Medium Range Discussion Summer 2012

[HM]

A thought concerning the prospects for winter blocking...

The June 2012 AO averaged -0.672 and the July AO has averaged +0.09 through July 30. Assuming the AO averages < 0 for the summer (June-August) timeframe, odds would favor the AO's averaging < 0 for the upcoming winter (December-February).

Since 1950, there were 38 cases during which the summer AO averaged < 0. 26/38 (68.4%) saw the winter AO also average < 0.

In cases when the summer AO averaged < 0, a winter AO < 0 was 1.4 times more likely than an AO > 0 during El Niño events. Winter 2009-10 was the most recent El Niño case that saw a negative winter AO.

In contrast, during those 38 cases, a winter AO > 0 was 2.9 times more likely than an AO < 0 during a La Niña. Winter 2011-12 was the most recent La Niña case that saw a positive winter AO.

In sum, if the summer 2012 AO averages < 0 and the upcoming winter experiences an El Niño (or even neutral ENSO conditions), there should be more blocking than last winter. Moreover, a blocky winter would appear more likely than not. Nevertheless, things are not yet cast in stone. Such developments as early-season Siberian snow cover expansion could provide a hint as to how things will turn out during Winter 2012-13.

Don, what are some notable examples of El Nino years that didn't follow the -AO summer to -AO winter correlation? I would imagine 1972-73 is probably one.

[donsutherland1]

Don, what are some notable examples of El Nino years that didn't follow the -AO summer to -AO winter correlation? I would imagine 1972-73 is probably one.

Off the top of my head, 1951-52, 1972-73, and 1982-83 are examples.

[easternsnowman]

Off the top of my head, 1951-52, 1972-73, and 1982-83 are examples.

1972-73 and 1982-83 were some of the strongest ninos and I believe 1951-52 was strong or close to it.

[donsutherland1]

Now that July 2012 is completed, some U.S. record temperature statistics:

- Daily record high temperatures: 4,404

- Monthly record high temperatures: 305

- All-time record high temperatures: 172

- Daily record low temperatures: 313

- Monthly record low temperatures: 14

Ratios:

- Daily record highs : Daily record lows: 14.1 : 1

- Monthly record highs : Monthly record lows: 21.8: 1

Additional Ratios:

- Monthly record highs : Daily record lows: 0.974: 1 (almost the same number of monthly record highs as daily record lows)

- All-time record highs : Daily record lows: 0.550 (for every 1.82 daily record lows, there was one all-time record high)

- All-time record highs : Monthly record lows: 12.3 : 1

It is very likely that July 2012 finished with a mean temperature of 77.0°F or higher for the contiguous United States. The only previous months on record with such warmth are:

July 1936: 77.43°F

July 2006: 77.26°F

July 2011: 77.01°F

July 1934: 77.00°F

[donsutherland1]

August 16-23, 2012 Thoughts:

A less extreme period looks to be on tap. In addition, some appreciable rainfall could occur in some areas.

The charts shown below are as follows:

Left: Composite temperature anomalies for ENSO Region 3.4 anomalies of +0.40°C to +1.00°C, a PNA of -1.00 to -0.25, and an AO of 0.00 to +1.00 for North America.

Top Right: NAEFS forecast for the August 14-20, 2012 timeframe

The Southeast and the Northern Plains have prospects for above normal rainfall. The West Coast looks to have the best chance of being drier than normal.

Taking into consideration all of the date, my thoughts are as follows:

- Near normal in the Plains States, possibly starting cool and then warming up

- Most of Canada should be warmer than normal (southern Alberta, Manitoba, and Saskatchewan could be near normal with some small areas of below normal readings)

- Warmer than normal elsewhere in the United States and the warmest part of the period could be the latter portion in the Eastern half of the United States.

[carley5]

thanks don. looks like a good forecast.

[icebreaker5221]

Looks like we could be seeing quite a cold shot next week. Extremely anomalous summertime polar vortex which has kept the arctic cool this past week will finally break down. As the AO flips from highly positive to negative, this buildup of cold air will be unleashed across North America (as well as eastern Russia). GFS similar although not quite as extreme.

