I’ll start out by saying this is a time of year that many around the community look forward to. November 1st marks the Daylight Saving Time change where model guidance begins to come in earlier, the sun sets earlier, and the average temperatures drop almost as fast as the leaves around the neighborhood. That said, there is a lot of hype this time of year as well and I think it’s prudent for us to all take a step back and take a more objective look at everything that’s going on around us, and what it could mean for the upcoming season. I’ve considered a large array of factors in my 2009-2010 winter forecast. Some of these factors (not all) are included below:
The El Nino Southern Oscillation (ENSO), The North Atlantic Oscillation (NAO), The Pacific North-American Index (PNA), the East-Pacific Oscillation (EPO), The Arctic Oscillation (AO), The Pacific Decadal Oscillation (PDO), snow cover, trends amongst both the climate over the past several years and this year, and the more recent pattern progression over the past few seasons, SST (Sea Surface Temperatures) and anomalies, and Atlantic and Pacific ocean pattern progression. As mentioned above, other factors were included (example: soil moisture) but to a lesser extent than those listed above.
This outlook will be broken down into three separate sections: Where we stand, What could change, and What is expected. Where we stand will analyze everything that is pretty much known, or is a given at this point. What could change will analyze, in detail, some of the more uncertain factors that could change and lead to differing results this winter. What is expected will sum up the above two sections and finalize the winter forecast.
Where We Stand
At this stage in the game, there are many more “certains” then just a few weeks ago. This is why I figured it would be a smart decision to wait until November to issue this winter forecast. I’ve included a map below displaying the latest SST (Sea Surface Temperature) Anomaly map from the week of October 25, 2009. This is a week or so old, but it’s meant to illustrate a general point and, all things considered, not much has changed dramatically since then. There’s obviously a notable Nino event ongoing, and it’s likely to continue through the winter. Whether or not it strengthens dramatically over the next month will obviously have some impact on the pattern, but the general idea is that the Nino will be at low end-moderate levels, or possibly near mid-moderate levels. There have been about 56,000 CONUS temperature and precipitation departure composite maps posted for moderate-nino events, so I am sure you can find one somewhere. The bottom line is this: almost all of them featured above average precipitation in the Eastern half of the CONUS, and the sub-tropical jet stream is the culprit. Moderate Nino events featuring basin-wide above average departures and west-based/warm water near the date-line are notorious for featuring favorable tropical forcing and strong sub-tropical jet streams. The image to the left details the basin-wide impact of the event, as well as the strengthening of the west based above average departures.
To further detail the progression of the basin event and, specifically, the strengthening in the far west portion of the basin I’ve included a 17 slide animation of weekly readings since July 2009. This helps illustrate the point being made by many on the forums over the past few weeks: the event is still strengthening, and has become notably warm especially on the western fringe. There are a few culprits for this occurrence, but most notable are the trade winds and sinking SOI over the recent weeks. Additionally, sub-surface water temperatures upwards of 4 C are present, again making this a notable event.
Click here for loop
The forecast guidance envelope for ENSO forecasts have tightened somewhat, but are still lagging a bit. Still, most guidance peaks this event at near moderate-strength, followed by a slow decrease in strength towards the end of the winter. This seems reasonable at this time.
Again using the SSTA maps above, we can draw some more conclusive evidence/ideas. The PDO is a major player when forecast correctly in conjunction with the ENSO state and several other indices. You can CLICK HERE for an image (trying not to clog up the thread with a million images) which displays the SST correlation for a positive and negative PDO phase. Currently, the PDO is in limbo a bit if we take a look at the SSTA map mentioned above. There are definitely some expanding negative departures, but they are not based/expanding far enough to the west to be defined as a substantial positive PDO. The raw data does agree here as we see the PDO trending towards neutral. Generally, a positive PDO will feature higher heights and a mean ridge over Western North America, while a mean trough is established over Eastern North America. A Negative PDO phase is generally opposite.
August PDO Value: -1.39 September PDO Value: -0.30
The image below above to the left details the PDO forecast, which is expected to rise from near neutral into a slightly positive state, and peak at around .6 (positive) value near the 4-5 month lead time, before decreasing again toward neutral several months from now. Again, my general idea for the PDO is neutral to around +.50 for this winter.
