Record PNA of 4.00 on 8/6/21 obliterates old record

[GaWx]

 The GEFS runs of the last few days have been predicting an unusually strong +PNA coming up in early August. Here's today's GEFS PNA forecast, which if anything is a bit stronger overall:

 

 Based on this forecast, the PNA is going to skyrocket the next 2 days and approach, if not reach, 2 tomorrow (8/1) and approach, if not reach, 3 on 8/2. Afterward, the mean suggests it will quite possibly drop slightly on 8/3 before probably rising again some. It is projected to be 2+ anywhere from 6 to 8 days within 8/1-8 with 8/2-7 very likely being 2+. Also, it is projected to be 2.5+ anywhere from 4 to 6 days within 8/2-7 with 8/3-6 having a good chance to be 2.5+. There quite possibly will be several days over 3 within 8/2-6.

 The largest # of days on record at 3+ back to 1950 for any one peak is only two, which occurred 9/23/08 and 9/24/08. The two days of 3+ could be matched and maybe even exceeded. The highest PNA on record is 3.397 from 9/24/2008. It will probably get pretty close to that with some chance to even exceed it. There have been only four other peaks on record with a 3+: 8/1/2009, 7/2/1982, 9/28/1979, and 9/30/1959. So, interestingly enough, three of the five peaks at 3+ were within Sept 24-30 and all 6 were during JAS. Thus, the upcoming peak in early Aug is sort of in line with very strong peak climo.

 

Now check out the peak dates for the 11 recorded peaks of 2.5+:

 7/2, 7/14, 8/1, 9/24, 9/24, 9/26, 9/28, 9/30, 9/30, 10/4, and 10/6

 Note how they're so concentrated within 9/24-10/6 with 8 of the 11 within that 13 day period! I'd love to know the reason.

 

 The largest # of days in a row on record of 2.5+ is six (9/22-27/2008). That run of six at 2.5+ has a chance to be matched.

 The largest # of days in a row on record of 2.0+ is eight (6/27-7/4/1982 and 9/27-10/4/1979). These runs of eight days at 2.0+ have some chance to be matched though that would very likely require it to reach 2 tomorrow. After these, the next longest are 7 days (9/22-28/2008 and 10/5-11/1953).

 

 Here are the number of recorded periods with peaks of 2+ by month:

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 occurred during ASO with all 10 in Oct during Oct 1-12!

 

 Source for daily PNA back to 1950:   ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.pna.index.b500101.current.ascii

[GaWx]

 Today’s PNA started the very sharp rise as has been forecasted by the GEFS for days although it didn’t quite reach 2 with it at 1.67 vs yesterday’s 0.51.

 Today’s GEFS PNA forecast peak (see below) is even higher than the last 3 days. It implies a higher chance to exceed the daily record high of 3.397 (records back to 1950), which was set on 9/24/2008! Moreover, it suggests an even better chance to exceed the current record of two days at 3+ during one peak, which was set 9/23-24/2008.

 Today’s GEFS suggests a good chance for it to exceed 3 tomorrow. It still has a slight fall for 8/3 and then near steady on 8/4 although both may barely remain at 3+ (will be close). Then, it still has a second rise, which is even more prominent than the prior forecasts. It has it easily above 3 on 8/5-6 with a new record high peak above 3.397 quite possibly being set on one or both days! It is suggesting over 3.5 on both days! Then it falls some on 8/7 although it may still be at 3+ for the last time. Afterward there is a sharp fall 8/8+.

 So, today’s forecast suggests not just a good shot at a new record high peak but also a very good shot at a new record high # of days at 3+ with as many as six days during 8/2-7, which would absolutely obliterate the current record (back to 1950) of Sep of 2008’s two days at 3+!

 

[GaWx]

Aug 2nd update:

 Today's PNA didn't quite make it to 3 as it was 2.88. Even so, it's the highest in 12 years and the fun is just starting. Today's GEFS forecast, if anything, is for a slightly higher peak than the prior run had meaning it is still calling for a new all-time record high. It is forecasting 3+ for 8/3-6 with a close call for 8/7. So it is calling for 4-5 days of 3+. The current record for any one peak is only 2 days of 3+ (records back to 1950) , which was in Sep of 2008. So, this would shatter that record!

 

[GaWx]

 Today's update has the first 3+ PNA day since 8/1/2009 with a 3.21 This is only the 7th on record. Still looking for an all-time record high during the next two days. The current record (back to 1950) is 3.397.

