May 31: Pennsylvania’s Worst Historic Weather Day

This post was originally published on psuchase.org

Generally, severe weather season in Pennsylvania occurs later in the year than it does out in the Plains and other parts of the country, with the peak of severe weather season usually occurring in mid- to late-June, climatologically speaking. However, if there’s one day of the year when memorable damaging weather seems most common in Pennsylvania, that day would be May 31. Here’s a sample of four severe weather events that have all occurred, mostly in Western Pennsylvania, on May 31sts.

1889: Johnstown Flood

johnstownfloodToday marks the 125th anniversary of one of Pennsylvania’s most historic and notable disasters – the Johnstown flood (known locally as the Great Flood of 1889). A large storm had dumped nearly 6 to 10 inches of rain, the previous day according to the US Army Signal Corps (still responsible for a large portion of meteorological observations in the 1880s). The rain overnight was enough to cause severe localized flooding, with the Conemaugh River to already nearly overcome its banks by daybreak. Meanwhile, 14 miles upstream, local residents were concerned by the amount of water that almost overwhelming the South Fork Dam. They worked throughout the morning to try and free the clogged spillway to reduce pressure on the dam, but their best efforts were still futile and less than two hours after they abandoned their efforts, the South Fork Dam collapsed at 3:10 PM. A telegraph had been sent from the town of South Fork to Johnstown twice, trying to warn officials of the impending dam break, but these messages were ignored, as previous warnings had proven to all be false alarms.

The torrent of water, now heading downstream with flow rates approaching that of the Mississippi River, according to recent studies, rushed its way towards Johnstown, destroying houses and businesses in the towns of South Fork, East Conemaugh, and Woodvale. The flood reached Johnstown nearly an hour after the dam broke, causing catastrophic damage and creating a pile of rubble at the Stone Bridge downtown covering 30 acres and 70 feet tall. In all, 2,209 people lost their lives in the Great Flood of 1889 and the flood caused more than $17 million in damage. It was the first major disaster to be served by the newly-formed American Red Cross.

For more, check out the Johnstown Flood Museum (online and/or in person!)

Source: Wikipedia (Photo: ExplorePAHistory.com)

1985: PA’s Worst Tornado Outbreak and Only F5 Tornado

May-31-1985-United-States-Canadian-tornado-outbreakThe worst tornado outbreak to ever strike eastern Ohio and Pennsylvania occurred on May 31, 1985. A ripe environment in place throughout the day finally gave way to storms by late afternoon. The National Severe Storms Forecast Center (the precursor to today’s Storm Prediction Center) issued a tornado watch at 4:25 PM. Within half an hour, a tornado was spotted near the PA/OH border near Erie county, moving into Albion, PA, where nine people lost their lives. At 6:30 PM, a tornado touched down in Portage County, Ohio and quickly strengthened into a powerful twister. By the time it crossed into Pennsylvania near the town of Wheatland, Mercer County, it was nearly a half-mile wide F5 monster.

Tornadoes destroyed buildings and lives on a stretch from nearly Erie to Beaver, PA, and by the time all was said and done, 65 individuals had lost their lives in Pennsylvania alone. Another tornado tore across central Pennsylvania on that day, leveling more than 90,000 trees in the  Moshannon/Sproul State Forest. A debris ball was even visible on the primitive WSR-57 radar in State College with so many trees being tossed around in the air as the tornado ran a track parallel to Interstate 80 sixty-nine miles long.

For more information on this outbreak, I highly recommend the book Tornado Watch Number 211 by John G. Fuller.

Sources:  Wikipedia | Pennsylvania Highways Feature (Photo source: WCVB slideshow)

1998: A Derecho in Northern PA, Tornadoes Rock Many Other Counties Across the State

On May 31, 1998, another very unstable environment was present across Pennsylvania. With a warm front lifting northward and the jet stream present overhead, deep, strong shear was present, along with high levels of instability. An F3 tornado touched down in Somerset County and stayed on the ground for 15 miles, stretching up to half-a-mile wide at times. The tornado struck the towns of Salisbury and Pocahontas, destroying a furniture factory and house, a significant part of the $4 million total in damages. Tragically, there were 15 injuries and one fatality – a 13-year-old girl killed when a tree struck her car.

Tornado Damage in Somerset County
Tornado Damage in Somerset County

In the eastern part of the state, an F3 tornado caused more damage to many homes in Berks County. Several more weak tornadoes touched down across the state on May 31, 1998, with touchdowns recorded in Elk, Chester, Lackawanna, Luzurne, Lycoming, Montgomery, Pike, and Wyoming counties. Non-tornadic damage was severe as well, with a bow echo flattening trees and causing damage across Pennsylvania’s Northern Tier (not far from where the F4 tornado struck in 1985), leading to significant damage in Williamsport, PA as well.

