UNIVERSITY PARK – The final chapters of the weather story for 2012, of course, have yet to be written, but halfway through the year the plot will surely focus on the dramatic swing in precipitation trends, according to a hydrologist in Penn State’s College of Agricultural Sciences.
After the extremely warm and dry winter Pennsylvania experienced — one of the mildest since records began being kept — very dry conditions prevailed, and there was no snow in the mountains to melt and replenish streams and groundwater. That led to drought worries, noted Bryan Swistock, extension water resources specialist.
“Most people were probably not aware of it, but by the end of April, there were definitely real concerns about a drought,” he said.”To be that dry, at that time of year when it is usually wet — it looked like a bad situation. We were set up for a pretty severe drought if things had not changed.”
But change they did, in a major way.
It started raining frequently in May, and it has not stopped. In fact, in the eastern half of Pennsylvania, it was one of the top 20 wettest Mays on record, Swistock pointed out. Except for northwestern counties, which remain slightly below average levels of precipitation, most areas of the state are now at or above average for precipitation.
“The change in weather patterns has been dramatic,” he said. “And the long-term weather predictions that I have seen indicate the wet weather will continue.”
Some climatologists attribute the abrupt change in weather patterns to the transformation of ocean currents in the South Pacific that affect weather — from a La Niña phenomenon to an El Niño.
“Everything that I’ve been reading from the climatologists suggests that there will be more of the wet weather we have been seeing in Pennsylvania,” Swistock said. “And under this El Niño scenario, they predict we are likely to get more tropical storms. If the remnants from even one hurricane or tropical storm track directly over the state this summer or fall, that could have a huge impact.”
Penn State weather expert Paul Knight, senior lecturer in meteorology, Weather World host and Pennsylvania state climatologist, is dubious about the connection between Pennsylvania’s spring and summer weather and Pacific Ocean currents. But he agrees that the wet weather trend should continue for awhile.
“El Niño effects are much stronger in the wintertime — the summer season is really a muted message at best,” he said. “I don’t think that there is any clear message that Pennsylvania is more likely to see more tropical cyclones in an El Niño year versus an average year.
“Now will there be more storms in an El Niño? The answer is yes, El Niño years normally produce a few more storms. However, El Niño and La Niña are never potent in May, June and July.”
The dominant story of Pennsylvania’s weather so far in 2012 is that it’s been so mild, Knight explained. The first half of the year has been exceptionally warm — 4 or 5 degrees above normal.
“That March warm spell was really unprecedented,” Knight said. “The other thing is that January, February, March and April all averaged well below normal precipitation. And just about the time we were getting uncomfortably dry — and we were well on our way toward a drought — the rains came just in the nick of time.
Jeff Mulhollem, Penn State University