Good morning Weather2020 bloggers,
We have made it to Thanksgiving week and on this Sunday morning, just four days away from the big holiday, we have a very complex weather pattern developing. The models will continue to have a hard time with what happens between now and next weekend. There is a good chance of some brief blocking developing near the west coast with the formation of a high over low block. How this develops will help determine what kind of weather you experience on Thanksgiving Day and the holiday weekend. There will likely be some impacts on travel, one of the biggest weekends for getting to and from your relatives and friends locations. Let’s take a look.
This first map shows the flow aloft over North America, which is valid Monday night. You can click on the map for a larger view. The flow aloft is unblocked with a broad trough over New England and a digging trough off the Pacific Northwest coast. This energy is going to dive south and form into a rather strong upper low. As this happens, it will provide great conditions for snow at many ski resorts out west. This is something that we have not been able to say in years, especially for California. This is still not a storm coming in with a lot of moisture as it is coming in from the northwest and not the west or southwest, which may happen later this winter.
This second map shows the 500 mb flow (18,000 feet up) valid Wednesday night at 6 PM. The flow aloft is still unblocked. Look closely at the eastern Pacific Ocean. A big ridge is developing and if this closes off into an upper high, then we will finally get the flow to block up a bit. As the flow does begin blocking, what happens next is way too complex for the models to handle and figure out. The upper low is going to be ejected out into the plains and in this process it is likely going to fall apart.
This third map shows the evolution of the high over low block near the west coast. The big upper low is forecast to get kicked out and absorbed into the flow. And, a new upper low is forecast to begin developing over California. This upper low and evolution will also be influenced by the system way off the west coast as it gets caught in the southern branch heading towards California as well. This is really a complex development.
There is a well defined northern branch and the developing southern branch.
This fourth map, above, shows the developing high over low blocking well. The models, by this point have many different solutions. The way this pattern develops in the next week is rather obviously complex. There is a lot to monitor here. There is also a tropical system sneaking into the equations south of Cabo san Lucas.
Now what does all of this mean to you? For Thanksgiving Day a strong cold front will have developed and it will only be inching its way eastward. That will be a very cold air mass with some Arctic Air Mass characteristics. Temperatures will likely be below zero near the center of that air mass up north.
Look at where the front is lining up at 6 PM Thanksgiving Night:
Now, imagine you are me, or you are one of the 100,000 people thinking of going to see and experience the tradition of the Plaza Lighting that takes place every Thanksgiving Night at just before 7 PM? This is a forecast map valid at 6 PM Thursday. If this solution is exactly right, then the forecast would be for a 100% chance of rain around that 6-7 PM time frame. And, that front is strong. If it is six hours slower, then it will likely by in the lower 60s for the Plaza Lighting. If it’s six hours faster, then it would be in the 30s. Maybe now you can see why Kansas City was the #1 most unpredictable city in America for big cities in the United States. We have a big challenge ahead.
What would slow it down? That upper low needs to sit back over the southeast and hold together just 12 more hours. Let’s see how today’s models handle this interesting development.
Have a great Sunday. Thank you for reading and participating in this LRC Forecast Experience Blog. Have you entered the forecast contest yet? We are forecasting for the the week of Christmas.