Monday, 23 September 2013

Cold First Week of October Likely, Despite warm euro weeklies

The weather world has been buzzing lately about a very warm start to the month of october. Most people have been banking on the latest run of  the european weekly model, forecasting balmy conditions in the great lakes/northeast part of the u.s. I don't believe this will be the case, and will explain my reasoning in this post. 

A major -AAM pulse is currently underway which is helping boost equatorial easterlies and an alaskan ridge.
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We are seeing the EPO index respond to this in the short range with a major dive into -1 to -2 territory. This promotes warmer then normal temps across alaska/western canada with arctic air intrusions downstream, especially if this coincides with a -AO event.
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The GWO may be key to determining the weather pattern for the first week of october. Based on lowering AAM in first week of the month, a mean trough over the east looks more favourable despite a warm look to the euro weeklies. Heres the GFS forecast with a major drop in AAM by week 2. If this can coincide with a -AO/NAO, look out! Again, this type of evolution would help transport heat from the tropics towards the gulf of alaska therefore driving the -EPO and downstream pattern.
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GFS ensembles are picking up on this  pattern in 1st week of october with several members showing a pretty robust ridge in the west with troughiness downstream. So the message I am trying to send across is that we may see the potential for an indian summer in the west with another major cold shot for the great lakes and east. between october 1st and 8th. Get your winter gear out and get ready for the fall temperature roller coaster!
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