Source (including photo): http://www.angelfire.com/pa/pawx/053198/053198.html

2002: Microburst Causes Fatal Damage at Pittsburgh Amusement Park

A cold front associated with a strong, mature low pressure system pressed through the Pittsburgh region on the evening of May 31, 2002. As the line crossed through Allegheny County, a microburst occurred near West Mifflin, near the amusement park Kennywood. The Whip, an 84-year-old ride at the park, collapsed when the microburst struck, killing one woman and injuring 54 others. This storm was subsequently tornado warned in Allegheny and Westmoreland counties, but no tornadoes were confirmed from this storm. Regardless, a significant amount of wind damage was reported across southwestern PA.

kennywood-radar

Remembering Tornado Researchers Tim Samaras, Paul Samaras, and Carl Young

This post was originally published on psuchase.org

Ever since I was a young boy, I have been fascinated by severe weather. Growing up, I watched several “storm chase” videotapes, as well as the movie Twister and other specials that would appear on television. I especially loved the showStorm Chasers on the Discovery Channel. It is through this passion for storms that got me to the point where I’m now webmaster for the Penn State Storm Chase Team.

Up until Friday, most knew that storm chasing was an incredibly dangerous activity, but no major losses of life had occureddirectly during a storm chase. We knew on Friday that a Weather Channel chase vehicle had been flung by a tornado far from the road, but that no major injuries had occurred. This prompted a discussion about the dangers of storm chasing on Saturday.

Then, the news of the Twistex team hit. Going to bed Saturday night, rumors were swirling that tornado research legend Tim Samaras had perished storm chasing on Friday. This news was sadly confirmed overnight. He died in the El Reno, OK Friday night alongside his son Paul and their longtime chase partner Carl Young. The rest of this post is a Storify I created to memorialize these true tornado research pioneers:

Twisted News: The Latest Tornado Outbreak and Warning for the Future

Note: This article has been minorly edited from its original form to remove some stale links and reformat some of the other media on the page.

It seems as though tornadoes just can’t stay out of the news, as of late. Cable news stations were abuzz Tuesday night and Wednesday showing the latest dramatic pictures and videos from the latest tornado outbreak, this time centered near Dallas/Fort Worth, Texas. The especially notable video from yesterday’s event was of tractor-trailers being thrown around into the air as if they were empty cardboard boxes!

There were two other interesting things to note about yesterday’s event. First, for a decently long period of time, there were two concurrent supercells on the Dallas/Fort Worth radar, both of which contained sharp hook echoes, indicative of possible tornado development.

It appears that the majority of the damage came from the eastern storm, which had a longer period of time to exist on its own before becoming absorbed into the main frontal squall (see Figure 1). The second unique feature was that the damage seemed rather well-defined to the Interstate 30 corridor. This can be seen in great detail on the Storm Prediction Center’s Filtered Storm Reports Google Maps page (Figure 2 shows a zoomed and cropped version). It’s fascinating to see the paths these storms take, which, while random, have certainly been known to follow interesting paths before.

Figure 1: A 24-hour radar loop of the Dallas, TX radar for April 3, 2012. (Source: Weather Underground)
Figure 1: A 24-hour radar loop of the Dallas, TX radar for April 3, 2012. (Source: Weather Underground)

Figure 3: NOAA SPC Filtered Storm Reports Google Maps page, showing the large number of tornado reports directly along the Interstate 30 corridor (each "T" on the map is a tornado report).
Figure 3: NOAA SPC Filtered Storm Reports Google Maps page, showing the large number of tornado reports directly along the Interstate 30 corridor (each “T” on the map is a tornado report).

An interesting article was posted on Wednesday by meteorologist Paul Douglas discussing the possibilities of an extremely tragic urban tornado in America. In fact, the article is titled “Tornado Warning: ‘One of These Days a Single Tornado Will Claim Over 1,000 American Lives'”, based on a quote by meteorologist and structural engineer Tim Marshall, which appears in the article. It’s a fascinating read, and covers many of the bases of our dramatically shifting methodology about warning the general public about tornadoes. I have observed the warning process undergo several strong transformations, really over the past two years. In preparing to write this blog post, I was reviewing an old blog post about the stage collapse at the Indiana State Fair last August and came across a powerful quote by Brian Williams of NBC News. I’ve reposted this quote below because it is very relevant to this article, as well:

The truth is the National Weather Service is so good and forecasting has become so accurate, bad weather seldom arrives these days without warning.