The NAO State remains a complicated one to forecast with significant lead time. Long range forecast is still new to me, so it’s been something I have been working to grasp. A general analysis of the fall pattern can, and has become, a very good indicator towards the NAO in the following winter. Specifically, there seems to be a developing inverse correlation between October NAO values and the general winter NAO following. Included below are several examples of this inverse correlation
1951-52: October – positive, DJFM – negative
1957-58: October – positive, DJFM – negative
1963-64: October – positive, DJFM – negative
1965-66: October – positive, DJFM – negative
1976-77: October – positive, DJFM – negative
1977-78: October – positive, DJFM – negative
1982-83: October – negative, DJFM – positive
1986-87: October – positive, DJFM – negative
1997-98: October – negative, DJFM – positive
2002-03: October – negative, DJFM – positive
2004-05: October – negative, DJFM – positive
2006-07: October – negative, DJFM – positive
This October, the NAO observations were negative, and then neutral/negative towards the end of the month. This doesn’t provide many definite answers, but the general feeling is the NAO state will be neutral or potentially slightly positive this winter as a whole. The AO (Arctic Oscillation) is a major mode of circulation variability in the Arctic and North Atlantic. As defined by NSIDC “The oscillation exhibits a "negative phase" with relatively high pressure over the polar region and low pressure at mid latitudes (about 45 degrees North), and a "positive phase" in which the pattern is reversed. In the positive phase, higher pressure at mid latitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general "opposite" to those of the positive phase”. A quick analysis of nino years reveals that the Arctic Oscillation was negative nearly 80% (14 of 18 or 78%) of the time. A notable signal to say the least. The arctic oscillation forecast is included below, note the prolonged period of negative readings and ensemble forecasts already featuring negative readings into the coming weeks.
The QBO (Quasi-Biennial Zonal Wind Oscillation) can work hand in hand in determining the pattern around these previous AO readings and associated winter patterns. The QBO can be generally hard to define for those trying to gain an understanding of how it works and what it is, but a few forecasters on this forum have put it very well. Generally, the QBO is a stratospheric wind anomaly that can play an important role in seasonal/long range forecasting. The wind fields oscillate from easterly to westerly in the tropical stratosphere. Easterly phase/negative QBO years feature more promoted height fields and more robust high latitude blocking (in turn promoting more frequent –AO), while the Westerly Phase/Positive QBO tends to promote less favorable conditions for high latitude blocking. The correlation between the –QBO and –AO is somewhat marginal, but of the past 59 years, 10 of 15 years with a moderate to strong –QBO also featured a –AO average over DJF. Currently, the QBO is moderately negative, adding reinforcement for a –AO forecast this DJF.
What Can Still Change
This section is still pretty broad because, well, everything can still change. Generally this section of the outlook is meant to detail some things that still aren’t certain and could have a big impact on the forecast this winter. Snow cover is (and probably will remain for all winter outlooks to come) one of these factors. I’ve included a snow cover map to the left from November 1, 2009 (the latest map available off the NOAA site). What’s more important than the actual image below is the progression of the snow cover itself. This year, it’s very encouraging. The snow cover over Eurasia and Northern Canada has increased so dramatically over the past several weeks that it’s beginning to approach levels comparable to 2002 (one of the “benchmarks” for extremely favorable snow cover levels). Snow cover remains a broad factor to be included in winter forecasts, as it doesn’t really have any straight forward impacts. However, some of the better winters on record have featured above average snow cover towards the end of fall. Comparatively, some of the warmer/less snowy winters in the east have featured minimal snow cover. To compare, we are well ahead of the snow cover observed in 2008.
The pattern over the past few months and through this autumn also fits very well into this section, and a brief reanalysis of the pattern itself can often lead to clues into the upcoming winter. This autumn has featured below normal temperatures through October (a generally good signal for a below normal average DJF through the eastern us) and above average precipitation across much of the South/Southeast. This anomalous precipitation was mentioned above as a result of the increasingly active sub tropical jet, also favorable through the winter. This fall has featured a quick influx of STJ driven Miller-A type systems, which we have lacked significantly over the past few winters. The active southern stream storm track has lead to a few coastal storms as well as a few storms which cut northwest into the Appalachians/Great Lakes. A quick re-analysis of the pattern will reveal why the storms cut northwest : lack of blocking to the north of the system as a result of a pattern re load and /or temporarily unfavorable pattern aloft. However, there have been plenty of favorably positioned high pressure systems this fall in Southeast Canada, which have lead to storm tracks that would have been very favorable for many in the winter season. This fall, below normal temperature anomalies have been centered over the Central US with the mean trough remaining there for the past few weeks.
