All of Central Pennsylvania will feel and see a change in our weather pattern this weekend. This week started out a lot like summer with warm/hot afternoons and high humidity but end of the week will feel like fall/winter. So what flipped the switch from summer to fall?
The Jet Stream:Is a narrow bands of strong winds in the upper levels of the atmosphere. The winds blow from west to east in jet stream but the flow often shifts to the north and south. The jet stream is the boundary between hot and cold air.
Summertime Pattern: This past summer was hot and humid and that weather pattern continued well into fall. The jet stream during the summer months retreats north well into Canada do to the angle of the sun being more direct over the northern hemisphere and heating up the ground. During the fall months the sun retreats south moving towards the equator allowing the jet stream to move south ushering in colder air.
What kept us so warm and humid through October was a high pressure system off the coast of the eastern seaboard. This high pressure system brought hot and humid air north keeping the jet stream and the cooler air in Canada. The high pressure system that kept us in that summertime pattern is no longer there do to a strong cold front and the remnants of Michael pushing it away.
Fall Pattern: With the high pressure moving east and a strong cold front marching east across the United States the weather pattern will finally become cooler. The jet stream will sink south and set up over Pennsylvania. This will allow the boundary of cold air to finally move into the United States. The jet stream will remain over Pennsylvania for the next several days and that will keep us in the fall time pattern.