July 10, 2014
With the renewed chatter of the “Polar Vortex” summer style 2014, I thought that it might be a good idea to look back at last summer, and the flow pattern that was in place at the beginning of July 2013.
The 120 hour forecast, one of the images that I had archived, during the beginning of last Summer’s monsoon, is shown below. This pattern, with the monster ridge of high pressure over the Mountain West and a complementary trough in the middle of the nation, is not that dissimilar to the set-up due this coming week, 13-17 July 2014. What is really different is the DEPTH of the trough of low pressure. As the center value, lowest number, is in the 573 range, where this year, 2014, the value is in the mid 550s. Substantially lower, in fact about 2.5 Stand deviations below normal.
For comparison sake, the last image is from early January 2014 showing the very same jet stream pattern, but with far far colder values. The lowest value, over Lower Michigan in in the lower 490s.
What does that value mean? 490 mean 4900 meters at the 500Mb level, the half-way up, pressure wise through the atmosphere. The colder it is the more dense and compressed the gasses of the atmosphere become. During the the summer months the typical value should be in mid 580s, equating to high temperatures in the 80s and lower 90s.
Our summer weather in North America peaked in heat during the summers of 2011 and 2012, last year was markedly cooler and this summer will be cooler yet.