Assuming the forecast verifies pretty well, which is highly likely this close based on GEFS PNA forecasts having done quite well, the upcoming +PNA peak would be highly anomalous though not really all that extraordinary because ASO strongly + peaks occur much more often for some reason than during other months as you'll see below. And that's nothing new. I'd love to know the reason!
The GEFS is suggesting a high chance at a peak of 2.8+ in early Aug. Since 1950, there have been only 6 peaks of 2.8+:
- 3.397 09/24/08
- 3.328 07/02/82
- 3.160 08/01/09
- 3.142 09/28/79
- 3.112 09/30/59
- 2.965 09/26/02
So, the last one was 12 years ago. Note that all 6 occurred during JAS meaning the upcoming early Aug peak fits in fairly well with this climo. Interestingly though, 4 of the 6 were within the tiny interval of the last week of Sep!
Since 1950, there have been this many peaks by month of 2+ adding to a total of 59 peaks or ~once per year:
Jan 0
Feb 2
Mar 0
Apr 2
May 2
Jun 7
Jul 7
Aug 12
Sep 16
Oct 10
Nov 1
Dec 0
So, since 1950, there were only 7 peaks of 2+ during Nov-May or once every 10 years with the highest being only 2.353! Only 2 of the 72 DJFs had one and they were both in very late Feb: 2/29/68 and 2/28/83. OTOH, a whopping 38 of the 59 (~2/3) occurred during ASO with all 10 in Oct during Oct 1-12!
Source for daily PNA: ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.pna.index.b500101.current.ascii
7/29/21 GEFS PNA forecast:
Edit: It may be a coincidence, but note that the strong +PNA frequency peaks with the peak of SSTs.
The GEFS is suggesting a high chance at a peak of 2.8+ in early Aug. Since 1950, there have been only 6 peaks of 2.8+:
- 3.397 09/24/08
- 3.328 07/02/82
- 3.160 08/01/09
- 3.142 09/28/79
- 3.112 09/30/59
- 2.965 09/26/02
So, the last one was 12 years ago. Note that all 6 occurred during JAS meaning the upcoming early Aug peak fits in fairly well with this climo. Interestingly though, 4 of the 6 were within the tiny interval of the last week of Sep!
Since 1950, there have been this many peaks by month of 2+ adding to a total of 59 peaks or ~once per year:
Jan 0
Feb 2
Mar 0
Apr 2
May 2
Jun 7
Jul 7
Aug 12
Sep 16
Oct 10
Nov 1
Dec 0
So, since 1950, there were only 7 peaks of 2+ during Nov-May or once every 10 years with the highest being only 2.353! Only 2 of the 72 DJFs had one and they were both in very late Feb: 2/29/68 and 2/28/83. OTOH, a whopping 38 of the 59 (~2/3) occurred during ASO with all 10 in Oct during Oct 1-12!
Source for daily PNA: ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.pna.index.b500101.current.ascii
7/29/21 GEFS PNA forecast:
Edit: It may be a coincidence, but note that the strong +PNA frequency peaks with the peak of SSTs.
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