Explaining Vague Meteorological Terminology

When I issue a weather forecast, I look at the computer models, take current atmospheric observations into account, and put it into terms that the common person would read and understand. But, something tonight made me ask, do people really understand …. like, REALLY understand what we’re conveying in our forecast???

One of the Pittsburgh sports bloggers I follow on Twitter tweeted this earlier tonight,

“I also still don’t get the difference between partly cloudy and mostly sunny. Same thing to me. So if it is partly cloudy does that mean the weather guy is in a pessimistic mood? Or maybe the weather guy likes clouds. Who knows.”

Since one day I’ll probably be that weather guy who “likes clouds,” I figured I’d go to the handy-dandy NOAA National Weather Service Glossary to find out the exact definitions of this terminology.

In general, the term “cloudy” in a meteorological sense relates to what is known as opaque sky cover.This term refers to clouds not allowing the radiant energy from the sun to reach its maximum potential. Or more simply, clouds which prevent us, on the surface of the earth, from seeing anything above it.

Now that I probably confused you even more, let’s just quote those professionals at NOAA for the official definitions:

Partly Cloudy

Between 3/8 and 5/8 of the sky is covered by clouds.

Partly Sunny

Between 3/8 and 5/8 of the sky is covered by clouds. The term “Partly Sunny” is used only during daylight hours.

Mostly Clear

When the 1/8 to 1/4 of the sky is covered by with opaque (not transparent) clouds. Sometimes referred to as Mostly Sunny if this condition is present during daylight hours.

Mostly Cloudy

When the 3/4 to 7/8 of the sky is covered by with opaque (not transparent) clouds. Same as Considerable Cloudiness.

Mostly Sunny

When the 1/8th to 1/4 of the sky is covered by with opaque (not transparent) clouds Same as Mostly Clear, except only applicable during daylight hours.

Now that we have all the real definitions, you can tell a lot of it is time of day, where clear refers to nighttime and sunny refers to daytime. There IS a difference between partly and mostly and there is a lot of very specific criteria as you can see. However, we come to the conclusion that the tweet from this evening might just be true. Whatever mood the meteorologist is in that evening may truly be the only difference between your “partly cloudy” and “partly sunny” forecast for the next day.  But now you know exactly what they mean!!!!!!

Location. Location. Location!

What do the words “location, location, location” mean to you? For many people, this is the old slogan from Disney. For meteorologists in the last 24 hours over the eastern part of the country, this was critical to the weather conditions for the day Monday.

As you are all aware, a winter storm warning was up for northeastern Ohio last night, as the threat of a large accumulation of snow worried local residents. Since trees have already begun blooming, plants are now growing, and spring is in full swing, the threat of heavy and wet snow could have proved damaging. The ingredients were all there. The jet stream had pushed south allowing for below average temperatures to filter into the area. A low pressure area was deepening and working up the eastern seaboard. One thing was missing on Monday in northeast Ohio and western Pennsylvania though – precipitation. What was the problem???

Location, location, location!

Call your attention to the “L” just off the Jersey coast. These were the observations early this morning. That “L” is the center of the low pressure responsible for a deluge of rain up the east coast, and yes quite a bit of snow across parts of the interior northeast from southern New York state through the mountains of central Pennsylvania. The counterclockwise motion of low pressure systems in the northern hemisphere allowed the cold air to wrap around the low and push it southward into these locations.

In a report from Wunderground, some snow totals from today as of 7pm were: 10″ in Newfield, NY; 13.6″ in Laurel Summit, PA; 11″ in Sylvania, PA; 5″ in Aurora, WV; and 5″ in Keysers Ridge, MD.

If the center of the low pressure would have been where the models forecast it Saturday night, these snowfall totals could have easily been over eastern Ohio and western PA. As for the rest of the night, as the low continues to progress away from the area, there is still some moisture available for some lake-effect rain or snow showers to impact the area. In fact, as of 835pm, a band of light precip was extending from Ashtabula into northern Trumbull counties in Ohio and Erie and Crawford counties in northwest PA. Meadville, PA in Crawford county was reporting light snow and 34 degrees at 8pm. Even if this band does make it into the Youngstown area, it won’t be a problem.

Also, winds will continue to subside as the low moves away. It will remain breezy through Tuesday afternoon, but nowhere near as windy as Monday. We may see gusts in the 20 to 30mph range the first half of the day Tuesday.

Whether you were excited about getting snow and upset the system was farther east than it could have been, or were relieved because no snow occurred today, I want you to remember one thing: location, location, location! It makes a big difference in meteorology!