[CoastalWx]

Even the EC ensembles have a -2.5SD -NAO. That probably argues for some sort of a cool shot moving into the north central US and maybe northeast towards d8-10. Euro op might be too aggressive, but it may have the idea.

[Damage In Tolland]

August 16-23, 2012 Thoughts:

A less extreme period looks to be on tap. In addition, some appreciable rainfall could occur in some areas.

The charts shown below are as follows:

Left: Composite temperature anomalies for ENSO Region 3.4 anomalies of +0.40°C to +1.00°C, a PNA of -1.00 to -0.25, and an AO of 0.00 to +1.00 for North America.

Top Right: NAEFS forecast for the August 14-20, 2012 timeframe

The Southeast and the Northern Plains have prospects for above normal rainfall. The West Coast looks to have the best chance of being drier than normal.

Taking into consideration all of the date, my thoughts are as follows:

- Near normal in the Plains States, possibly starting cool and then warming up

- Most of Canada should be warmer than normal (southern Alberta, Manitoba, and Saskatchewan could be near normal with some small areas of below normal readings)

- Warmer than normal elsewhere in the United States and the warmest part of the period could be the latter portion in the Eastern half of the United States.

No relief in sight for the next 10. Euro way too bullish on any cooldown

[MJO812]

No relief in sight for the next 10. Euro way too bullish on any cooldown

Euro ensembles agree with the op but not to an extent of the op. That makes the cool down that the Euro is advertising a little more plausible.

[easternsnowman]

The bottom line is the heat for the most part will be gone.

[icebreaker5221]

No relief in sight for the next 10. Euro way too bullish on any cooldown

Maybe not so much in your backyard, but much of the northern Great Plains are definitely in for a cool-down relative to what they're had the last couple of weeks.

[Ozarkwx]

Wondering what to make of the recent cooldown and a 8-14 day forecast for below average temps in the central US. Does it appear that the "death ridge" that has baked the Plains finally been dislodged from its anchor? Or is this more of a reverse January thaw?

[donsutherland1]

Wondering what to make of the recent cooldown and a 8-14 day forecast for below average temps in the central US. Does it appear that the "death ridge" that has baked the Plains finally been dislodged from its anchor? Or is this more of a reverse January thaw?

With the ENSO Region 3.4 anomaly having risen to +0.8°C, I suspect that one is probably beginning to see the emergent El Niño exert an influence on the overall pattern. I'm not yet sure whether this recent cooldown will prove to be a temporary or more enduring pattern as we head into the fall.

[Ottawa Blizzard]

With the ENSO Region 3.4 anomaly having risen to +0.8°C, I suspect that one is probably beginning to see the emergent El Niño exert an influence on the overall pattern. I'm not yet sure whether this recent cooldown will prove to be a temporary or more enduring pattern as we head into the fall.

Don, El Nino Falls tend to be chilly, correct? I recall that October/November 1997 and 2002 were quite chilly.

[Ottawa Blizzard]

Maybe not so much in your backyard, but much of the northern Great Plains are definitely in for a cool-down relative to what they're had the last couple of weeks.

And yet Winnipeg Manitoba has temperatures of 80F forecast later this week, which is above average for them. Yet another case of above average anomolies the further north you go?

[okie333]

Wondering what to make of the recent cooldown and a 8-14 day forecast for below average temps in the central US. Does it appear that the "death ridge" that has baked the Plains finally been dislodged from its anchor? Or is this more of a reverse January thaw?

IMO it's a bit of both... don't bet the farm on it but I think there will be a very warm/dry period near Labor Day, lasting 1-2 weeks. After that the major pattern change, indicative of a weak Niño but expanded northward, occurs.

[SoCoWx]

IMO it's a bit of both... don't bet the farm on it but I think there will be a very warm/dry period near Labor Day, lasting 1-2 weeks. After that the major pattern change, indicative of a weak Niño but expanded northward, occurs.

So are you expecting the south and east to continue to bake? Or will this cover the entire eastern half of the nation?

