Weather Update: December 1, 2010

Ah, the changing of the months; the changing of the seasons. It’s official – December is here! (And in case you were wondering, I say the “changing of the seasons” because meteorological winter begins on December 1.) For some reason, this time of year always seems to bring interesting weather. Let’s take a look at some of those interesting events.

An Anniversary: 4 Years Since the Last Tornado in Westmoreland County

It’s been four years already since the last time a tornado struck Westmoreland County. Don’t get me wrong, there has been plenty of severe weather since then, but December 1, 2006 was the last time a tornado was officially reported. This twister, an F1 (and likely one of the last tornadoes recorded before switching to the Enhanced Fujita, or EF, scale on 2/1/2007) touched down briefly just west of Westmoreland Hospital in Greensburg (Fort Allen area) around noontime. It damaged about a dozen homes before skipping up the central reaches of the county, knocking over many trees.

My most famous recollection of the storm also involves downed trees, but was not caused by the tornado. On the other side of Greensburg (Hempfield Township, actually), a large part of a forest was flattened by straight-line winds which struck in a northwesterly fashion. How do I know it was straight-line winds and not tornadic activity? Every last one of the 60 or so trees that fell is facing the exact same direction. Interestingly, if you go past this forest (easily viewable from PA Route 130) today, you’ll see the damage just the same.

The Tribune-Review still has some articles on their website from the tornado. Take a look here or here(dead link).

Rains Soaks the State

I’m sure you’ve realized how much it rained over the past day or so. According to weather observations taken atop the Walker Building at Penn State, 2.58 inches of rain fell between 7AM yesterday (11/30/2010) and 7AM today. There was also a slight amount of rain before 7AM yesterday, and the rain continued right on past 7AM today as well, before changing over to snow (more on that in a minute). This rain hasn’t really been coming down fast enough to cause flash flooding, but there certainly has been enough rain for some flooding, especially along the seemingly hydrophilic Mon Wharf in Pittsburgh (More details here).

It seems we really like seeing heavy rainfall on the 30th day of months with only 30 days. Say what? Think back to September 30, when we received over 3.5 inches of rain! For whatever reason, very heavy rainstorms seem to occur on those days. The good news is that the next month with only 30 days is not until April 2011. So perhaps we have a while to go before seeing a rainstorm like this again. (If only, if only…)

Snow Strikes State Next

Today, we’re in a time of rapid change, as a strong cold front passed through the state earlier this morning. Interestingly, it was another strong cold front that caused the tornado discussed above. This time, we saw temperatures again nosedive, but just without the severe weather associated. Again, according to data recorded at the Walker Building weather station, the high temperature of the day was 59.9 degrees, recorded at 3:47AM. From there, temperatures fell, and fell quickly so that by 10:00AM temperatures were down to about 34 degrees and the rain had changed over to snow.

How drastic of a temperature change was this? Figure this: between 6:50AM (when the temp was 51.8) and 7:10AM (when the temp was 45.1), a span of only 20 minutes, the temperature dropped 6.7 degrees! That works out to a drop of a third of a degree per minute! For the bigger picture graphically, check out the chart at right.

And while we’re not expected to see a huge amount of snow, especially snow that sticks to the ground, it certainly won’t be bad for a second meaningful snowfall of the season (though the northwest corner of the state should see some decent accumulation). So what are you waiting for? Get out there and catch some snowflakes on your tongue!