2013 Fall Medium Range Discussion

[donsutherland1]

An additional note on the forecast blocking...

 

If the blocking develops as shown on the ensembles, it would be historic for the second half of March. Since 1950, there have been 1008 days in the March 16-31 period. Just 1 of those days saw the AO fall below -4. Only 4 days saw the AO fall to -3.75 or below.

 

The 5 lowest figures for the March 16-31 timeframe are:

 

1. -4.202, March 24, 2001

2. -3.952, March 25, 2001

3. -3.822, March 21, 2006

4. -3.758, March 21, 1955

5. -3.714, March 22, 1955

[NJwinter23]

Great stuff Don. Very impressive block in the offing here, and might I add that the euro ensembles also look very threatening in that window of time between the 23rd and 27th. 

[pazzo83]

An additional note on the forecast blocking...

 

If the blocking develops as shown on the ensembles, it would be historic for the second half of March. Since 1950, there have been 1008 days in the March 16-31 period. Just 1 of those days saw the AO fall below -4. Only 4 days saw the AO fall to -3.75 or below.

 

The 5 lowest figures for the March 16-31 timeframe are:

 

1. -4.202, March 24, 2001

2. -3.952, March 25, 2001

3. -3.822, March 21, 2006

4. -3.758, March 21, 1955

5. -3.714, March 22, 1955

 

I just thought it would be interesting to look at the temps for the following 20 days in NYC after those top 3 negative AO anomalies:

 

March 24/25 2001

3/26: 37 27

3/27: 41 24

3/28: 48 30

3/29: 45 36

3/30: 43 37

3/31: 46 37

4/1: 43 37

4/2: 48 37

4/3: 55 37

4/4: 54 37

4/5: 64 42

4/6: 54 48

4/7: 54 43

4/8: 45 41

4/9: 78 45

4/10: 62 48

4/11: 53 44

4/12: 57 44

4/13: 73 51

4/14: 66 46

 

March 21, 2006

 

3/22: 44 30

3/23: 53 34

3/24: 52 39

3/25: 47 38

3/26: 51 37

3/27: 57 37

3/28: 55 43

3/29: 63 41

3/30: 66 46

3/31: 68 51

4/1:  73 53

4/2:  66 46

4/3:  57 46

4/4:  55 43

4/5:  46 33

4/6:  53 39

4/7:  66 46

4/8:  63 37

4/9:  57 37

4/10: 62 42

[Kaner587]

It looks like it takes around 10 days from when the maximal point of blocking occurs for temps to rebound to normal/above status. For us that would take us well into the 4th wk of march if not first week of April assuming this is the end of blocking. If it just weakens and reloads as just occurred, well, then we can pretty much kiss the idea of warm temps in the last wk of march or early April goodbye.

[The_Global_Warmer]

Anyone have any take on the ENSO warming and warm sub surface temps?

[donsutherland1]

Anyone have any take on the ENSO warming and warm sub surface temps?

 

Aside from being confident that the persistent neutral-borderline La Niña conditions that predominated during a large part of the winter have now come to an end, I'm still uncertain whether the summer/autumn will feature neutral ENSO conditions or witness the development of an El Niño. Given the uncertainty and statistical models, my guess leans toward neutral ENSO conditions. If one recalls, from the same point last year, the dynamical models were quite bullish on the development of an El Niño for the winter. The statistical models had a cooler outlook and wound up much closer to what happened. More often than not, it seems that the statistical models have been more skillful at timeframes longer than 6 months, hence I'm giving them greater weight.

 

Globally, the lack of a La Niña and predominant neutral ENSO conditions will probably result in a warmer year than last year (perhaps even a top 5 one). In terms of North American weather, it wouldn't surprise me to see April start cold courtesy of the blocking and then see a shift toward notably warmer conditions as the spring progresses and neutral ENSO conditions (biased a little on the warm side) prevail.

[FL510]

Here in Northeast Ohio it looks like March 2013 has a good chance of being 15-20°F colder on average vs. March 2012.  Amazing extremes.

[donsutherland1]

Amazing late-March winter pattern developing…

 

The ingredients in what should put the finishing touches on the snowiest March since 2009 (and even earlier in some places e.g., New England) in an area that includes the Midwest, Ohio Valley, portions of the Middle Atlantic States, New England, southern Ontario and southern Quebec are poised to fall into place.

 

First, the seemingly perpetual blocking that has seen the Arctic Oscillation (AO) negative for 38 consecutive days is likely to undergo a dramatic strengthening. After peaking at -0.737 yesterday, the AO has now fallen to -1.063.  

 

The GFS ensembles continue to indicate that the AO could fall to historic levels for this time of year. Today’s run shows a large number of ensemble members pointing to a figure at or below -4.5 and a number going to or below -5.0.

