The List of Tornado Emergencies

Posted by pmarshwx on 16 Nov 2011 | 3 comments

I’ve gone ahead and put together a list of all the tornado emergency occurrences…sort of.

The tornado emergency is a non-standard product that can be issued in several ways. This makes searching for the first issuance of a tornado emergency a bit of a programming challenge. Furthermore, a tornado emergency doesn’t have a defined start and end time. For my purposes, I will ultimately define the tornado emergency start time to be the time of the first issuance of a tornado emergency (within the framework of a single tornado warning). Ultimately, I will define the tornado emergency end time to be the end of original tornado warning. However, parsing through all of this text and ensuring the correct start and end times is a non-trivial task. Furthermore, identifying the location of the tornado emergency is difficult as it is sometimes listed as a county, a metropolitan area, or a series of latitude and longitude points. The first and the last aren’t too hard to deal with, but trying to pin down the boundaries of a metropolitan area (such as “South Oklahoma City Metro”) is difficult. I want to be very sure that I do all of this correctly and consistently before releasing any of those results so please bear with me.

Nevertheless, people have been asking for the list of tornado emergencies and so I’ve put together the following chronological list. It contains the issuing WFO, along with the start and end times of the tornado warning that encapsulates the tornado emergency. Again, the times listed are those of the parent tornado warning — not those of the tornado emergencies.

The format of the list (which can be found by clicking on the box below) is:

WFO: Issuing Time – Ending Time (Duration in minutes)

Tornado Emergencies Sans 2011

Posted by pmarshwx on 15 Nov 2011 | 0 comments

Probably the most often asked question of the last 24 hours has been, “Can you redo the WFO counts without including 2011?” So, here are the WFO counts sans 2011. The top three have changed slightly

1. BMX (Birmingham, AL)
2. MEG (Memphis, TN)
3. JAN (Jackson, MS)

There were 83 tornado emergencies between 1999 and the end of 2010…

More graphics to come…

Data Mining Tornado Emergencies

Posted by pmarshwx on 14 Nov 2011 | 10 comments

Last night I posted a call for help from fellow meteorologists and weather nerds to help me acquire the tornado emergencies that I was missing. Wow! Thanks to the help of Jason Kaiser, Daryl Herzmann from Iowa State, and Rick Smith from National Weather Service (NWS) forecast office Norman, I now believe I have all tornado emergencies in my possession! Now the fun part of analyzing them begins! Since many people are already aware of my project, I decided to go ahead and post two quick graphics that I think will be of interest.

First, a bit about my method. For this analysis I treat the tornado warning and all subsequent severe weather statements associated with the tornado warning as a single episode. Since a tornado emergency can be issued in the text of either a tornado warning or a severe weather statement, all tornado emergencies issued within a single episode is consider a single tornado emergency. Consider the following scenarios:

Scenario 1: A tornado warning is issued for 2 counties and does not contain the tornado emergency text. Subsequently 4 severe weather statements are issued. The second severe weather statement contains the tornado emergency language for county A but not county B. The fourth severe weather statement contains the tornado emergency for county B but not county A. How many tornado emergencies will this count as?

Using my definition, even though 2 tornado emergencies were technically issued, they are both contained within a single tornado warning and thus this is treated as a single tornado emergency.

Scenario 2: A tornado warning is issued for county A and does not contain the tornado emergency text. Subsequently 2 severe weather statements are issued. The second severe weather statement contains the tornado emergency language for county A. As the tornado moves into county B, the NWS issues a new tornado warning, without the tornado emergency language, for county B. Subsequently, the NWS issues three severe weather statements for county B, all three containing the tornado emergency language. How many tornado emergencies will this count as?

Using my definition, even though 4 tornado emergencies were technically issued, they are all contained within the framework of only two tornado warnings. Thus this is treated as two tornado emergencies — even though this is for the same tornado.

Scenario 3: A tornado warning is issued for county A and does contain the tornado emergency text. Subsequently 2 severe weather statements are issued, both of which contain the tornado emergency language. How many tornado emergencies will this count as?

Using my definition, even though 3 tornado emergencies were technically issued, they are all contained within the framework of a single tornado warning. Thus this is treated as one tornado emergency.