[donsutherland1]

August 24-31, 2012 Thoughts:

Another week of possibly seasonal to even somewhat cool readings on average appears likely for the central United States.The charts shown below are as follows:

Left: Composite temperature anomalies for ENSO Region 3.4 anomalies of +0.50°C to +1.30°C, a PNA of +0.50 to +1.50, and an AO of -0.50 to +0.50 for North America.

Top Right: GFS Ensembles (August 25-29, 2012)

As one can see, there are disagreements between the teleconnection analogs and GFS ensembles. Additional differences can be found in the NAEFS and CFSv2 weekly forecasts. Such disagreements likely suggest that a large-scale pattern change may be evolving. It is likely that the recent warming of ENSO Region 3.4 to anomalies of +0.80°C is beginning to have an impact. In other words, the emergent El Niño has arrived and is beginning to influence the pattern.

In terms of the ongoing drought, even as the core of the drought area is likely to see generally below normal rainfall, areas on the periphery of the drought could benefit. As a result, the overall area covered by the drought will likely shrink somewhat. The Southeast, Northern Plains, and Great Lakes regions have perhaps the highest probability of seeing above normal rainfall.

The evolution of the MJO indicates a timeframe possibly favorable for the development of tropical cyclones, though the rising El Niño will have a damping effect, from late August until perhaps mid-September. Afterward, the Tropics might shut down with very little activity afterward. Given the MJO forecast, it is plausible that some of the potential for enhanced rainfall in the Southeastern U.S. showing up among some of the teleconnection analogs could imply a tropical connection.

Finally, taking into consideration all of the date, my thoughts in terms of temperatures are as follows:

- Near normal in the Plains States with areas of cool anomalies

- Most of Canada should be somewhat warmer than normal (southern Alberta, Manitoba, and Saskatchewan could be near normal with some small areas of below normal readings)

- Warmer on both the West and East Coasts. If the PNA forecast is accurate, the potential for a bout of much above normal readings could exist for the Pacific Northwest.

[Ozarkwx]

Thanks Don and Okie. Trying to figure some logistics that are weather dependent, and not helped by excessive heat. It seems that "trying to get a jump" on the project by betting on an early end to summer weather might be taking on a risk where there is no clear percentage in our favor. Anyway, it will be interesting to see what the new long range forecasts say that come out on Thursday.

[donsutherland1]

Thanks Don and Okie. Trying to figure some logistics that are weather dependent, and not helped by excessive heat. It seems that "trying to get a jump" on the project by betting on an early end to summer weather might be taking on a risk where there is no clear percentage in our favor. Anyway, it will be interesting to see what the new long range forecasts say that come out on Thursday.

FWIW, toward or just after August 31, the Plains States could again warm up based on some of the teleconnection analogs. That's too far out to have much confidence, but it would be similar to what one saw back in the spring. Given the rising El Niño, there's greater uncertainty, as we'll have to see whether ENSO begins to impact the pattern. Even the August 24-31 period has much greater uncertainty than usual.

[Riptide]

Based on your analysis, It appears that the long-range pattern into Late August and Early September would favor long-tracking tropical cyclones; and a greater chance of landfall. NAO is also expected to become positive again as we approach September. If the upper-level setup is anything like last Spring; then I expect less recurve potential compared to earlier this month.

[donsutherland1]

A few evening thoughts...

In recent days a portion of Greenland, especially interior Greenland, has turned colder to much colder than normal. In addition, cooler air has moved into the Plains States. At the same time, the ENSO Region 3.4 anomalies have continued to warm, reaching +0.8°C for the week centered around August 8. The ensemble guidance is forecasting a period during which the PNA will rise above +1.

All of this is similar to developments that were unfolding in 2002, which has been a very good summer analog to date. In fact, the week centered around August 7, 2002 had an ENSO Region3.4 anomaly of +0.9°C. Late August 2002 also saw the PNA rise above +1 for a time.

Overall, 2002 is one of the stronger analogs currently showing up for September. There are others in the mix, including 2009 which has again shown up, but pattern persistence may tilt the balance toward 2002. In addition, recent runs of the CFSv2 have shown September anomalies fairly similar to those of 2002.