Source: “Protect the National Weather Service” Facebook Page

As discussed in Douglas’s article, we are now able to issue watches and warnings for nearly every severe weather situation accurately. A dramatic improvement to the warning situation occurred in 2007 when polygon-based warnings were implemented, allowing for more specific “pinpointing” of areas at direct risk for severe weather. Now that we have the warnings, the emerging issue is getting these warnings disseminated to the general public in the most effective manner. Douglas discusses several ways to stay informed with “Multiple Safety Nets” (as he called it), including NOAA Weather Radios, Local Media, and mobile notifications. The latter item is an area of interest to me, as sooner or later, everyone will have a web-enabled, GPS-capable mobile device. Email alerts are nice for now, SMS is even better, but truly, a location-aware app that can push warnings to the user as they’re issued is the key to future warning advances. The best I could find, linked directly from the article was the iMapWeather Radio app for iPhone, created by Weather Decision Technologies, Inc. The description for this app seems to address perfectly every thing I could want in this sort of application: it only warns you if your location lies directly within a watch/warning polygon, it updates your location automatically to ensure you’re always receiving the most relevant alerts for your location, and you can even save locations of friends and family to ensure they are safe as well. Those features are well worth the $9.99 price, in my opinion. Now, if only there was something of the same caliber offered for Android (my smartphone platform of choice at the moment).

While I’ll leave it up to you to read through the rest of Douglas’s article (it’s worth the time, trust me), I do want to quote one other section with a fairly “recent development” with regard to protecting lives during tornadoes: wearing helmets!

Tornado Helmets? No, it’s not getting sucked into the clouds like Dorothy in The Wizard of Oz. Nearly 90% of tornado deaths and injuries result from blunt head trauma. That’s why you want to get below grade, in a basement, if possible, to avoid a violent blender of hurtling debris. Here’s a hint: Find bike/football/hockey helmets for yourself and your kids. I know it sounds a little crazy, but anecdotal evidence suggests padded helmets can greatly lower the risk of blunt head trauma. It may look a little goofy, but then again, looking goofy may just save your life.

If you ask me, this solution sounds like it would be common sense, but it really took until about earlier this year for me to see it being used popularly by mainstream media. Hopefully this trend continues.

Finally, while we’re on to topic of tornado warnings, a new pilot program at five weather service offices in Kansas and Missouri will be implementing a tiered tornado warning system with much strong wordings in significant warnings, including such phrases as “mass devastation,” “unsurvivable” and “catastrophic”. This seems to be a logical extension of the “Tornado Emergency” text added to particularly noteworthy tornado warnings today, which is done on a more unofficial standard. This system would hopefully create universal guidelines for various “levels” of tornado warning severity. I’m all for it. Many have credited the National Weather Service’s warnings for preventing any deaths from occurring in yesterday’s outbreak in Texas. We’re at a good place with regards to tornado warnings in the United States. However, we cannot be complacent here; we must continue to improve our systems continuously. Mother Nature loves throwing curveballs.

Basic Skew-T Analysis: Snow or No Snow?

It’s been a long time since we’ve posted some new content to the site, but in honor of Leap Day, let’s leap across the country to do some real basic Skew-T analysis in central California to check out the chance for snowfall later this morning.

Note first that elevation plays a huge role in the type of precipitation for the region we’re taking a look at today. The point that I had my Skew-Ts centered around is located at an elevation of approximately 2100 feet ASL. Go a few hundred feet up in elevation, and it’ll most certainly be cold enough for snow to fall, at least in the layer directly above the surface. Go down several hundred feet and snow is much less likely to occur. As we’ll soon see, there are some very interesting divergences in the models we’re looking at here.

What we’re going to be focusing on primarily in this post is reading part of the Skew-T Log-p diagram to determine (or at least take a stab at) precipitation type. The “Skew-T” diagram is one of the most useful, but rather intimidating tools in meteorology (it’s basically a super-convenient atmospheric calculator). To read more about the Skew-T diagram, click here! Now let’s start analyzing some weather!

All of the model soundings in the diagram are centered around the point linked to above and are for 15z, or 7AM PST.

