Friday, July 11, 2014

Major Cool Down Next Week Similar to July 2009

Get ready for a major cool down next week!

This picture of Cedar Point in winter might be overdoing it a bit. If you are heading there next Wednesday, I would suggest bring a sweatshirt.

While I was skeptical on biting to quick on this solution late last week, I quickly made adjustments Monday to reflect the huge changes for next week for two reasons:

1) The recurving typhoon. Typhoon Neoguri began a trek northwest then recurved toward Japan. When Typhoons recurve like this, it is a reflection of the overall hemispheric pattern which if followed "downstream" over North America typically means a major cool down across the eastern half of the US. This idea is called "The Typhoon Rule". 

A ridge of high pressure in the western Pacific deflects the typhoon. This boosts the trough over the Gulf of Alaska which keeps the western US ridge going which in turn drives the trough/cool across the eastern US.  While this "rule" shouldn't be used to determine specific day-to-day forecast details for any location, it gives us a very good indication of the overall jet stream pattern. Based on that, we can get a general idea of what to expect 6-10 days in the future.

2) Model performance: I didn't bite on the cool down was simply the models kept showing the trough/cool pocket over the east flattening which was suggesting a warming trend back into the mid 80s. A quick look at the model performance showed that they were having a tough time beyond 5 days probably due to the erratic behavior of the developing El Nino and the atmosphere's response to it. (Note the up and down SOI numbers--South Oscillation Index).

However, the models started to trend "not-so-warm"again (I like that wording versus "cool" since 70-75 degrees isn't really cool) where they have stayed all week.

The probability of temperatures above 90 degrees might not make it north of Dallas or central Florida according to the CIPS site.
Remember July of 2009? A major cool down occurred that month between 7/17 and 7/20 which mirrors what is coming next week.

Aside from Monday, get ready for a week that is about 8-10 degrees below average. Very comfortable but probably not pool weather.