September 2012 Weather Outlook

Yes, I acknowledge it’s September 19th and this is rather late.  It’s been a busy few weeks.

Let’s get right to it.  Here’s the CPC outlook for temperatures in the US during September:

Similar to August, the CPC projects a chance of above normal temperatures for much of the country.  The only exception (in the lower 48) is along the west coast – although it’s shifted south from the northwest to California.  Unlike August, the CPC isn’t quite as bullish in their above normal temperature outlook (no 50% or 60% shading this month).  This is probably a good thing considering the GFS ensemble forecast for temperature anomalies over the next 10 days (through the morning of Septemer 29 – so, almost the end of the month):

Global Ensemble Forecasting System (GEFS) 10 day temperature anomalies valid through 8AM EDT September 29.

Now, this is only 10 days of a 30-day month, but the substantial cooler-than-normal temperatures forecast here would go a long way toward proving part of the September outlook inaccurate.  The western tail (and even the extreme eastern end) may still be correct if this forecast comes to pass, but a large chunk in the middle of the country could be wiped out.

Accurately forecasting precipitation anomalies is much more difficult, but that doesn’t stop the CPC from doing it.  Here’s their projection for the month of September:

This just seem so specific for a time of year when thunderstorms (and other convective systems) are still common.  I can tell you that, so far, this outlook is fairly accurate.  The only exception is along the Gulf Coast where precipitation has been slightly below normal in much (but not all) of the shaded region.  We’ll see how the rest of the month plays out.  It only takes one or two significant storms (like the one earlier this week) to dramatically affect the monthly total.

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