Skew-T Image Discussion
05z-ruc-skewt The RUC model is a higher-resolution model that runs every hour. What we see on this diagram from the 05z run is that the surface temperature is solidly above freezing (freezing being the line starting at 0°C on the bottom axis and moving diagonally up to the right). The temperature (and wet-bulb and dewpoint temperatures) all cut across the isotherms (lines of equal temperature) as height above the ground increases. This means the temperature cools off rather quickly as height increases. However, because the surface temperature is well above freezing and there is a fairly tall layer (from the surface to around the 875mb height) above freezing, I would say the most likely surface precipitation type based on this model would be rain.
00z-nam-skewt The NAM is a short-term forecast model which runs four times a day. This diagram was generated based on data from the 29 Feb 00z run. It is much more interesting in terms of precipitation type for several reasons. First, the surface temperature is almost spot on the freezing mark. The temperature profile is markedly different the first several hundred feet above the surface compared to the RUC output. While this model also is predicting precipitation at 15z, the temperature profile remains ever so slightly below freezing up to about the 860mb level or so (approximately 1300m above sea level) before decreasing much more rapidly with height. I would expect snow showers from a profile like this, and find this scenario to be somewhat believable.
18z-gfs-skewt The final output displayed here is from the GFS model, which is a global forecast model which also runs four times a day. Unfortunately, the latest data I was able to access while writing this article was the 18z run, which is rather outdated (in the world of weather forecasting). On this diagram, the surface temperature is just above freezing, while there is a slight warm pocket noticeable immediately above the surface. This warmer pocket (an inversion, really) contributes to more interesting frozen precipitation types. In this case, because the “warm” layer is so shower, I would be inclined to say that this diagram is indicating mostly snow falling, with some pellets of sleet mixing in, possibly.

The Skew-T diagram, no matter how useful, is only one tool in the forecaster’s toolbox. As you can see, different models can create very different scenarios for the same location at the same time. That’s part of the challenge of winter weather forecasting! If I were to make a prediction for this setup (difficult considering I am rather unfamiliar with the area), I would go with snow as the most likely precipitation type. It may mix with some rain showers (and possibly sleet, though I find that to be more unlikely). It’s important to note that the Skew-T diagram is by no means likely the easiest, nor the best, way to get a snowfall accumulation prediction. Here, we’re simply examining the profiles to get a sense of what sort of precipitation type is most likely. Perhaps we will tackle the accumulation problem in another blog post. Hopefully for now, you have gained some new appreciation as to one of the most powerful tools in meteorology – the Skew-T log-p diagram!

Thanks to Andy M. for providing today’s question!

A Summary of Blogs on the Indiana State Fair Stage Collapse

There has been much news and discussion concerning the tragic stage collapse at the Indiana State Fair near Indianapolis Saturday night. Five people were killed, with several dozen more injured when the temporary stage set up there was blown over by a severe gust of wind (among others, Henry Margusity of Accuweather believes that the wind could have been from a gustnado – a wind vortex that begins at ground level along the gust front of a thunderstorm). Indiana governor Mitch Daniels has called the event a “fluke”, which, while a common gesture of disassociating blame among the general public, has been quickly and loudly doubted by many whose professional lives involve analyzing the weather.

Meteorologists from across the nation have chimed in on many interesting topics surrounding this tragedy. It does not take very long to understand the basic meteorological principle that occurred here: a strong, sustained gust front working its way ahead of a long line of severe thunderstorms passing across the state. That, for the most part, is not the topic of their discussion. They instead are touching on such issues as reading radar data, smartphone weather data availability and “playing meteorologist” as well as some talk of emergency preparedness and who should really be monitoring the weather for these sorts of events. I’ve attempted to pull some of the best content from entries I’ve discovered below.

KIND Radar Loop from 8:00-9:06PM local time (0000z-0106z) showing the approaching gust front and storms. Image source: Brad Panovich.

We begin with some commentary by Brad Panovich Chief Meteorologist at WCNC-TV in Charlotte, NC. Brad has a detailed timeline of the event on his posting, along with many corresponding radar images like the one posted above. He does not deny the possibility of a weather-related “fluke” occurring (as these certainly can with “pulses” of strong winds from suddenly emerging/strengthening storms), but says that this was clearly not the case here. (A trained eye need only glimpse at the radar loop above to see why.) He further writes:

There was plenty of warning, if you you knew or wanted to know what was going to happen. The focus on the actual Severe Thunderstorm Warning is insignificant in my opinion. The warning was issued at 8:39pm which was 10 mins before the stage collapsed. A severe thunderstorm warning is only issued when winds are 58mph or higher or hail is 1” in diameter or larger. Problem here is you have people in an outdoor event and around a temporary structure which requires them to seek shelter at a much lower threshold. Something that should have been known by those organizing the event. One of the fatalities was a stage hand in a metal light structure running a spot light, with lightning clearly visible in the distance. Lightning alone was sufficient reason to evacuate people and since lightning was within 10 miles of the fair grounds patrons should have been seeking shelter.

