More signs of a change... (1-5-11)
We’ve seen some more data that points to a change in our pattern come the middle of the month. One key index we look to is the AO (Arctic Oscillation). It tracks air pressure up in the arctic and when it is positive (like it has been for the past 2 months) pressures are low in the arctic and jet stream winds are more ‘zonal’ (west to east) Cold arctic air has a hard time dropping into the eastern United States and sticking in this pattern. When it goes negative the cold air has an easier time of dropping into this part of the country. A lot of last winter’s cold and snow can be attributed to a negative AO index.Fast forward to today and I saw this chart which plots out the AO index into the future based on what the GFS ensembles are saying:
Courtesy: Climate Prediction CenterThere have been some signs for the last week that the AO would go negative toward the middle of January but I was a bit skeptical of the 14 day forecasts that come out every day. Since the middle of November the track record of the 14 day forecast has been less than stellar. Notice on the graph above that the blue line (the forecast) hasn’t matched up well with the black line (reality). Over the last couple of days, however, the forecast has come into better agreement with what’s actually going on so perhaps the GFS has a better handle on the change coming our way. The change is now even showing up in the Climate Prediction Center’s 8-14 day forecast;
Courtesy: Climate Prediction CenterThis may be the first time this winter season I’ve seen a below normal temperature forecast for us in the long range. Until we get to this point (late next week/next weekend) our temperatures are still going to average above normal. I just sent our latest 7 day forecast to our web page and there are 40+ high temperature on 5 of the next 7 days! It’s after that that the AO goes negative and the changes to colder weather start. More details to follow as we get closer to the change..
Copyright 2012 Newport Television LLC All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
