Four of the last nine days featured highs in the 80s, but we may be saying goodbye to the summer-like warmth for at least the next week. Much like this past winter (and much of this spring), the north Atlantic is entering a state dominated by high pressure over Greenland. This pattern known as a negative North Atlantic Oscillation (-NAO) typically brings cooler air south into eastern North America. In addition, a ridge of high pressure has been located over western North America and Alaska, further helping to pinch the colder air south into the northeast US. This change begins tonight as an earlier cold front will bring in our first round of chill.
This pattern will be in no hurry to change. Below average temperatures are expected through at least the middle of next week. The average high in Harrisburg is now in the low 70s, and we’ll remain 5 to 10 degrees below that through next Wednesday. Given that our flow will be largely out of the west and northwest, a mainly dry pattern is expected, but periodic showers will occur this weekend in the transition especially Mother’s Day afternoon. A few showers can be expected Friday and Saturday as the cold pocket of air moves overhead, but most of those days will be dry.
High pressure will build over Pennsylvania early next week, bringing the return of sunshine but keeping us seasonably cool with highs in the mid-60s. Overnight lows through next week will be in the 40s, not cold enough for any frost or freeze concerns at this time. We should pull out of this cooler pattern toward the end of next week as the -NAO state relaxes and our flow comes more out of the south. In the meantime, don’t lose put away those jackets just yet!
-Meteorologist Adis Juklo