He also takes issue with the quoted reliance on smartphone apps in dealing with this situation, eloquently stating that “a weather app is not a meteorologist just like WebMD is not a doctor.”

This quote was also noted by WRAL-TV (Raleigh, NC) meteorologist and weather producer Nate Johnson in his posting titled “Smarter Phones, Smarter Weather?“. His post asks the question “Does putting these tools and data in someone’s hands automatically make them credible and qualified to use those tools and interpret those data?”  (emphasis mine) to which he responds, “Clearly, the answer to that is ‘no’ — however, there’s more than enough anecdotal evidence to suggest that’s exactly what happens anyway.”

Meteorologist and author of the book “Warnings: The True Story of How Science Tamed the Weather” Mike Smith echoes Nate’s concerns that weather consumers (that is, the general public not in the meteorological field) too often take the tools they “know how to use” and try to “play meteorologist”, attempting to recreate what they watch their local TV meteorologists do. (There isa line between simply pointing at a “yellow blob” on an iPhone screen and understanding the meteorology behind it.) In fact, Mike’s “Best Practice #1″ for businesses in the path of severe weather is to “get out of the weather business.” He follows that statement with the claim that “Meteorology is a complex science and determining the safety of thousands of people is not a role for amateurs.”


It is clear that there are many forces in play when dealing with severe weather threats. For whatever reason, there was a breakdown in balancing these forces on Saturday which resulted in the untimely and unfortunate death of five fairgoers. We are at a pivotal point in this country when it comes to paying attention to the weather. After extreme weather running the gamut in not only type but also location this year, more Americans than ever are tuned into the weather. Many will try to tackle forecasting severe storms on their own, in the same “do-it-yourself” spirit they likely conduct many activities in their lives. But the weather is still a very tricky business. At this point, it is still very much better off left to professional meteorologists. As Brian Williams of NBC News reported on the situation in Indiana:

The truth is the National Weather Service is so good and forecasting has become so accurate, bad weather seldom arrives these days without warning.

Source: “Protect the National Weather Service” Facebook Page

Mike Smith reported a similar forecasting success story in the private sector, claiming “Our AccuWeather meteorologists correctly identified the situation and issued a warning for a client near the Fairgrounds that called for ’60 mph winds’ a half hour before the time the winds collapsed the stage.”

What has happened is done. Our thoughts and prayers go out to those killed in the storm and our wishes for a speedy recovery to those injured over the weekend in the Hoosier State. But as Tim Ballisty of The Weather Channel writes:

This is a teaching moment. There are lessons to be learned – the main one being we should all be weather aware especially when outdoors; taking the necessary precautions in advance of approaching severe weather. Knowledge is power. When attending an outdoor event, find out the weather forecast for the day beforehand and monitor the sky. Don’t just leave the decision making to event officials. Use your common sense and take matters into your own hands. If you don’t feel safe, do something about it. Seek safety and look after the well-being of your friends, family and others around you.

More Information

Damaging Tornado Strikes Westmoreland County

For the first time since December 2006, a tornado has touched down in Westmoreland County, PA. This was a very impressive storm which, unfortunately, caused significant damage in Hempfield Township – including the Fort Allen neighborhood which was damaged by the December ’06 twister. This very severe storm began to intensify quickly as it entered western Westmoreland County around 4:25PM on March 23, 2011. The National Weather Service in Pittsburgh observed a tornado vortex signature on Doppler radar at 4:29PM and, correspondingly, issued a tornado warning for central Westmoreland County eight minutes later at 4:37PM.

Some have argued that this was an abnormally long delay between observing the tornado on radar and issuing a warning. Do note a few items in this case, however. First and foremost, the Pittsburgh area does not see tornadic conditions all that often. While I’m sure there have been more (false alarm) tornado warnings issued since 2002, there have only been 7 dates when tornadoes were confirmed in Southwestern Pennsylvania, according to the Tribune-Review. Thus, one could argue that NWS meteorologists in the Pittsburgh office may not be as “experienced” in issuing Tornado Warnings. They also may be a more conservative office, wanting to attempt to minimize the number of false positive tornado warnings. There was also some precedence for severe weather events in Westmoreland County on Wednesday, as the entire region had been under a Tornado Watch since 1:15PM and the county had been severe thunderstorm-warned for a solid 20+ minutes before the tornado warning was issued. Finally, it is important to note that the worst of the damage occurred in Hempfield Township, right where the green arrows are in the below picture (Figure 1). The strongest radar echoes (colors on the radar) were still a few miles west of the area of greatest damage at 4:42PM, and in fact, the preliminary Storm Prediction Center tornado report was not until 4:45PM. This means residents of the Fort Allen area (and surrounding communities near Hempfield High School) had approximately 10 minutes of notice from the Tornado Warning and even more time from the Severe Thunderstorm Warning. Finally, the warnings obviously did their jobs regardless of timing, as no serious injuries were reported.

