Temperatures have been on a roller coaster for what seems like months. The most recent ride? A high of 77 degrees at the Philadelphia International Airport Saturday, followed by a high of only 45 degrees Sunday, and forecast temperatures in the low 70s by tomorrow. In addition, it’s been a rainy stretch of days. Let’s break down exactly what’s going on with our weather pattern.
Weekend Rise and Fall
This past Saturday we saw temperatures climb all the way to the upper 70s, with just isolated showers across the area.
Why? A large storm was set up to the west of our region. North of us was a boundary layer (this one a cold front) that was connected to this storm. That layer was dividing the cold air from the warm air trying to surge in from the southwest. Our area was under the warm air “zone”. Meaning, the cold air was kept north, and with southwest winds, our atmosphere was being fed warmth to boost our temperatures well above average (21 degrees above average in Philly, to be exact).
But, all good things must come to an end. And they did, quite quickly. Overnight Saturday into Sunday morning, the winds shifted direction. Take a look at the wind map from one model. It shows the winds coming almost directly from the east (the non-tail end of the barbs points in the direction the winds are going). An east flow forces chilly ocean air atop us. As the winds shifted, this led the way to the cold front slinking southward across our area.
The result? A high of only 45 degrees in Philadelphia (as in 11 degrees below average and 32 degrees colder than the previous day).
As we sat ahead of the storm center, which was creating severe thunderstorm threats to central and southern portions of the country, we also sat in a rather moist set-up. That means we had plenty of moisture in the sky (thick clouds) all the way down to the surface (something we’ll sometimes refer to as high dewpoint temperatures) So, we were able to tap into periods of light rain showers and misting. However, not much steady rain was experienced over the weekend.
Monday Return to Warmth
Remember that warm air that was surging over the region from the southwest on Saturday? Well, it made a comeback quickly on Monday.
Winds shifted direction again Monday morning. Take a look at the wind map below for Monday. It shows the barbs constantly flowing in from the southwest. A warm air pump!
In addition, a warm front stalled over the southern half of the region.
As a result, especially in southern zones across our region, temperatures made a return to the 60s and even 70s. Temperatures were cooler farther north due to the stalling of the warm front. The warmth continues Tuesday. In fact, Tuesday morning temperatures will be quite mild in the 50s, and highs will again be spread from north to south. Southern zones should see 70s, again. Mid 60s are possible for Philadelphia. Lower 60s or upper 50s for northern most spots.
Scattered Thunderstorm Potential
With warm air across the region, some isolated to scattered thunderstorms are possible as yet another system passes just to our south Tuesday afternoon. Isolated showers may cross the Delaware Valley in the morning Tuesday, but with the storm centers’ passage late day, enough energy across the region could bring some spotty thunderstorms to the area. These storms are not expected to be severe. The best chance for thunderstorms will be the warmest locations, south.
Here’s a look at one model projection for the late day thunderstorm potential:
Notice the small spots of orange and red on the map near us. This indicates the scattered nature of the storms.
Overall, we’ll remain cloudy through Tuesday, but finally see sunshine breakout Wednesday. Temperatures Wednesday will also take one last tumble, although not as grand. Temperatures are forecast in the upper 50s and low 60s.
More rain to come by late week! We’ll get into more detail on that in the days to come.