[GaWx]

Today, the PNA is at an amazing 3.73, which obliterates the old record high going back to 1950 of 3.397, set on 9/24/2008! The GEFS suggests there will be one more very high day tomorrow:

[StormchaserChuck!]

Good post, something to track, but nothing is showing up in the 500mb.

[GaWx]

3 hours ago, StormchaserChuck! said:

Good post, something to track, but nothing is showing up in the 500mb.

 Thanks, Chuck. We got an even higher PNA of 4.00 today (smack dab at the top of the chart), which absolutely obliterates the previous all-time old record peak for any date back to 1950 of 3.40!! This also makes it three days of 3+ for this event, which breaks the previous record of two days in 2008, and we may even get one more tomorrow:

 

 

Yeah, I have noticed that despite this record high PNA today, the 500 mb pattern today doesn't look nearly as impressive to the eye as prior days. To be sure, the W NA ridge/E NA trof was quite impressive for summer/most impressive to me on August 2, when the PNA was "only" at 2.88:

 However, today's H5 on the day of the PNA peak is already much flatter:

 

 It is almost as if there's a lag in the daily PNA calculation. So, nothing is showing up of note now at h5 but it was showing up impressively a few days ago.

[StormchaserChuck!]

It ended up being pretty decent.. in the Summer the Aleutian Low is a little further north. 

[GaWx]

 Today, we got one last 3+ with a 3.40. That makes four 3+ days  in a row. This is amazing because during the prior 71 years, there was only one time that there were as many as two days in a row! So, this event is by far the greatest +PNA in the 71 years of recorded history. Could this have been a once in several hundred+ year event? Quite possibly.

[raindancewx]

PNA over 1.5 in August from 1950-2020: 1958, 1960, 1977, 1990, 1999, 2004, 2007, 2020 if the month remains very positive. Some other close to +1.5 years include 2011 and 2014.

PNA+ in August correlations:

Sept: How NE US & SW US. Strong correlation to warmth SE Canada & NY state.

Oct: Warm signal West. Strong warm signal for CA/AZ/NV. (similar to -WPO in Feb-Apr, although not in Oct)

Nov: Warm signal nationally - but weak. (Note last year is on the list above and was very warm in November 2020).

Dec: Cold signal for NM/CO/TX, Central Plains, Midwest, NJ/PA - all weak

Jan: Warm signal SW US/New England - all weak

Feb: Warm signal NW US / cold Northern Plains - all weak

Mar: Cold signal Midwest - all weak

Apr: Warm signal TX/NM, cold CA - all weak.

May: Cold signal North & West, hot signal SE - strongest in Texas.

 

Precip:

Sept - erratic at best

Oct - weak dry signal Rockies & Texas & Ozarks

Nov - weak dry signal most of the US

Dec - wet signal SW & Midwest / TN Valley (strong for Northern NM mountains)

Jan - erratic

Feb - wet signal SW & Plains. Looks like the +WPO signal really.

Mar - wet SE US. dry Northern Plains (strong) and Rockies

Apr - wet coasts, dry NM/AZ/TX

May - wet NW/SE, dry SW

[Typhoon Tip]

I'm suspicious of these CPC derivatives ...

It's complex, but I suspect the HC expansion phenomenon is giving them a boost, while this planetary wave # oscillates through.

The inundation of higher non-hydrostatic heights are over-lapping/invading the lower domain/latitudes of the PNA domain, out over the areal expanse of the central/E Pacific is evident. Farther east, there is a balancing geostrophic forcing to nadir the flow E of ~  100 or so W over mid latitudes of N/A; numerically that is a demonstrative +PNA.

Things get interesting considering constructive numerical interference.  You have probaby a legit modest PNA, but with an expanded HC phenomenon in place the two may be artificially inflating the numbers. 

Looking at the operational runs/versions recently, it may also help to explain a sub-540 dm massive, albeit transient, SPV anachronistically passing over the Canadian shield, while 594 dm heights astride the Mid Atlantic.  That's unusual in August, atoning for the +PNA, but the whole construct is also displaced N ... thing a submarine diving below the depth-charges, the trough is deep in y-coordinate, while gliding over at higher latitudes.

Consequently, we are feeding/slipping +20C 850 mb air masses under the southern edge of that trough belly clear to New England late this week.  You don't typically see 21C at 850 in a well mixed lower troposphere over Albany during a historically +PNA derivatives.   

[StormchaserChuck!]

Preceded, or coincided with the +IO, MJO 7-8 SST warming.