Figure 1:  4:42PM Reflectivity and Velocity Radar images (dead image link)

Four minutes later, at 4:46PM, extremely strong rotation was reported on the velocity mode of the Doppler radar. (You can read more about how velocity mode works here, but for now, know that strong values of red and green right beside each other [known as a “couplet”] are very strong indicators of a tornado.) The center of circulation, as represented by the green arrows on the radar image below (Figure 2), appears directly over west-central Hempfield Township area, right near Hempfield Area High School, which sustained significant damage in the storm – including roof damage to the auditorium and damage to the athletic fields. The numbers on the radar image correspond to the figure numbers of the other images listed below and their approximate locations. This should help to frame exactly what the tornado looked like around 4:50PM. Figure 3 really speaks to me about the potential strength of the tornado, as the twister appers to be taking on a classic “stovepipe” shape.

radar image
Figure 2: 4:42 PM Radar Velocity image with labels

Funnel Cloud from US 30
Figure 3: Route 30 West in Hempfield Township

funnel cloud, arona
Figure 4: Funnel cloud observed from Arona, PA

funnel cloud New Stanton
Figure 5: Funnel cloud observed at the UPS facility in New Stanton, PA

There were a few other very interesting observations from this storm. The first of which was the massive amount of large to “giant” hail that fell during the storm. There are numerous reports of hail at least golfball sized, causing damage to many vehicles. I have seen hundreds of photos of the hail, some of which were actually approaching baseball-sized. Figure 6 below was taken by my brother and shows the interesting cross-section of a hailstone that I’d approximate is about 1.25″ in diameter. For more details on the countless hail reports, check out the Storm Prediction Center Storm Reports page. Finally, it is interesting to note that Mike Smith, founder of WeatherData Services Inc, actually blogged about the hail from this storm as it was occurring, explaining the very strange occurrence of a “hail spike” on radar as the storm moved into Somerset County.

One last radar image I’d like to share is a not-so-commonly seen view of radar (see Figure 7): 3D radar! This radar image enables meteorologists to get a vertical view of a storm , somewhat like an MRI a doctor might have performed on your leg to “see inside” it. As stated on the image, this storm was a “Classic Supercell” – another example of a term you never hear in conjunction with the location Greensburg, Pennsylvania! You can see both the mesocyclone complex on the back edge of the storm (as labeled) as well as the hail core directly in front of it. To be honest, I never imagined I’d be looking at a radar image like this over top my hometown!

Figure 6: A cutaway view of hail, approximately 1-1.25" in diameter.
Figure 6: A cutaway view of hail, approximately 1-1.25″ in diameter.

Figure 7:  A 3D radar view of the supercell over Greensburg, PA at 4:50 PM (dead image link)

tornado damage in Fort AllenAs noted earlier, this storm did cause significant damage to several dozen homes in central Hempfield Township and also the to the Hempfield Area High School. Many photographs of the damage show roofs partially or completely missing. Some buildings also sustained damage to exterior walls, including the dramatic photo shown at left (courtesy of KDKA-TV). According to WTAE.com, this storm has been ranked by the National Weather Service as an EF2 (or “strong” tornado). The tornado was also observed to be about 300 yards at its widest point. Based on damage I have seen, I predict this storm will be rated, at a minimum, a strong EF1 tornado, but more than likely an EF2 tornado. I will update this story with the official results when they are made available.

Wednesday’s storm was easily the worst storm to strike Westmoreland County since at least June 1998 when a signficant tornado outbreak occured across western PA. Although I was watching from the Joel Myers Weather Center at Penn State, I can still say that I have never seen a storm this severe in Westmoreland County. The damage is simply incredible. For one final look, please check out the videos posted below.

Sources:

Data for this article came from many readily-available sources including WTAE.com, KDKA-TV, and the Tribune Review, as well as the National Weather Service. The radar images (Figures 1, 2 and 7) come courtesy of Texas Storm Chasers, while the storm damage photos (Figures 3-5) come from WTAE.com’s uLocal member-upload site and Facebook page.