How Youngstown Escaped the Severe Weather of March 2, 2012

There are some days meteorologists never forget, and March 2, 2012 will definitely be added to that list. While many tornado surveys are still being completed, I’d like to discuss how it all happened, who was affected, and in the case of us here in Youngstown, how we were spared.

On Thursday afternoon, I released this Facebook status: “Warning you guys now, I will be talking about the weather A LOT in the next 24-30 hrs. Thought the system that brought all the tornadoes and severe weather yesterday across the country was bad???? Tomorrow may be awful.”

This was just one of those tornado outbreaks severe weather experts and meteorologists alike knew couldn’t be avoided. It was a textbook situation: a low pressure system and trailing cold front were moving out of the Plains underneath a strong upper level jet stream. A warm front developed and moved north through Illinois, Missouri, and Indiana allowing a surge of warm moist air from the above average sea-surface temperatures in the Gulf of Mexico to fill into the region. The deep low pressure in the upper levels of the atmosphere allowed for increased rotation and all of these ingredients worked together to create what will most likely be the largest March tornado outbreak this country has ever seen. Forecasts were given quite a few days in advance, and this most likely saved “countless lives” in a report issued by USA Today.

The Weather Channel’s Dr. Greg Forbes puts together in graphic form how all the ingredients came together March 2, 2012.

By the end of the day, tornadoes had affected 10 states – from Indiana and Kentucky, to Virginia and Georgia. Perhaps the most devastating tornado of the day affected Henryville, Indiana. This is where the now “iconic” EF-4 tornado tore up an entire community. This tornado was estimated to have winds upwards of 175 mph. As of Monday night, 45 tornadoes have been confirmed in a report from Justin Kenney from NOAA. This number is expected to increase as more confirmations are reported after NWS groups continue to survey damages and validate original reports from Friday. Of these 42 – Indiana had 3, Virginia 1, North Carolina 2, South Carolina 1, Ohio 6, West Virginia 2, Kentucky 9, Tennessee 8, Alabama 7, Mississippi 1, and 5 in Georgia. The pictures at the end of the post just sample some of what these disasters are capable of.

Just how lucky did we get in the Mahoning Valley? 6 total tornadoes were reported in Ohio, with 3 deaths thus far in the state. These tornadoes were in the extreme southwestern part of the state. Severe wind and hail reports also littered extreme southwest Ohio. A line of heavy rain and some embedded thunder and lightning affected our region Friday night, and yes this was the same system that brought disaster to so many communities. While the threat for tornadoes was never forecast to be high for us, the forecast did call for severe thunderstorms with damaging winds being the main threat. The warm front, which enhanced the moisture in southern Ohio ahead of the cold front, was a lot slower than forecast and made it through the region just before the cold front did. This was extremely fortunate for us in that the ingredients never made it this far north.

This graphic from TWC shows the warm front (in red) not quite making it into the Mahoning Valley at the time the most unstable conditions were present. This set-up was responsible for deadly tornadoes in southern Ohio, Indiana, and other parts of the Ohio and Tennessee Valleys.

This tornado outbreak does show, however, that EVERY area in the country can experience a deadly day of tornadoes if the conditions come together. We are just now entering the prime tornado season. There is no doubt extended forecasts saved lives, and it is extremely important to follow local NWS offices when severe weather strikes. Regardless, over 35 people have been killed in this outbreak, including a toddler who died after being found in a field in Indiana amongst her whole family. (ABC News Story about Angel Babcock) Here in the Mahoning Valley, we were spared. We may not get so lucky next time, so it is important to always stay up on the latest forecasts during severe weather season.

Just a few pictures from Friday’s Deadly Outbreak

Henryville, IN (C) ChicagoTribune.com

School bus taken off its foundation in Henryville, IN © CBS

Man &  his pooch even though he lost everything else – W. Liberty, KY © David Mixner

Tornado damage in Meridianville, AL © The Huntsville Times

Meteorology Explained: Types of Winter Precipitation

I told you I’d save it for a sunny day, so while we enjoy a rare weather phenomena today (yes, for northeast Ohio, I’m talking about the sun) I’d like to write about a topic that gets a lot of attention: the meteorology behind the different types of winter precipitation.

As I have said many times before, meteorology not only deals with conditions at earth’s surface, but also since the atmosphere is three-dimensional, deals with conditions all the way up through the troposphere. The types of precipitation: rain, snow, sleet, and freezing rain, all depend on the “thermal profile” of the troposphere. The diagram below shows the exact meaning of this.

