filled the news feeds and spirits were high as the lee trough sharpened. Just then, rumors started to spread about slight capping inversions in the mid levels, and, at once, the cumulus clouds withered and died just as the grass was doing in the summer heat. Bitterness and frustration began to seep out as beads of sweat do in a sauna, not unlike the weather conditions of the afternoon. Fists were shaken at the empty promises of far-away convective outflow boundaries over the mountain foothills, as the sun began to set in a now-sunny sky. The Second of July held such potential as magnificent RAP forecast soundings illustrated, but this weather lover will have to settle for the fleeting greeting of much-needed rainfall from the supposed rendezvous of a cold front and the distant Arthur making its way out to sea.

In other news, I have spent a month volunteering at my local National Weather Service office. I promise that those experiences will be compiled into written form and shared here in the near future.

Screen Shot 2014-07-02 at 1.24.56 PM

A promising forecast sounding (from a short-range weather model called the RAP) only results in sun-bathed convective heartbreak.

Thunderstorm Time Lapse

I am always interested in time-lapse photography, and I got an unexpected chance to capture some thunderstorms yesterday! I was just milling around at home, and decided to set up my camera when I saw some developing cumulus clouds to the east. Five hours later, I had gotten a really great series of transient thunderstorms!

 

The first 20 seconds of the video are pretty boring, but then the thunderstorms really start to get going. It was hard to guess where they would form, so I kept moving the camera in the middle of the video. Right at the end, there is a faint rainbow along the right side of the video (but it’s mostly off-screen to the right).

Technical weather discussion begins here (continue reading at your own risk):

What is really happening in this time lapse video? As long as the summertime airmass is sufficiently unstable, meaning that air forced upward will want to continue rising on its own (given several limiting conditions/factors, such as density differences), thunderstorms are likely to form in the mid-afternoon. These types of storms are very common, and are not usually severe (generally no tornadoes, hail, or damaging winds), although they can still be hazardous to people doing outdoor activities. Given a lot of sunshine and warm temperatures in the low 90s like we had yesterday, this was an ideal day for this to occur. During the first 20 seconds of the video, plumes of air heated by the early summer sun are rising, condensing into tiny liquid water droplets, and forming puffy cumulus clouds. Interestingly, all the air condenses at about the same level in the atmosphere. This is called the Lifting Condensation Level, or LCL, and is found at the flat base of the cumulus clouds (notice that this level remains constant through the video).

However, there is another important level in the atmosphere called the LFC, or Level of Free Convection. Why is this important? Any plumes of warm air that bubble up below the LFC tend to not have enough energy to keep rising and form thunderstorms. They sink back down. However, clouds that do rise above the LFC tend to keep rising on their own. All the cumulus clouds that form and decay during the first 20 seconds of the video don’t rise above the LFC. However, the cloud to the far right around the 22-second mark has enough energy and momentum to surpass the LFC and keep rising. It forms a thunderstorm. A number of cumulus clouds later in the video rise above the LFC as well, forming other thunderstorms.

But will the air parcels in the thunderstorm keep rising forever? No. At a certain level, air parcels in a thunderstorm will lose momentum and stop rising. Due to differences in density caused by the difference between the temperature of the rising air parcels compared with the temperature of the surrounding environment, thunderstorms will not grow above a certain height called the Equilibrium Level (EL). Here, air parcels have neither an inclination to rise or sink, and are content to stay at the top of the thunderstorm. They slowly spread out like a pancake, in an area called the anvil of a thunderstorm (looks like an actual anvil), which can be seen in the thunderstorm at right around 0:30.

Why do thunderstorms form in the first place? This is a matter of instability. When the sun is out, it is only able to warm the Earth’s surface (and, by extension, a small layer of atmosphere near the surface). This leaves air aloft, 1000 feet above the surface and higher, a good deal cooler than the warm surface. Surface air parcels want to rise up and cool off in this situation (general definition of instability). One of the most common ways this happens is through thunderstorm formation. Due to complicated issues of thermodynamics (the transfer of heat energy), I won’t elaborate too much. What I will say is that air parcels that rise up in a storm and form rain are able to take heat from the surface and redistribute it into the upper atmosphere, decreasing the temperature imbalance formed by the sun. Paradoxical. You can (and rightfully should) blame the sun for stormy afternoons. It is the culprit.

In summary, what you see in the time lapse video are plumes of air that are too warm to stay put at the surface. They rise and form thunderstorms, trying the bring the atmosphere back into balance. Weather is the resulting dance of the atmosphere, trying to regain balance from imbalances caused by the sun. Neat stuff!