March 8, 2011
The weather of recent days has brought the Midstate the best of March: wacky and wild conditions that signal the transition from winter to spring. Sunday's storm certainly had the best (or worst) of both seasons. Heavy rainfall enveloped the region for most of the daylight hours, while some spots north of Harrisburg got blanketed with wet snow during the night. March often brings this type of weather because there is a battle going on right above our heads. Warm air and cold air are duking it out in the atmosphere for supreme cy. Ultimately, the warmer air will win out as we head toward spring, but for now, the cold air is still hanging tough. Just like in life, change can be difficult. The change in the atmosphere at this time of year is filled with tumult as the death and darkness of winter gives way to the light and life that signal the start of a new season of hope...spring!
This map shows the surface features as they appeared Sunday afternoon. The low pressure area was still sitting well to our south at this point. Notice, though, there are actually two lows sitting over Virginia and North Carolina. The secondary low caused the snowfall to rapidly intensify over northern areas late Sunday night. As this low worked its way up the Appalachians, it pulled a ton of moisture with it and all the dynamics were just right to create a "bombogenesis" effect...in other words...something that doesn't happen often. This event was nearly impossible to forecast. We knew the rain could end as some snow...after all...we only got a little over an inch in Harrisburg. However, the sheer amount of snow for some of our northern towns was shocking.
There was another ingredient that contributed to the "bombogenesis". Notice the high pressure in southern Canada. Due to the flow around the high, cold, arctic air was allowed to drain down the spine of the Appalachians and settle in over the parts of the Midstate. Consider this: we had a temperature near 60 degrees early Sunday morning and by Sunday evening, the temperature had fallen by as much as 30-35 degrees! The cold air came in quickly and there was still plenty of moisture to work with in order for a big snow event to occur across northern zones. The surface map tells all, and this one paints a nice picture of why Sunday's event took place.
This radar image is from overnight Sunday. The area circled indicated the heaviest snow and where the storm just opened up and exploded over central and north-central PA. The cold air moved in behind the front extremely rapidly and just attacked. This battle was indeed won by the colder air aloft, but as I mentioned above, we know the ultimate outcome...eventually the warm-air will be the victor. It's just a matter of time...we hope! The areas hardest hit by this storm (at least in terms of snowfall) are shown below in graphical form:
The pink bullseye shows where the snow piled up quickly Sunday night. The rest of the area didn't see much at all. Either you got it...or you didn't. That's what was so surprising about this storm. Take a real good look at where the pink area is shaded...what do you notice? The heaviest snow fell right along the main stem of the Susquehanna River. This is not good news because of what is waiting for us starting tomorrow and continuing into Thursday. More heavy rain is on the way and with all that snow waiting to melt right into the river (and with the rivers already running very high), serious flooding issues could be a concern right through the upcoming weekend.
Here are the latest projections through Thursday evening. Once again, I think it's possible for the area to receive between 1.5 and 2.5 inches of rainfall. Combine all the water with the snow melt that will take place...you have big problems. The National Weather Service has already put several counties under a flood watch from Thursday morning through Friday morning. Please visit abc27.com/weather and click on your county to read the latest watch. We will of course have updates all week long and stay on top of this ongoing situation. In the meantime, enjoy this nice, pleasant Fat Tuesday!