Pattern Amplification Likely, A Tale Of Two Octobers

Good afternoon, 

I want to give a quick update on what the weather pattern looks like as we head into the 2nd half of October. There are some interesting features that deserve some attention. 

The mega-typhoon that is re-curving near Japan is going to spark pattern amplification downstream into North America. The global upper air wind pattern is going to change so that colder air makes its way into the U.S. while warmer air overtakes Canada. I'll show you what I mean... 

Here is a look at our current 500mb pattern from the 12z GFS model. Fairly zonal in the eastern U.S. with a cut-off trough in the western U.S. At this point, a ridge is just now beginning to develop in the Northern Pacific and the EPO (eastern pacific oscillation) is transitioning to a negative phase. 

When we fast forward to the weekend, a full fledged ridge is now dominating in the Northern Pacific and a 

-NAO/-EPO pattern ensues. The -EPO basically means the upper level winds in the Northern Pacific have transitioned from a progressive stage to one that is cut-off by a large ridge, allowing colder air bottled up in Canada to downstream into the U.S. 

And even going beyond the weekend into next week, the GFS still has a PV (Polar Vortex) over the Hudson Bay with a nice trough in the eastern U.S. At this point though, the -NAO is gone but the -EPO signal is still there. 

Just in case you were wondering, the EURO model also has the same set-up as the GFS in regards to the upper level pattern. Strong ridging in the N. Pac. and potent lower heights in the eastern U.S. 

You can see negative temp. anomalies are going to overtake nearly two-thirds of the country by the weekend and into next week. This definitely calls for cooler than normal temperatures to filter into the central and eastern U.S., possibly as high as -8 to -12 degrees below normal, which is fairly significant. Of course if you are a cool-weather enthusiast, this is all music to your ears. 

In terms of precipitation, the amplified pattern is going to bring wetter conditions into the heart of the country and New England as well. 

The PNA, or western ridge, has been non-existent since fall has begun. There has been constant lower heights, or trough's, in the western U.S. This is evident by the large blizzard that brought parts of the Rockies states 40+ inches of snowfall. 

One of the downfalls with not having a western ridge is all the energy that comes with the -EPO consolidates in the western U.S. or middle part of the country. What this usually leads to is storms that cut to the west of the NYC Metro area. If the PNA were in a positive phase, this means the entire west coast of the U.S. is under positive height anomalies and the energy is forced to consolidate somewhere along the east-central or eastern U.S, because that is the way the jet stream would flow. 

Here is a general map I made with my thoughts on this months second half. With the pattern coming to life, there will be more storms to keep an eye on that should bring mainly rainy conditions to the Northeast. However, the upper tier of the country and interior PA/NY could see their first flakes of the season depending on how much cold air is available from the -EPO/-NAO pattern. If the -NAO subsides, much of these storms will likely cut to our west. 

We'll see what happens! Have a good day. 

Francesco Paparatto

Notes:

1. 2013-2014 Winter Outlook to be released Thanksgiving Day

2. Join the forum! www.njstrongweatherforum.com

3. Happy Columbus Day!