Does that make sense?

With that said, there have been 143 distinct tornado emergencies issued since the first one on 3 May 1999 for south Oklahoma City, OK. The chart below breaks them down into yearly counts:

Examining tornado emergencies by NWS forecast office, the top three are

1. BMX (Birmingham, AL)
2. HUN (Huntsville, AL)
3. JAN (Jackson, MS)

This might be a bit surprising to many who typically think of “tornado alley” as being in the central United States. Unfortunately, or fortunately, you decide, many things go into the decision to issue tornado emergencies. Some of these things include population potentially impacted and local office policies. Remember, the tornado emergency is not a formal product. It wasn’t until the last year or two that local forecast offices has official guidance in place. Bottom line, not every office uses tornado emergencies. (Also, keep in mind the magnitude of the 27 April 2011 tornado outbreak and where that was located! However, to be fair, I will say that all of the top three offices had issued tornado emergencies prior to 27 April 2011.)

The rest can be found in the chart below:

In the coming days and weeks I will be doing more analysis on tornado emergencies and will post findings as they are completed. If there is something you would like to see, leave me a comment and let me know. If I don’t already have plans to examine your request, I’ll add it to my list!

The Elusive Tornado Emergency Product

Posted by pmarshwx on 13 Nov 2011 | 5 comments

In light of this year’s extremely violent tornadoes and the reaction to them amongst the meteorological, emergency management, and social science communities, I’ve spent a lot of time thinking about the National Weather Service’s (NWS) practice of issuing tornado emergencies. For those who don’t know, this product is, in theory, designed to serve as a “more severe” tornado warning. Essentially a tornado emergency is nothing more than a regular tornado warning with a variant of the phrase, “This is a tornado emergency,” contained somewhere in the text. This phrase could be contained somewhere in the initial tornado warning or in a follow-up statement known as a severe weather statement.

Over the last few days I have been working on putting together a collection of all tornado emergencies ever issued. The first one was issued on 3 May 1999, as a severe weather statement, as the Bridge Creek F5 tornado threatened downtown Oklahoma City. Since then this product has been issued over 100 times with varying success. Much like the success of the tornado emergency product, I have had varying levels of success in tracking down all the products ever issued. So far I am fairly confident that I have collected all of the tornado emergency statements since 2005. Unfortunately I have run into a problem with tornado emergencies prior to 2005. The problem stems from the fact that the, “This is a tornado emergency,” tagline can be placed in one of several NWS text products. All initial tornado warning statements that contained this tagline are archived and I am fairly confident I’ve retrieved them all. However, obtaining severe weather statements prior to 2005 have proven elusive. (The exception to this is the severe weather statements from the Fort Worth, TX office on 28 March 2000 when a tornado emergency was issued for downtown Fort Worth, which I have found.) This is where you, the amazing people of the Internet, can help. If you are in possession of, or know of, a tornado emergency prior to 2005 that is not listed on my Tornado Emergency page, please contact me as soon as possible.

In the coming days and weeks I will be updating the Tornado Emergency page with a listing of all known tornado emergencies and eventually will provide links to all of the text products and the verification.

7 November 2011 Tornadoes

Posted by pmarshwx on 7 Nov 2011 | 0 comments

The first tornado of the day is ongoing across portions of southwest Oklahoma. The tornado vortex signature (TVS) is located just to the northeast of Tipton, where the brighter reds and greens are side-by-side. Additionally, I should point out that the Oklahoma Mesonet has lost communication with the Tipton Mesonet station. With visual confirmation of a tornado in the vicinity, this would seem to suggest the tornado moved very close to, if not hitting, the Tipton Mesonet station. This would not be the first tornado to hit an Oklahoma Mesonet station this year. Back on 24 May 2011, the El Reno, OK EF-5 tornado moved close enough to the El Reno Mesonet station that debris wrapped around the Mesonet’s observing site. The strongest measured wind gust in Oklahoma history was recorded by the El Reno Mesonet station during the tornado’s passage.