For more details on this storm check out the Tribune-Review article, KDKA article and videos, and WTAE article.

Videos:

Update: As of 4:00PM on Thursday, March 24, the National Weather Service in Pittsburgh has confirmed the tornado in Westmoreland County as an EF2, or “strong tornado”. More details on the tornado track may still be forthcoming.

Anatomy of a “Surprise” Thunderstorm

The past few days have been very interesting in terms of weather. A massive storm has moved across the country, bringing anything from blizzard conditions to severe ice accumulation. In Latrobe, one of the results was a strong, but very brief thunderstorm that rumbled through Wednesday morning about 8:40AM. The storm surely looked impressive on radar, especially by February standards!

latrobe-020211 radar
8:45 AM Radar from Intellicast

The storm was recorded in a special METAR observation. Normally, these automated observations occur around 50 past the hour, as the image below shows. However, if particularly “interesting” (as the system recognizes it) weather occurs, it can also make a special observation. Such was the case here. The circled portion of the report describes the active weather at the time. It reports light rain associated with a thunderstorm, and ice pellets. Some of the other details, not shown on that chart, include “observed” occasional cloud-to-ground lightning. There’s quite a bit of information you can get from this single automated report!*

metars

One other thing apparently with even that chunk of weather observations in Latrobe is that the cold front passed through at that moment. This can be deduced in several ways. First, we see that the temperature peaks at a whopping 50 degrees at 8:41AM (surprising in February for sure). The temperature begins a pretty [rapid] decent after that point. There was also a wind shift, as winds changed slightly from the WNW to the WSW after that observation. Finally, the pressure reached a minimum at the time of that observation and began to rise again afterwards. A pressure minimum is a surefire sign of frontal passage.

This frontal passage is confirmed on a Weather Underground** surface map from 8:32AM. An occluded front passed through the region at that moment, and the combined effects of warmer, moist, and unstable air led to a very interesting (and unusual) February thunderstorm.

020211-us surface

* – If you want the full METAR (coded), here it is:

KLBE 021341Z 29011G16KT 10SM -TSRAPL SCT038 BKN047 OVC075 10/10 A2956 RMK CB MOV ENE OCNL LTGCG

** – Speaking of the Weather Underground, they just launched an overhauled version of their website yesterday. As always, there has been considerable debate about the design, but I tend to like it. Go check it out for yourself!

Are We Gonna See a White Christmas?

Merry Christmas to all, first off! Hope everyone enjoys a great day spent with family and friends while remembering the real reason for the season (I sincerely hope no one vandalizes that page, it is a concern on Wikipedia I guess)! One important question on everyone’s mind today is “Will there be a White Christmas this year?” Let’s start at the basics to answer this question.

Definition of a White Christmas

I heard earlier this week that some local news stations had conflicting definitions over what a “White Christmas” was. Some claimed that to “get” a White Christmas, an inch of snow needed to fall. This is not true, nor do I believe it will be the case in the Pittsburgh region tomorrow (on Christmas day). According to the NCDC, or National Climatic Data Center (a part of the National Weather Service), a White Christmas is defined as a location having one inch or more of snow on the ground at that particular location. I’ll trust the NWS on this one.

What’s the likelihood then?

In Pittsburgh, we have a 33% likelihood of seeing a White Christmas, based on the NCDC’s climactic data records. Other cities around the state have somewhat higher probabilities, with Bradford clocking in with a 70% chance (Erie was next in line, with a 57% chance). The first image below shows the probability of a White Christmas (in percent likelihood) across the United States. An interesting fact did appear on Wikipedia, stating:

According to research by CDIAC meteorologist Dale Kaiser, the United States during the second half of the 20th century experienced declining frequencies of White Christmases, especially in the northeastern region.

Meanwhile, the NCDC paper (links to both sources at the bottom of this post) says that most of New England (and points westward along those parallels) have a 60% or better chance, generally.

As for Christmas 2010, it’s safe to say we’ll have a White Christmas in Pittsburgh. Almost all areas have a solid inch of snow on the ground, despite a bit of melt off on Christmas Eve due to temperatures getting close to the freezing point. Some areas have seen snow blown around, but overall it should be enough. The second figure below shows the current (as of 12AM 12/25/10)modeled snow depth across the state. During Christmas Day, there will be some flurries to light snow showers across the western part of the state, much as we’ve seen over the past few days. However, I don’t believe it will be enough to make it to a full inch for places that don’t already see it.

