Typical fall pattern continues; possible “October Surprise”

Our very standard fall pattern–of warm afternoons and cool mornings, with occasional dry wind events and dampened heat waves interespersed–continues this week. Temperatures will be coolest today and will increase going into the weekend, potentially rising above normal levels (near 90 in warmer inland areas). All in all, there is very little of interest over the next 7 days or so.

Just after day 7,  however, there may be something to talk about. The current pattern of rather boring skies and climatological temps is being supported by a rex blocking pattern in the Eastern Pacific. The associated low pressure area will become a bit stronger and shift south to just SW of the CA coast by day 8. There is some small potential, if the low actually does set up in this position, for the circulation to advect some subtropical moisture into the state from the south. The real story begins, on day 10, though, when the GFS begins to break down the blocking pattern and undercuts the prevailing ridge by a powerful Pacific jet. The last three GFS runs have all indicated strong storm systems making landfall in CA by day 12/13. Since it is still very early in the season to have storms of that magnitude, I would expect that the GFS is overestimating the ability of the jet to overcome the stability of the lingering summer pattern. There is one caveat, though: the Madden-Julian Oscillation, which has been rather dormant in the past couple of years (as it often is during La Nina years) may be becoming more active. This could lead to earlier-than-usual storminess. Depending on the evolution of the MJO over the next week or so, there may be a change warranted in the Seasonal Outlook. We shall see. Stay tuned…

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