Photo Courtesy Steve Cross

Okay, so what does this all mean? As you can tell, cold air needs to be present in the atmosphere for moisture to be present. Most precipitation occurs from a clash of a warm and cool (sometimes even cold) air mass. From the diagram, you can see at the top of the troposphere it is all snow. (There is another process which uses rain without the development of snow first [called the supercooled warm rain process] which I’m not going to go into for simplicity’s sake). This is because as you ascend in the troposphere, the temperature decreases. However, when a temperature inversion occurs, a layer of warm air invades the lower atmosphere. This inversion can be caused by a warm front, but in general this means that while you ascend in the troposphere it gets warmer before it gets colder. This is the area in red shading in our diagram. The type of precipitation which forms depends on exactly how thick this layer of warm air is, and is why it is extremely difficult to forecast some winter storms.

Rain occurs when the thermal profile is all warm air in the lower atmosphere. This is depicted in the farthest right part of the diagram.

Moving left, our next type of precip is freezing rain. Freezing rain is snow which falls through the temperature inversion and melts the snow to become rain. However, since right at the surface temperatures are 32 degrees F or below, these rain particles freeze on contact and is known of as freezing rain. You can see now why this is very difficult to predict. Meteorologists have a map which helps attempt to predict ice events. It is the 850 millibar temperature map, which gives the temperature in the lower levels of the atmosphere. However, as you can expect, one degree makes a lot of difference as to what type of precipitation occurs, so forecasters are walking a fine-line with this type of weather.

Sleet then, occurs with a larger pocket of cold air at the surface and doesn’t spend as much time in the warm air. This means that, as the snow falls into the warm air it starts melting. However, since it goes back into the cold air more quickly than the freezing rain did, it isn’t entirely melted. It re-freezes when it comes back into the cold air and often bounces off the ground. This then, doesn’t freeze on contact and is less threatening than freezing rain.

Snow, of course, is when the entire region in the lower troposphere is cold and no melting takes place. The snowflake remains a snowflake when reaching the surface.

No matter what type of wintry precipitation falls, driving is always hazardous when the temperature drops. When we forecast any type of precipitation, you should take extra caution while outdoors. Freezing rain is the most dangerous, as when it accumulates the ice can cause extreme problems. Sleet and snow accumulations, as you well know, can do the same as can rain. I can go into greater science behind the types of precipitation, but this I believe will help the common person understand the basic science behind the different types of precipitation. If you have any questions, please let me know!

Tumultuous Twisters create Deadly 2011

“Everything was off the charts. Everything. The chance for rotating storms; off the charts. Chance for Instability; off the charts. The chance that we would have long track tornadoes; off the charts. Everything came together just perfectly.” These words from The Weather Channel’s Jim Cantore describe how 2011  became the year which tornadoes were one of the biggest weather stories. 2011 featured many devastating tornado outbreaks and one single tornado that changed the lives of a community, and possibly the entire country.

The first outbreak of tornadoes occurred a few weeks into April and lasted three days from April 14 to 16. States such as Oklahoma, Arkansas, Mississippi and Alabama were affected amongst others. However, the final day of the outbreak was the worst as North Carolina got in on the action. By the time this outbreak was over, roughly 150 tornadoes had affected 15 states and 38 people were killed. This outbreak was enhanced by the sharp contrasts in temperature between the Midwest and the southeast US. At the time of these tornadoes, the mountains of Colorado were experiencing blizzard conditions. However, what took place in late April was caused by more than just a temperature gradient.

Last winter was a moderate La Nina winter. History has shown that after a La Nina winter, the spring following typically sees an increase in severe weather farther east than the typical “tornado alley.” With La Nina, the ocean waters in the Pacific are cooler farther east. The waters of the Gulf of Mexico are actually warmer. This warmer water brings more moisture which brings greater instability into the southeastern United States. This set up allowed for one of the season’s first major outbreaks in Alabama at the end of April. Meteorologist Mike Bettes put it this way when discussing the outbreak: “It just meant one violent tornado after another after another. Your head was spinning with all the tornado warnings. You couldn’t even keep up with it.” Twelve tornadoes were rated EF-4 or EF-5. Cantore remarked, ““EF-4s and EF-5s make up about 5 percent of all tornadoes out there, just to show you how rare they are, and to have so many…that’s why we lost so many people.” The tornado in Tuscaloosa, AL was rated an EF-4 with winds estimated around 190 mph. According to The Weather Channel’s severe weather expert Dr. Greg Forbes, some of the tornadoes that day were more than one mile in length and traveled around 100 miles. In this one day, 210 people were killed and 1700 injured in Alabama with roughly  50 tornadoes. In the 21st Century, meteorologists have a lot of tools at their hands to prevent a large number of people from dying in a natural disaster. As storm-chaser Juston Drake reports, it’s not all on the meteorologists, people have to pay attention to. Drake said “because of the hills and trees in the southeastern United States, you can’t see a tornado coming toward you at 60 mph.” Some people just didn’t realize these tornadoes were on top of them until it was too late, and they had nowhere to take shelter. Following the tornadoes, it took days and weeks to assess the damage. Immediately after, it took 4 hours to get people out of their apartments. One group of people had to take shelter under a tanning bed in Georgia. They all survived. Another surviving family reported as they were in their shelter, “you can the house just ripping apart over us.”

