Pattern change near Thanksgiving holiday could bring a cooler start to the month of December

As we near the end of November and get ready to flip the calendar page over into December, we may also flip our pattern into a colder one - at least at the start of the new month. Temperatures through the rest of the week and into the upcoming weekend will remain above average in the 50s with mostly dry conditions expected. But towards the middle of next week, right around Thanksgiving, we may begin to see our pattern change. So, what does this mean? 

Low pressure developing off the southwest coast of the U.S. late this week/weekend will remain cut-off from the main flow of the jet stream, the northern branch riding across the northern tier of the country. As this low moves onshore through the weekend and early next week it'll slowly begin to phase, or merge, with the northern branch. This looks to occur at some point mid-week. Where exactly this phasing takes place and how strong, or weak, it may be are all still questions that need to be answered. But this will likely bring some precipitation to parts of the Midwest, Great Lakes, and Ohio Valley sometime during the Tuesday/Wednesday time frame.

Following the passage of the low there will be a push of cold air from the north, some of which could arrive Thanksgiving Day. But it all depends on just how much those two jet stream branches come together. The more phasing that occurs, the stronger the storm system and southern pull of cold air. While it's a little hard at this point to really pinpoint temperatures and precipitation chances, we can start to recognize the pattern change, and this is highlighted in some of the longer-range outlooks which show the cooler air mass beginning to settle in at the end of the month.