 

 

The latest date on which the AO fell to -4.5 was March 12 in 1970 when the AO stood at -4.552. The latest date on which the AO fell to -5.0 was March 10 in 1970 when the AO reached -5.115.

 

Bluewave has written a nice piece about the forthcoming blocking. It can be found at: http://www.americanwx.com/bb/index.php/topic/39715-one-of-the-strongest-late-march-500-mb-blocks-in-the-forecast/

 

In terms of the practical impact of such blocking, opportunities for snowfall could exist with any storms that develop. Prior to March 21-22, there could be opportunities for storms to cut. For much of the rest of March, if the blocking develops as forecast, it would be more difficult for storms to cut. More likely scenarios would include possible suppression, coastal storms, or secondary redevelopment near the coast.

 

In terms of the modeling, the 3/15 0z ECMWF and 3/15 0z and 6z runs of the GFS have been exciting runs, particularly for parts of New England.

 

 If any of those runs verify, Worcester could be headed for the most snow on record for the February-March period. To date, Worcester has seen 67.4” snow during February-March 2013. Only 1967, which holds the record at 70.1” has had more snow over the February-March timeframe.  There would even be the prospect that Worcester could approach or exceed its all-time two-month record of 74.8”, which fell during January-February 2005. To date, Worcester’s seasonal snowfall is 101.0”. That’s the 4^th highest seasonal figure on record. The next target, which would be in reach according to the above guidance, is the 1960-61 figure of 104.3”.

 

My opinion of prospects for at least some accumulation of snow for the 3/15-3/25 timeframe for select cities is as follows:

 

Boston: Very Likely

Burlington: Very Likely (at least one accumulation of 4” or 10 cm or more is possible)

Chicago: Likely

Cleveland: Likely

Harrisburg: Likely

Hartford: Very Likely

Kansas City: Possible

Montreal: Very Likely (at least one accumulation of 4” or 10 cm or more is possible)

New York City: Possible

Ottawa: Very Likely

Philadelphia: Possible

Toronto: Likely

Washington, DC: Possible

Worcester: Very likely (at least one accumulation of 4” or 10 cm or more is possible)

[griteater]

 

The Cohen Oct Eurasian snow cover advance -> AO correlation worked well again this winter

[GaWx]

Folks,

 Per the 0Z 3/16 GEFS, the AO is forecasted to dip to near -5 or lower 3/19-23 (yes, 5 days of sub ~-5) with a low ~-5.5 within 3/20-2!! This is even lower than prior runs! How unprecedented is this? Well, going back to 1950, when daily AO records start, there has not been a single day near or lower than -5 between 3/11 and 11/16, inclusive! Actually, there have been sub -5 days in March only in 1970 and that was seven days in early March (3/4-10).

 

 How crazy is this? The 0Z 3/16 and earlier Euro runs have had a 1064 mb sfc high and 566 dm 500 mb hts. centered over the N pole on 3/19!

 

 Considering how anomalous is this AO dip, the major S showing for parts of the SE US on 3/22 on the 0Z 3/16 Euro is not far-fetched at all.

 

 Thanks to Don S. for being all over this for several days.

[AvantHiatus]

In the context of the atmospheric anomalies. The severe -AO would create above normal temperatures in the arctic, perhaps reaching record territory along the west coast of Greenland. Last year at this time the AO was weakly positive and the polar vortex was on the other side of the hemisphere and confined to Siberia and parts of Europe. Creating record warm temperatures during the winter and spring of 2012 in North America.

 

A similar negative AO event occured in 2010 which eventually led to the warmest year on record, ranking close to 1998 and 2005 in terms of global temperatures. However, it's important to note that there was a moderate el nino in 2010, contributing some or most of the warming.

 

[easternsnowman]

In the context of the atmospheric anomalies. The severe -AO would create above normal temperatures in the arctic, perhaps reaching record territory along the west coast of Greenland. Last year at this time the AO was weakly positive and the polar vortex was on the other side of the hemisphere and confined to Siberia and parts of Europe. Creating record warm temperatures during the winter and spring of 2012 in North America.

 

A similar negative AO event occured in 2010 which eventually led to the warmest year on record, ranking close to 1998 and 2005 in terms of global temperatures. However, it's important to note that there was a moderate el nino in 2010, contributing some or most of the warming.

 

Perhaps a record hot summer is coming.

[wxmx]

A great deal of the current -AO peak (valley) is being caused by a Himalaya's mountain torque event originated in late February, which caused a Rossby wave which entered the arctic via the Bering strait, disrupting the already disturbed PV, which weakness can be traced back to January's MMW. The lower strat PV never fully recovered from the MMW event, and is being a factor on the major AO dip that's ocurring right now.

 

[donsutherland1]

Historic Late-Season Blocking Getting Underway...