By the end of the month, April had seen 677 tornadoes. This number broke the record for the most active month ever for tornadoes. May was much quieter. The only problem in May was that one single tornado, on May 22, would be more than enough than anyone wanted to see.

The Joplin, Missouri tornado may be one of the most prolific weather events of 2011 and was one of the deadliest single tornadoes in American history. At 541pm, a multi-vortex tornado became an EF-5 with winds of over 200 mph. Debris was flying as high as 18,000 feet. Bettes said, “could you imagine flying in a plane and seeing a tree go by?” Cantore remarked, “cars [were] crumpled like you would take an aluminum can and crumple it up.” Bettes and his crew were the first media to assemble on the scene after the tornado. He remarked, “we witnessed things we didn’t want to witness. It was chaos…the saddest moment of my career.” While not there, Cantore remembered other instances as he said “when you see dead bodies and smell death it’s a horrible thing.” There were many stories of heroism that came from Joplin. A young couple was in a bathtub. The husband, 31 yrs old, died from a piece of flying debris while shielding his wife. Will Norton, who is well known in the YouTube community, was killed driving home from his high school graduation. One of the most vivid images from the tornado was the St John’s Medical Center where almost all the windows were blown out. The tornado hit the building head on, and patients had to be transported to nearby buildings. This single tornado caused roughly 3 billion dollars in damages. It killed around 150 people, making it the deadliest tornado the US had seen in over 60 years. Dr. Forbes states, “the death toll was like we saw back in 1930s and 1940s, when there were no tornado warnings, no watches, no forecasts. In this day and age unbelievable that we had so many fatalities.”

It wasn’t simply the southeast and tornado alley which saw tornadoes in 2011. While another tornado outbreak occurred in Oklahoma just after the Joplin tornado, the next big story wasn’t in a typical location. Deadly tornadoes occurred as far to the northeast as North Springfield, Massachusetts. This was the first tornado in Massachusetts since 1956, and killed 4 people.

These are just some accounts of the tornadoes of 2011. By the end of the year, communities from California to the east coast had been affected in 2011 by a tornado. All in all over 15 billion dollars of damage were from these tornadoes, and a striking death toll of around 530. One survivor put it,  “if you’re alive and you got out of this, you had a miracle.” While meteorologists and public officials are working on ways to prevent years like 2011 from happening again, certain things are out of our control. Advancements are always being made to tools such as Doppler Radar, but with increased population in many of America’s big cities comes an increased risk of fatality due to tornadoes, or any natural disaster. While we have turned the page to 2012, the scars of those whose lives were affected by the tornadoes of 2011 will not soon leave them. However, rebuilding is necessary and will continue. Jim Cantore said it best, “New Orleans has come back, Tuscaloosa will come back, Joplin will come back.”

The following pictures are just a small sample of the destruction left by the tornadoes of 2011:

St. John’s Medical Center, Joplin MO

Actual Joplin tornado

Joplin, MO

Man lost entire family in Joplin tornado but 2 days later finds his cat

NC tornado April 16

Tuscaloosa, AL April 27

Arial view of Tuscaloosa, AL

4-27 radar. textbook hook echo signals tornado

Springfield, MA after 6-1 tornado

MA Radar 6-1 (looks like it should be Midwest)

Oklahoma 5-24(Note: Photos courtesy of Google Images. Each have their own copyright.  Source of statistical information in this post was “2011: The Year of the Tornado” from The Weather Channel)

Is La Nina to Blame for Warm November and December?

A friend of mine read a discussion from NOAA’s Climate Prediction Center regarding the La Nina pattern that has been intensifying over the past month. She asked me if there was any correlation between this and the unusually warm November and December we have experienced in the Mahoning Valley. I figured since I did some research for her, I would let you all in on what I found out.

There is no doubt that we are in a La Nina pattern. This means that unusually strong trade winds in the Pacific Ocean have displaced the cooler waters of the ocean farther east than under normal conditions. While not completely understood as to why, there is a relationship between these conditions and weather patterns in the northern Hemisphere.

