It looks like a cut off low will form and move northward bringing heavy rain to the mid sections of our country, while the Northeast gets more showery type rain that has the potential to be heavy at times. Overall, it will not be a big deal. We may see some mixing precipitation off to the west and around the higher elevations, but generally it will not do much. The same cannot be said for areas to the south and west of us. Up to 4 inches of rain is possible where the rain is heaviest and most persistent.
Further south however, this system may bring some unseasonal snow and wet accumulations, especially toward the state Tennessee and surrounding areas. I wouldn't be surprised if some of the TN mountains picked up some decent snow. As we move toward Michigan though, the potential is there for more significant snow, as cold air quickly rushes in and meets up with heavier precipitation. Right now I see the potential for 6+ inches of snow around the Lansing area and places to the north and west of Detroit. Detroit itself may see some decent snowfall as the cold air wraps into the system. It's possible, not very likely, that areas as far west as Chicago see some snow before all is done.
After the system passes, temperatures won't change too much. Cooler than the temperatures that we're currently experiencing, but still above average. It's after the system completely passes and a weak clipper system passes through that we see a strong low form up toward Canada, driving in cold air. The weak clipper system will bring snow showers to some areas, but it certainly won't be widespread. This will help get the initial cold air into the Midwest and Northeast, but won't keep it in those areas. It's the low up in Canada that will break the "warm/cold" pattern. The low will be strong enough to keep the cold air constantly being driven into the United States, like shown in the graphic below.
This cold is unrelated to the NAO, PNA, AO, and the rest of the teleconnections. So those of you who are unsupportive of this cold due to the teleconnections, need to take the time to look at the set up with the cold air next week, and the week after. In fact, the strong low pressure system up in Canada will move slow enough to keep the cold air in place possibly all the way through the end of the first week of December. The potential is there for a possible system to work it's way across the country and into the northeastern United States while this cold air is in place. And you all know what that spells... Yes... The ingredients are there for a snowstorm around the 6th or 7th of December, before the cold air may no longer be available to us. All we need is those ingredients to come together. So while I don't see a major widespread snowstorm taking place around this time period, I do see how a decent snowstorm takes shape. This of course will be something to watch over the next week.
Here's a look at the GFS's depiction of the potential storm around the 6th and 7th:
And here's a look at the Euro's depiction of the potential storm around the 6th and 7th
Both similar ideas of a storm basically being suppressed down to the south while the cold air continues to invade the north. It wouldn't be far fetched to have some of, or a lot of, that moisture move northward into the colder air and make for a nice snowstorm somewhere in between. Just something to think about as we see more and more runs of this storm come in.
Now above I mentioned the possibility of the colder air being cut off sometime after the first week of December. And I do believe in that. We may see a warm up between the 8th or 9th of December and the 12th or 13th of December. It's in between those two time periods that I see the potential for the "pattern changing storm" to take place... yes... the one I have been talking about since the beginning of October. Now I have gotten a lot of questions about my confidence and questions regarding the possibility that this pattern change, and/or storm does not happen. That is ok. It happens. I still remain confident and optimistic about both of those events, but if one, or both, were to not take place... well then it's part of weather and forecasting, and is what I love about this complex field of science! It is often unpredictable! And if it does take place? Great! I was able to pick up on the patterns and clues behind this long range forecasting, and hopefully people will be bright enough to see that. But enough about the ifs and silly questions... Back to the weather...
The "pattern changing storm. Just because I expect it to change the pattern to more of a wintry one, does not mean we are all going to see a major snowstorm. It is likely to contain snow, but not necessarily widespread. Probably more of an interior event if I had to take an early shot at it. The strong system will move through and bring in a rush of cold air behind it. That will get us into a true pattern change in my belief. One that folks who don't follow the weather will even be able to take note of. In fact... It is possible we go through a very cold, and even snowy, period between around December 10th right up until Christmas time.
Here's how the 12z GFS thinks the system works out around the 12th and 13th.
Over the next several days and weeks though, the teleconnections will become a major part of my forecast. They will tell a lot of whether or not my forecast will come together. We NEED the AO to go negative, the NAO to go negative, and the PNA to stay positive. We've seen a lot of wacky things out of the teleconnections over the past several days, so we need to wait for consistency in order for us to say what these wacky teleconnections will do next. That will tell the tail of the winter.
So over the next few days, keep all of this in mind, and don't get too crazy about the upcoming winter yet. We need to wait until around the 10th before we really start getting hyped over for the winter season of 2011-2012. Enjoy the next couple days of weather! They won't last for long!
-Scott P.
