Another Winter Puzzle Piece

ScreenHunter_01 Nov. 29 14.39

A lot to go over on another beautiful afternoon around the KC area as clouds are starting to increase in the region ahead of a weak disturbance that will fly through the area later this evening with some showers and rain. Amounts are expected to be anywhere from nearly nothing for some to upwards of 1/4″ for others. Timing is between 9PM and 3AM or so. So the window is pretty short.

Aside from that the weather looks great through most of Thursday. There is going to be some sort of front or wind shift heading this way on Thursday and I’m becoming a little concerned that there may be some showers in the region sometime later Thursday or Thursday night. Something to watch for the week. Weak push of cool air on Friday, slightly stronger push on Saturday then we really warm back up again later next weekend into the last week of November.

With that said, there will be a lot of cold air building across NW and Western Canada as this all happens and I’m beginning to grow more confident that at least some of that air should get to us sometime between the 27th and 29th or so.

Before I get into the Winter Forecast stuff that I was going to talk about…I wanted to share some neat video with you from Down Under. Australia is actually now going into their severe weather season and they too get tornadoes and waterspouts. actually compared to the USA, their tornados are far fewer, about 20 across the country, and Australia is pretty darn big. Yesterday however, one of the more photogenic waterspouts I’ve seen was captured in Batemans Bay which is south of Sidney. Check out this amazing video!

OK now let’s move on. Ive blogged quite a bit about the thoughts I put into the Winter Forecast. To remind you it airs on Tuesday night @ 9PM on FOX 4. With that said I want to give you another piece of the puzzle. I’ve given you about 5-6 so far and here is another one. It’s called the Arctic Oscillation (AO) and relates to the surface pressure patterns up towards the Arctic region. When the pressure is low up there the AO is positive (+AO). When the pressure is high up there that means the AO is negative (-AO).

During +AO times the jetstream is blowing strongly and rather steadily from west to east. This keeps most of the cold air botttled up across the far northern territories of the Northern Hemisphere. When there is a -AO, the flow is lighter and subject to more “buckling.” This allows the potential for the colder air up there to be delivered into the middle latitudes…and yes into the USA. I saw this image on Wikipedia and it shows what I’m talking about nicely.

 

The AO and the NAO (North Atlantic Oscillation), which I blogged about quite a bit the other day do indeed work together sometimes, and when both indices turn negative, especially sharply negative it’s usually a good indicator of the better chance of cold air delivery into the USA. When we were so cold and snowy a couple of winter’s ago, these indices were sharply negative and it really was something to see from that standpoint, and it was very indicative of the amount of blocking in the atmosphere that existed.

So how is the AO doing these days? Take a look by clicking on the image below to make it larger.

What you are looking at is the analysis of the AO on the top of the chart, and then the forecasted values off the GFS model for the future. From the analysis part we can see that the AO since early summer has varied quite a bit from + to -. That is not unusual. The times in the + territory though are not long (about 7-10 days or so. Interestingly to me, when the AO wants to go negative…it does in a big way for a sustained period of time. Something else I’ve noticed in the chart. Look towards the bottom of the chart. That is the forecast for the AO values over the 14 days. Notice how the model wants to try to create more of a -AO value, whereas the reality is that the index is much more variable. That tells me that the GFS is especially vulnerable to generating cold air masses that don’t verify as well as what really happens. Something to think about when these models create these brutally cold airmasses that catch peoples attention 10-14 days out, but never really materialize. It is sort of complicated I realize, and really just because one index does something interesting, I really look for the companion NAO index to respond or lead the way in doing something similar. When the two indices are united than I’m more interested in what their values are.

It should be noted that this is not something set in stone. I’ve seen plenty of winter -NAO/-AO scenarios that don’t really do a lot and likewise with +NAO/+AO values. One thing though is when the values, whether +/- are on the extreme side, that is a good signal something really cold is possible (negative) or really warm (positive).

By the way, forecasting this way is using a tool called “teleconnections.” Again not a hard and fast definite way of attaining better winter forecast accuracy, but just another tool to try and get a “feel” of the winter ahead.

Oh and one last thing, last night I created a graphic showing the snowfall over the past 30+ years, going back to 1980. It really is amazing to see the variation over the last 3 winter seasons. From all that snow in 2009/10 and 2010/11 to nothing in 2011/12.

We’re recording our Winter Forecast Roundtable tomorrow afternoon as part of our Winter Forecast for Tuesday night. I’ll give you a hint, the odds are heavily favored that I will be going below average for the winter to come in terms of snowfall. I seem to have a number between 15-19″ in mind. There I gave you, our loyal bloggers another hint!

Joe

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