 

This morning, the Arctic Oscillation, which has now been negative for 41 consecutive days, stood at -3.654. There remains strong consensus that the AO will likely fall below -4.500 and possibly -5.000.

 

 

 

This pattern remains a potent one. There will likely be continuing opportunities for snowfall in eastern North America as the blocking deepens and persists, perhaps for much of the rest of the month. Following the storm likely to impact the East today through Wednesday, there will be an increasing risk that any subsequent storms could be coastal storms, redevelop along the coastline ( Miller B ), or perhaps even be suppressed.

 

With respect to the March 18-20 storm, should New York City pick up 0.1" or more snow, that would be NYC's second accumulating snowfall after March 15. March 16 saw 0.3" fall. The last time there were two accumulations of snow after March 15 occurred in 2000 (March 17: 0.4" and April 9: 1.2").

 

In the meantime, parts of New England will continue to enjoy what has become a special winter and extraordinary two-month stretch. To date, February-March has seen 67.4" fall at Worcester. The February-March record of 70.1", set in 1967, should fall. The two-month record of 74.8", established in January-February 2005 could be approached or exceeded.

 

The storm's heaviest snows should extend across central and Northern New England into southern Quebec. All those areas have a good chance at seeing 10" (25 cm) or more snow.

[Kevin Druff]

Don -- Could I possibly trouble you for some research in regards to succeeding summers? There was some conjecture earlier in the thread about heat following record spring blocking. Is there any credence in the climatological record that we have to support such a thesis?

Historic Late-Season Blocking Getting Underway...

 

This morning, the Arctic Oscillation, which has now been negative for 41 consecutive days, stood at -3.654. There remains strong consensus that the AO will likely fall below -4.500 and possibly -5.000.

 

[donsutherland1]

Don -- Could I possibly trouble you for some research in regards to succeeding summers? There was some conjecture earlier in the thread about heat following record spring blocking. Is there any credence in the climatological record that we have to support such a thesis?

For VA, warm summer anomalies are twice as likely as cool ones. In New England, the Northern Plains, and Great Lakes region, chances of either outcome are fairly close. Although it's early, my analog pool is biased on the warm side right now for the summer.

[Chinook]

Why isn't the CPC NAO index picking up the blocking configuration today?  Surely you would think this index would be -2 to -3, but it only has -0.8.

[griteater]

Why isn't the CPC NAO index picking up the blocking configuration today?  Surely you would think this index would be -2 to -3, but it only has -0.8.

 

Just looking at the anomaly maps, I suspect that the CPC NAO index calculation is station-based, i.e. the difference in pressure anomalies between Portugal and Iceland...whereas if you look at the initialized NAO value from today's 12z GFS from Alan Huffman's site, it shows an NAO value of around -2.0.  I'm pretty sure that he uses the full north Atlantic basin for his calculations, and also has west vs. east based calculations for the NAO.

 

http://raleighwx.americanwx.com/models/12zgfsindices.html

[heavy_wx]

Just looking at the anomaly maps, I suspect that the CPC NAO index calculation is station-based, i.e. the difference in pressure anomalies between Portugal and Iceland...whereas if you look at the initialized NAO value from today's 12z GFS from Alan Huffman's site, it shows an NAO value of around -2.0.  I'm pretty sure that he uses the full north Atlantic basin for his calculations, and also has west vs. east based calculations for the NAO.

 

http://raleighwx.americanwx.com/models/12zgfsindices.htmlshould

 

Actually the CPC NAO calculation is much more involved. It is based on the projection of the daily 500 mb height anomalies onto the leading NAO rotated EOF.

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/history/method.shtml

 

To get a strongly negative NAO, the 500 mb anomaly pattern will need to be simlar to the negative of the REOF.

 

[uncle W]

tomorrow could have the lowest AO reading of the season...many times when the ao was at its lowest point NYC had snow/cold or both...As I look out my window here on March 18th it's snowing with close to an inch on the ground...Not bad for March 18th...the last three years were springlike on this date...

[griteater]

Actually the CPC NAO calculation is much more involved. It is based on the projection of the daily 500 mb height anomalies onto the leading NAO rotated EOF.

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/history/method.shtml

 

To get a strongly negative NAO, the 500 mb anomaly pattern will need to be simlar to the negative of the REOF.

 

 

OK, good to know.  Based on that info, I would think today's 500mb anomalies would support a more negative NAO than -0.7...but maybe the negative height anomalies across the central basin of the north Atlantic aren't strong enough.

 

 

 

[Kevin Druff]

Don -- Could I possibly trouble you for some research in regards to succeeding summers? There was some conjecture earlier in the thread about heat following record spring blocking. Is there any credence in the climatological record that we have to support such a thesis?