Figure credit: NOAA       

This figure is a look at the departure from normal sea surface temperatures (SST) in the Pacific as of November 30, 2011. Note that the eastern Pacific is in a lot of blue, which signifies below average. These averages are based on a time period from 1971 to 2000. What long-term forecasters and climatologists pay attention to during these events is how history has played out when such events have taken place. For example, recent La Nina years were 2007, 1999, 1995, and 1988. The strength of the La Nina differs from year to year depending on just how cold the waters get in the Pacific. 2007 and ’99 were “moderate” strength while ’88 was strong, and thus the affects are a little more extreme. I’m not going to go into much more detail on this, but this season the La Nina is weak to moderate.

Looking back at these La Nina years (and there are more, but these are just a sample), we in the Great Lakes region tend to see more precipitation than normal. We have noticed that already, with the large amounts of rain and flooding we have seen in recent weeks. In the 2007 La Nina pattern, we had the 3rd snowiest and also 7th wettest January on record. Why have we seen a lot of rain and not snow? This actually does not have to do with the La Nina but simply the upper air pattern. The extreme cold air in Canada has pretty much been trapped there, and the jet stream (a large wind current in the upper atmosphere) has not dipped to the south to allow the cold air advection to move southward.

Will the rest of winter be as warm? Will we remain without a lot of snow and see a lot of rain? We will remain under La Nina most likely through the beginning of Spring, when it is forecast to weaken. Therefore, long-term forecasts continue to favor above average precipitation and near normal temperatures. Individual storm systems and temporary upper air patterns will control the precipitation type and temperature on a day-to-day basis. The best advice I give is to be continually monitoring weather forecasts as long-term forecasts cannot predict when a large winter storm will hit. We at Ytownwx HQ will continually monitor the storms and help you to prepare, because after all – it IS winter!

I’d like to thank the Climate Prediction Center and Golden Gate Weather Services for information used in this post. For a complete look at the CPC’s discussion on this year’s La Nina pattern, click the following link:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

Meteorology Explained: Zonal vs Meridional Flow

Living in the middle latitudes, a key to meteorological forecasting is in the hands of what happens high in the atmosphere, thousands of meters up. Since it affects us a lot here in Youngstown, and will over the next week, I thought I’d do a little explaining about the two types of upper level air flows that impact our weather at the surface.

First off, why do we care what happens above earth’s surface? In the upper atmosphere, meteorologists look at the temperature of the air below a given surface. These “heights” determine if a trough or ridge is in place, and the patterns of these troughs and ridges are the two types of air flows that determine weather systems.

As you move up in the atmosphere, air pressure decreases. An average surface pressure is around 1013 millibars. In meteorology, we use many different pressure levels higher up in the atmosphere to determine the aforementioned troughs and ridges. Let’s just take an easy example and use the 500 millibar surface because that’s where about half of the atmosphere is above you and half the atmosphere is below you. However, the location of this 500 mb line differs in the atmosphere depending on the temperature below it. Since cooler air is more dense than warm air, the height of the air is lower because it takes up less room. Because cool air rises, troughs form from the rising air. On the contrary, ridges form where heights are higher due to warmer less dense air.

Now that I’ve confused the heck out of you, let’s put it into easier terms. What meteorologists love to see is a zonal flow, because it’s quieter. A zonal flow means that the upper level winds are blowing parallel to latitude lines. This creates a lack of troughs and ridges, thus allowing for a quieter surface pattern. An example of this is shown below:

On the contrary, when there is a meridional flow present, alternating troughs and ridges create multiple storm systems, and thus lead to a pattern of stormy and calm weather. Also a shift of colder and warmer temperatures are present. An example of this would be:

As you can see here, two big dips (or troughs) are affecting the US – one in the Rocky Mountains and the other in the northeast. These troughs create ridges as well. At the surface, the troughs represent storm systems and the ridge, calm weather.

How it affects you: These troughs and ridges in a meridional flow move from west to east and thus create for alternating weather in one specific location (i.e Youngstown will be clear a few days followed by cloudiness and precipitation for a few days). In the zonal flow, the lack of ridges and troughs create a calmer weather pattern. Obviously weather changes constantly and these patterns do not stay constant for a long period of time. This post was to elaborate on why our weather does change a lot, but many other factors also affect a weather forecast. However, this is one major culprit to weather forecasting and so I thought it may be interesting for you all to read since our weather really does change in the blink of an eye here in Youngstown!

I would like to thank www.theweatherprediction.com for the background information for this post. Images in this post are copyrighted from RAP Weather Forecasting global forecast weather models.