At this point, it is still too soon for me to make a call for September. However, it is interesting that 2002 has been a long-running analog and is in high in the mix for the start of fall.

[SVT450R]

Impressive cool shot in the Midwest for August 445 low temp records from the 13th to the 20th.

[donsutherland1]

September 1-7, 2012 Thoughts:

September appears likely to start very warm in portions of Western North America but closer to normal elsewhere.

Left: Composite temperature anomalies for ENSO Region 3.4 anomalies of +0.40°C to +1.20°C, a PNA of +0.50 to +1.50, and an AO of 0.00 to +1.00 for North America.

Right: GFS Ensembles (September 2-6, 2012)

The first week of September represents another week that shows no more of the coast-to-coast warmth that had predominated during much of the summer. It also offers a fresh indication that the emerging El Niño is beginning to impact the pattern.

In terms of the ongoing drought, the areas where the drought is worst are likely to remain relatively dry. There was a strong signal on the teleconnection analogs for wetter weather in the Great Lakes region and also along the Gulf Coast. It is possible that the wetness showing up in the Gulf Coast could relate to Isaac, which could make landfall somewhere along the central Gulf Coast to Florida Panhandle depending on which model one looks at. After that the storm could move fairly slowly and that's probably what's showing up on the teleconnection analogs.

In terms of the tropics, some of the dates showing up in the analogs e.g., 9/8-9/1969 saw Gerda track toward Maine. The first week of September could still be reasonably favorable for tropical cyclone development based on the MJO. Should such a system develop it could pose a threat to areas farther east than Isaac will, though there is no assurance that the storm track would be onshore. The only thing that might reasonably be gleaned is a farther east track for any such tropical cyclones.

Taking into consideration all of the data, my thoughts in terms of temperatures are as follows:

- Near to somewhat warmer than normal in the Plains States; warmest readings in the Central Plains

- Warmer than normal across Western Canada and the western third of the U.S.; the Pacific Northwest could see a period of much warmer than normal readings.

- Cooler than normal in the Southeast and perhaps Gulf States

- The remainder of the U.S. and Canada could be near to somewhat above normal.

Finally, with Arctic sea ice measures likely to approach or set new record lows, questions arise as to what this might mean for the winter. Some literature suggests that such an outcome, especially if Siberian snowcover increases during the fall, could result in a blocky winter. Other literature suggests that the outcome would be a slower eastward progression of systems, meaning that AO regimes (positive or negative) could be lengthier than would otherwise be the case. At this point in time, analogs and statistical correlations based on the summer blockiness suggest that a more blocky outcome than Winter 2011-12 continues to be more likely than not. However, as blocking is difficult to predict for more than two weeks in advance, such an outcome is not cast in stone at this point in time.

[Isotherm]

Nice post Don. I'm in agreement with most of it. I also came up w/ analogs for my Sept outlook that strongly suggest a wetter than normal pattern for the gulf coast/SE states with the dryness continuing for the Plains. My only real difference would be placing the cool anomaly over the Upper MW, with near normal in the Gulf Coast, above normal in the Northeast. Actually I think the August temp departure map to date (Aug 1-21) will look pretty similar to the Sept final map (but not as significantly cool in the MW).

[donsutherland1]

Nice post Don. I'm in agreement with most of it. I also came up w/ analogs for my Sept outlook that strongly suggest a wetter than normal pattern for the gulf coast/SE states with the dryness continuing for the Plains. My only real difference would be placing the cool anomaly over the Upper MW, with near normal in the Gulf Coast, above normal in the Northeast. Actually I think the August temp departure map to date (Aug 1-21) will look pretty similar to the Sept final map (but not as significantly cool in the MW).

Isotherm,

My thoughts only concern September 1-7, not the whole month. I'll post those later this week.

[Isotherm]

Isotherm,

My thoughts only concern September 1-7, not the whole month. I'll post those later this week.

Oh ok - missed that part. Look forward to reading your thoughts.

[Midlo Snow Maker]

Impressive cool shot in the Midwest for August 445 low temp records from the 13th to the 20th.

very impressive after the July we had

[trapperman]

Bump.