One final reminder to close out this article, almost all of the state saw a White Christmas last year, while most of the PA population centers (the southern half of the state, more generally) was snow free on Christmas Day 2008.

Images

Probability of a White Christmas (Courtesy Wikipedia)

Sources

Musicans and Today’s Internet

Who doesn’t love the band OK Go? Even if you aren’t the biggest fan of their music, their always-unique music videos are always worth watching. I think more people know the song “Here It Goes Again” (the third link) as “the treadmill song” than by its actual name. But you know what, these guys get how today’s music works, and the lead singer isn’t all that bad of a writer either! Earlier this year, he (Damian Kulash) wrote a very well-written story detailing why a “net-neutrality” proposal made by Google and Verizon matters, as told by someone who produces andconsumes music. You can read through it here. Just a small excerpt I think is worthwhile in understanding his perspective of the Internet (especially if you don’t feel like reading the whole story):

The Internet is the purest marketplace for ideas that the world has ever seen, and the amazing power of such a level playing field has revolutionized everything. Google knows this better than anyone. It started in a garage and became an industry leader by having great ideas, not mountains of cash. And it’s wonderful: The Internet works! It rewards innovators such as Google, and it relegates protectionist, defensive, idea-squashing fogies such as record companies to the dustbin of history.

Now that the Internet has been around long enough to have developed its own giants, though, we need to make sure they don’t ruin what’s great about the technology that made them. We need to make sure they don’t crush the idea industry the way the music giants crushed the music industry. I hope Google keeps succeeding (seriously, I’m a stockholder), but it must be because of the power of its ideas, not its power to tilt the playing field.

Damian’s next installment, titled “The New Rock-Star Paradigm” is equally well-written (guess it’s good that he’s the lead singer of the band) and interesting. The article discusses his band’s (and other “new artist’s”) measures of success, which are very far from mainstream. It’s also worth the read (if you need a break, you could always watch the videos over again – you know you want to). Nonetheless, I was really inspired to write this post because of how I was alerted to this story. I was linked to it by another one of my favorite bands (even more-so than OK Go), Paper Tongues, who posted it on their Facebook page. Though I suppose an agent or something can update it, I usually (and certainly in this case) have reason to believe that a member of the group itself posted it. I know it even more in this status from yet another band’s (MUTEMATH’s) Facebook page: “Found out the sex of my baby today! I’ll try not to “becoming a dad” barf all over yall, but I’m pretty stoked.-P”

That’s pretty close interaction with the band, if you ask me, and all I had to do was click “Like”. No money was paid or anything like that (I’ve never actually seen any of the bands mentioned in this post in person, but I would love to see any or all of them!). Just another interesting way the Internet, with its massive spread of information, is pulling us all, interconnected, closer together

Lake Effect Snow Longevity

Someone recently asked me “Can you explain to me how it is that we can get snow for 10 days straight, yet we never seem to get rain for 10 days straight?” Simply put, I can blame it on Lake Effect snow. In a nutshell, lake effect snow occurs whenever cooler, dry air passes over the warm lake, such as the Great Lakes. Last week, there was a thriving cold air setup with a strong northwesterly flow (winds coming in from the northwest caused by a low pressure system that had parked itself in eastern Canada and western New England for much of the week. That low pressure system was also responsible for the rather strong winds that were prevalent last week.

Basically, as that cold air moved over the lake, it picked up moisture off the lake, and carried it onto land in Pennsylvania and New York, where it deposited this built-up mositure as snow, and lots of it. Much of northwestern Pennsylvania saw several feet (in upwards of 40 inches) of snow, and these bands did extend far enough south to give much of southwestern Pennsylvania and the western Alleghenies decent accumulation as well (though nothing on that scale).

Because this low had stalled for several days, we were able to milk a lot of moisture out of the lake (think of it somewhat like a sponge) and get snowfall for several days. Lake-effect rain (especially earlier in autumn) is possible if conditions close to the ground are too warm to keep the precipitation snow, but the primary reason we don’t see prolonged periods of steady rainfall (on average) is that the cold air aloft required to produce “lake effect rain” is not in place, and the lake may not be as warm (Lake Erie’s temperature tends to peak in September) and normal rain-producing systems simply do not stay in one place long enough (again, this is a rule with exceptions). That’s not to say we can’t get a ton of rain in a short period of time in other times of the year, but not from the same mechanisms.

For more on lake-effect snow (and it’s associated counterparts), make the visit to Wikipedia (seriously, where else would you look?).