Don’t Mock the Meteorologist

Posted by pmarshwx on 29 Aug 2011 | 4 comments

Meteorologists all across the country are having questions today regarding the perceived over-hyping of Hurricane Irene. Leaving aside the discussion about whether or not Irene was over-hyped, and who might actually be to blame (spoiler-alert: It’s not the meteorologists…), comedian Dean Obeidallah offers a defense of meteorologists in his opinion piece titled “Don’t Mock the Weatherguy”

In short, Mr. Obeidallah offers this warning, “If we continue to mock these heroic weatherpeople who try to make our lives in a challenging world a little better, then don’t be surprised when, one day, we hear them collectively announce, ‘Enough!’” and leave the population “…like cavemen to predict weather based on the sounds of insects and our swollen feet.”

Meteorological Detective Work: Using All Your Tools

Posted by pmarshwx on 27 Aug 2011 | 2 comments

Tropical cyclones are giant, yet complex, heat engines driven by the release of latent heat. In a simplified context, here is how this heat engine works:

• Thunderstorms develop over the warm tropical waters in an area of weak vertical wind shear. This results in thunderstorm updrafts being nearly 100% vertical.
• As thunderstorms continue to develop, latent heat is released in the middle troposphere. As a result of this mid-tropospheric warming, updrafts become stronger.
• Because air is rising faster than it is being replaced at the surface, the pressure at the surface decreases and a surface low-pressure develops.
• As a consequence of the developing surface low-pressure, thunderstorms begin to congeal and rotate around a central point. Additionally, air at the surface begins to converge into the center of the low-pressure.
• The increased surface convergence results in additional rising motion, meaning more thunderstorms, more latent heating, and further decrease in pressure.

Throughout all of this, the center of the tropical cyclone is located at the same horizontal location as a function of height. This is often referred to as a “vertically stacked cyclone”.

The processes described above continue until a balance is achieved, or something changes in the environment. Some negative environmental changes are cooler water temperatures (resulting in cooler, drier air being lifted), landfall, or an increase in shear. The reason an increase in shear is bad is because it tilts thunderstorm updrafts which acts to weaken the updrafts, in turn weakening the amount of latent heating.

The environment around Hurricane Irene has changed completely from a few days ago. Irene moved over land, is moving into cooler waters, and is experiencing an increase in vertical wind shear. How can I tell the latter? From utilizing the radial velocity from area Doppler radars.

In a radial velocity image, the wind is either toward or away from a point (in this case the point is the Doppler radar). In the image below the doppler radar is the black dot in the center of the image. Pixels that are green to blue in color depict air that is moving directly toward the radar with green pixels indicating slower motion than blue. Pixels that are red to orange in color depict air that is moving directly away from the radar with red pixels indicating slower motion than orange. Pixels that are grey in color indicate air that has no component of motion toward the radar. This does not mean that the air is not moving!. It simply means that the air is not moving toward the radar. It might be moving very quickly, but is completely parallel perpendicular to the radar beam! Utilizing this fact, the giant grey “S” like shape down the middle of the image means that the wind is predominantly parallel perpendicular to the radar beam at that location. The black arrows indicate the wind direction along the grey “S” like shape.

One other fact to remember about radar interpretation is that because the earth is curved, the radar beam actually increases in height as it moves away from the radar itself. Thus in the image below, areas near the periphery of the image are at a higher altitude than areas near the center. Combining this fact with the wind directions from the black arrows, we can infer that the wind is changing direction from east-northeast at the surface to almost due south at some higher altitude.

Now, let’s think back to the heat engine process described above. If the tropical cyclone is “vertically stacked”, and we assume the wind is cyclostrophic (meaning it is perfectly circular) about the center of the tropical cyclone (which is a good first order approximation), the wind would be in the same direction no matter what height we examined! If we looked at a radial velocity image, the grey “line” would be a straight! This is not the case with Irene. In fact, using the cyclostrophic balance, we can determine the approximate tilt with height of the center of Irene. This is denoted by the giant “L” on the image above. (The short arrows between “L” locations indicates the path from surface to higher altitudes.)

This tilt with height indicates that Irene will most likely not strengthen (at least not significantly) as it moves back over the ocean. Furthermore, this tilt with height probably indicates that Irene is undergoing a transition from a tropical cyclone to an extra-tropical cyclone. However, discussion of the differences in the types of cyclone and the transition process will be left to a future blog post.