Philadelphia weather: Frosty Friday start leads to weekend heat

PHILADELPHIA - It's a frosty start to your Friday morning.

Everyone drops into the 30s overnight because the skies clear. Anytime you get to 38 degrees, which is the low for Philadelphia, frost starts forming.

The more the temperature drops, the thicker the frost can get.

With temperatures in the mid-30s in the suburbs, the frost will be a little thicker and more widespread.

Much of the region is under a freeze warning. Portions of Bucks, Chester, Montgomery and Lehigh counties, as well as Burlington, Camden, Cumberland, Gloucester, Mercer and Salem counties are all under that warning.

So, if you live outside of a big city and any of your flowers are sensitive to frost, consider draping sheets or towels over your plants. This will help hold in their heat and hold in the heat the ground gives off.

With perfectly blue, clear skies on Friday, we'll get temperatures up a bit more to the mid-60s.

We're back in the mid-60s on Saturday, and a few spots will see a quick passing sprinkle in the afternoon.

On Sunday evening, a few spots will get see storms. We get storms Sunday because the temperatures are drastically jumping, with highs reaching 80 on Sunday and then 88 on Monday.

All these temperature swings lately are due to the jet stream.

When the jet stream gets very wavy, you get big drops in temperature as cold air spills in from the north, and you get big rises in temperature as warm air flows up from the south.

At the end of next week our jet stream gets less wavy so there won't be these quick jumps in temperature.

Instead, our temperatures gradually slides down next week, eventually bottoming out in the upper 60s.