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...

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...

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,...

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! 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!* 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...

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! 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...