Joestradamus cautions that it is a big IF! Given the recent instability from run to run and models hinting at change but flipping, Joestradamus remains cautious. However the European today and to some extent the other models are indicating that some longer term changes are underway which will shift the pattern to a colder look as we enter the first part of October. However we will want to see several runs of this before locking in.
There have been signals that the Atlantic Oscillation is going “negative” which means ridging will be building in the Atlantic toward and over Greenland which favors troughing in the east and a ridge now in the west which is the signature of colder air coming into the east. It might also be a way we can finally get more opportunities for rain which we desparately need.
We begin to see the change getting underway a week from today. The orange and purple areas signify warmer air aloft or ridging and notice that it is building in the North Atlantic and across Western Canada. If this is correct it means that the colder air transit path form Northern Canada will be established. The question will be over time whether this is going to be temporary or something more permanent.
Troughing in the east becomes exceptionally strong as we move our way through days 8 through 10 as the ridge builds strongly and in particular the ridge in the west is shown to be quite strong with a fairly deep vortex for this time of year pushing southward into the Great Lakes. This should create opportunities for rain as moisture feeds should be able to open up combined with perhaps some better dynamics which have been sorely lacking for many months.
The other important driver is the trough off the west coast which drives southward off the west coast which forces the western ridge to build northward. What allows for more confidence in this run is that there appear to be no make believe tropical systems that are driving changes in the Atlantic. The last few weeks models have been showing non existing hurricanes energizing ridges and troughs in various places causing model runs to be more unreliable than usual. We will wait for confirmation over the next few days but for those of you looking for real Autumn weather, this does look rather promising.
One note on the change in the Atlantic Oscillation. There is a correlation between a strongly negative Atlantic Oscillation and colder winters in the east. The implication is that strong negative Atlantic Oscillation reading in October mean those strong negative signals will be present in the winter. Last October we had a strong negative Atlantic Oscillation in October however it was non existent during the winter! Instead the pattern was dependant and dominated by the action in the Pacific. I put this out there because I am sure this subject will be coming up if this all plays out and we need to be very cautious regarding pattern changes now and what they may or may not mean months from now.
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