Sunday, September 16, 2012

'More Of The Same' Pattern To Continue

One of the best methods of forecasting is to use the persistence method, where you forecast based on past days. For instance, if it were hot for 3 days, you might assume it will be hot again tomorrow. If it were rainy for a few hours and the skies looked dark still, you might think it will keep raining. That rule is being applied to the next couple of weeks.

Currently, there is a big ridge in the West, and a very active storm track in the East. Helping this to happen is a positive PNA and negative EPO pattern. Below are their forecasts for the next 15 days.

Both indices are forecasted by the NCEP (Agency who manages the GFS, NAM, etc.), and the ESRL/PSD (the agency that is more on the technical side of models and forecasting.

Both agencies have the EPO heading negative in association with the ridge forming over the West. Considering it will be a strong ridge, I think the NCEP is correct in its assumption of the PNA over the next 15 days. As you can see, the PNA is much more positive with the NCEP than the ESRL/PSD, and I believe this is the correct way to go, based on how strong the models are with ridging in the West and troughing in the East.

Now that we are heading into Fall, such strong storms should become more common. I do not dispute that this could easily happen again in winter, as there has been much more persistent ridging in the upper latitudes than last year. It will be quite interesting to see if this pattern can get established for the fall and possibly winter.


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