Friday, July 2, 2010

Asian Trough/Ridge Pattern...

I have talked about the Asian trough/ridge pattern before, but I thought it would be cool to quickly relate it to the current pattern.... I hope this will be informative, as I'll try to keep this as short as possible!

Here is last night's 0z JMA 500mb chart valid for 12z June 2nd... Notice a decent trough through Japan, and a strong ridge through SE China... When using this particular teleconnection you have to keep a few things in mind... First Tokyo, Japan correlates to Cape Hatteras, NC... Pretty close to the same latitude! SE China correlates to the Gulf of Mexico... Also, this Asian trough/ridge patterns takes 6-10 days to materialize... Basically, if a trough enters SE China, it should take 6-10 days to get to the Gulf of Mexico... The time of year in theory should give you a handle on whether it's a 6 day teleconnection, or a 10 day teleconnection.. This is where experience is HUGE! The atmosphere doesn't have a calendar, so each year is unique... As the we get into the summer months, and the northern hemisphere warms, the wavelengths shorten... Right now I would say it's around a 7 day correlation...

I know some people may laugh at this type of forecasting, but trust me it works well... Think of it this way... Say I gave you a rope, and told you to stand across the room... If I yanked on that rope, you will feel that yank in a certain time period... The harder I yank the rope, the faster/stronger you will feel it! So the stronger the trough/ridge, the stronger and faster the US should "feel" it... Again, this is where the experience of watching trough/ridge patterns over and over again comes into play... This teleconnection is NOT going to pick up on smaller features like a subtle shortwave or a cut off low... It works best when major amplification is involved! Also, I can't tell you specific details on what will happen 6-10 days later, but I can at least tell you if parts of the US should be under the influence of a trough or a ridge... I try to use this all year round with long range forecasting, but I especially like using this teleconnection with the tropics....

I'm going to relate it to the possible SW Gulf tropical cyclone threat the European is picking up on for next week... Please remember that this teleconnection DOES NOT tell you if development will occur, it only tells you how the trough/ridge pattern should look "if" development does occur... It's another piece to the puzzle that helps me decided if the models have a good handle on the overall pattern... This played a part with my Alex forecast! You had a strong ridge in SE China about a week before landfall, so it was one more reason why I knew the GFS was out to lunch... If it would have shown a trough in SE China, then I may have actually put some stock in the GFS for once... Be careful though, because this teleconnection is just another piece to the puzzle of forecasting, and you shouldn't ever use it on its own... It mainly should be used to help put more confidence in your original forecast!

"If" the European is correct with development in the SW Gulf, then I would say the ridge will hold strong when looking at the current situation in SE China... You have a strong ridge right now, and with possible development in 4-5 days or so (landfall in 7-8 days), I see the ridge holding strong again... I have been watching Asia fairly consistently for the past few days, and the ridge has continued to hold strong in SE China... So if development does occur in the SW Gulf of Mexico this week, don't get fooled so easily into thinking that it will be pulled towards the northern Gulf....

Why do I have this strong feeling the GFS will show a northern bias/movement as it breaks down the ridge too fast again? Hmmm, could it possible be its HORRIBLE handle on heat/heat transfer issues? It almost always has a right bias compared to the actual track! Maybe it won't this time, but if it does, you know where I'll stand again... Ridge holds strong, tropical cyclone moves west! Right now the key is where this possible development starts (The GFS also has a horrible time with bundling heat correctly in tropical cyclone development)... The further south it develops, the further south the impact IMO... Let's see what happens, but at least you now have an idea how the trough/ridge pattern should setup across the Gulf of Mexico!


  1. Excellent write up Greg. The teleconnections have fascinated me since Doug first brought them to my attention in Forecasting class.

  2. Thanks Derek! I'm HUGE into teleconnections, analogs, model biases, and pattern recognition! I'm VERY blessed to have been mentored by someone like Doug! He is one of the very best forecasters in the country!!!

  3. This is fascinating. I only understand about half of what you post, but for a newbie self-taught weather watcher that's not too bad.
    The teleconnection part I get, and it makes perfect common sense.