For VA, warm summer anomalies are twice as likely as cool ones. In New England, the Northern Plains, and Great Lakes region, chances of either outcome are fairly close. Although it's early, my analog pool is biased on the warm side right now for the summer.

Thanks, Don. Can't say I am super excited about a hot summer after 2 record hot summers in a row. My electricity bill would prefer less heat to fight off.

[donsutherland1]

Building on Message #706, it was previously noted that Worcester is having an exceptional stretch of wintry weather. New York City is also having a nice late-season resurgence of winter weather.

 

With today's snowfall, New York City has now had 2 accumulations of snow after March 15 for the first time since 2000. Some of the guidance suggests that a third accumulation is possible within the next week or so. The last time New York City had 3 accumulations of snow after March 15 occurred in 1965. Since 1950, there have been three such occasions: 1956 (4 accumulations), 1960 (3 accumulations), and 1965 (3 accumulations).

 

The snowfalls after March 15 for those years were as follows:

 

1956:

March 16-17, 1956: 6.7"

March 18-19, 1956: 11.6"

March 24, 1956: 1.2"

April 8, 1956: 4.2"

   Total: 23.7"

 

1960:

March 17, 1960: 1.5"

March 22, 1960: 1.9"

March 26, 1960: 0.2"

   Total: 3.6"

 

1965:

March 17, 1965: 1.1"

March 20, 1965: 1.7"

April 2, 1965: 1.2"

   Total: 4.0"

 

Finally, what's interesting is that both 1960 and 1965 showed up among my top March analogs (#631).

[donsutherland1]

Thanks, Don. Can't say I am super excited about a hot summer after 2 record hot summers in a row. My electricity bill would prefer less heat to fight off.

I share those sentiments. Right now, I don't believe Summer 2013 will be quite as hot as the last one was.

[uncle W]

Building on Message #706, it was previously noted that Worcester is having an exceptional stretch of wintry weather. New York City is also having a nice late-season resurgence of winter weather.

 

With today's snowfall, New York City has now had 2 accumulations of snow after March 15 for the first time since 2000. Some of the guidance suggests that a third accumulation is possible within the next week or so. The last time New York City had 3 accumulations of snow after March 15 occurred in 1965. Since 1950, there have been three such occasions: 1956 (4 accumulations), 1960 (3 accumulations), and 1965 (3 accumulations).

 

The snowfalls after March 15 for those years were as follows:

 

1956:

March 16-17, 1956: 6.7"

March 18-19, 1956: 11.6"

March 24, 1956: 1.2"

April 8, 1956: 4.2"

   Total: 23.7"

 

1960:

March 17, 1960: 1.5"

March 22, 1960: 1.9"

March 26, 1960: 0.2"

   Total: 3.6"

 

1965:

March 17, 1965: 1.1"

March 20, 1965: 1.7"

April 2, 1965: 1.2"

   Total: 4.0"

 

Finally, what's interesting is that both 1960 and 1965 showed up among my top March analogs (#631).

good stuff Don...your other analog 1967 wasn't to shabby also...1967 had 2.6" on the 15-16th...3.0" on the 17th and 9.8" on the 21st-22nd...The AO this morning is almost -5.000...incredible for this time of year...

[Kevin Druff]

I share those sentiments. Right now, I don't believe Summer 2013 will be quite as hot as the last one was.

Don, are you adding the DC "non-storm" from earlier this month to your archive? I have some pictures from my home where we got a surprise 4" in Richmond if you're interested.

[donsutherland1]

Don, are you adding the DC "non-storm" from earlier this month to your archive? I have some pictures from my home where we got a surprise 4" in Richmond if you're interested.

Absolutely. I'd love to add some of the photos from that event.

[donsutherland1]

Today's AO: -4.848. The AO is now lower than it has ever been this late in the season. The latest date on which the AO was at least as low as the current reading was March 10 in 1970 when the AO stood at -5.115.

[donsutherland1]

AO Falls Below -5.000...

 

The Arctic Oscillation stood at -5.632 today. That's, by far, the lowest reading ever after March 15. It's also the lowest reading after March 6 (when the AO was -6.114 in 1970).

[ApacheTrout]

Don,

 

When the Climate Prediction Center issued its forecast for March on February 28, I noted that, in their reasoning, they gave little credence to using the AO (among others) as a predictive tool:

 

4) THE ARCTIC OSCILLATION (AO), THE SIMILAR NORTH ATLANTIC OSCILLATION (NAO), AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE ANOMALY PATTERN ESPECIALLY DURING BOREAL WINTER AND ARE GENERALLY CONSIDERED TO HAVE LOW PREDICTABILITY.

 

But you've plainly shown over the past two weeks and again over the past few winters that substantially negative AO values are useful as a leading predictor for temperatures in the eastern U.S.  Any thoughts on why they'd dismiss something that seems to useful?