What To Expect
The best way to put all of this information forward is to sum up the general index forecast for the upcoming months, which features:
Moderate El Nino
+PDO
+PNA
-EPO
-AO
+/- NAO
Analog Years: 2002-2003, 1965-1966
I expect this winter to be one of the coldest winters since the early 2000’s, and I am almost certain it will be the coldest winter since 2003-2004, especially given the lackluster cold in almost all winters since then. I’m expecting December to average above normal, but a transition towards much colder and below-normal departures for January and February, with late January into February likely featuring well-below normal cold across much of the east. I expect well above normal precipitation across most of the Southeast, Mid-Atlantic and Northeast with an active sub-tropical jet and southern stream energy. I expect multiple chances for dynamic nor-easters and Miller-A systems with significant phasing potential, specifically around the time of the pattern change in late December/early January. Generally, snowfall should average upwards of 125% over much of the Eastern US. I’ve included my forecast for the NYC area below.
Temperatures
Dec: +1 to +3
Jan : -1 to -3
Feb: -2 to -4
Precipitation: Above Normal:
Snowfall: 35-40”
The El Nino Southern Oscillation (ENSO), The North Atlantic Oscillation (NAO), The Pacific North-American Index (PNA), the East-Pacific Oscillation (EPO), The Arctic Oscillation (AO), The Pacific Decadal Oscillation (PDO), snow cover, trends amongst both the climate over the past several years and this year, and the more recent pattern progression over the past few seasons, SST (Sea Surface Temperatures) and anomalies, and Atlantic and Pacific ocean pattern progression. As mentioned above, other factors were included (example: soil moisture) but to a lesser extent than those listed above.
This outlook will be broken down into three separate sections: Where we stand, What could change, and What is expected. Where we stand will analyze everything that is pretty much known, or is a given at this point. What could change will analyze, in detail, some of the more uncertain factors that could change and lead to differing results this winter. What is expected will sum up the above two sections and finalize the winter forecast.
Where We Stand
At this stage in the game, there are many more “certains” then just a few weeks ago. This is why I figured it would be a smart decision to wait until November to issue this winter forecast. I’ve included a map below displaying the latest SST (Sea Surface Temperature) Anomaly map from the week of October 25, 2009. This is a week or so old, but it’s meant to illustrate a general point and, all things considered, not much has changed dramatically since then. There’s obviously a notable Nino event ongoing, and it’s likely to continue through the winter. Whether or not it strengthens dramatically over the next month will obviously have some impact on the pattern, but the general idea is that the Nino will be at low end-moderate levels, or possibly near mid-moderate levels. There have been about 56,000 CONUS temperature and precipitation departure composite maps posted for moderate-nino events, so I am sure you can find one somewhere. The bottom line is this: almost all of them featured above average precipitation in the Eastern half of the CONUS, and the sub-tropical jet stream is the culprit. Moderate Nino events featuring basin-wide above average departures and west-based/warm water near the date-line are notorious for featuring favorable tropical forcing and strong sub-tropical jet streams. The image to the left details the basin-wide impact of the event, as well as the strengthening of the west based above average departures. To further detail the progression of the basin event and, specifically, the strengthening in the far west portion of the basin I’ve included a 17 slide animation of weekly readings since July 2009. This helps illustrate the point being made by many on the forums over the past few weeks: the event is still strengthening, and has become notably warm especially on the western fringe. There are a few culprits for this occurrence, but most notable are the trade winds and sinking SOI over the recent weeks. Additionally, sub-surface water temperatures upwards of 4 C are present, again making this a notable event.
Click here for loop
The forecast guidance envelope for ENSO forecasts have tightened somewhat, but are still lagging a bit. Still, most guidance peaks this event at near moderate-strength, followed by a slow decrease in strength towards the end of the winter. This seems reasonable at this time.
Again using the SSTA maps above, we can draw some more conclusive evidence/ideas. The PDO is a major player when forecast correctly in conjunction with the ENSO state and several other indices. You can CLICK HERE for an image (trying not to clog up the thread with a million images) which displays the SST correlation for a positive and negative PDO phase. Currently, the PDO is in limbo a bit if we take a look at the SSTA map mentioned above. There are definitely some expanding negative departures, but they are not based/expanding far enough to the west to be defined as a substantial positive PDO. The raw data does agree here as we see the PDO trending towards neutral. Generally, a positive PDO will feature higher heights and a mean ridge over Western North America, while a mean trough is established over Eastern North America. A Negative PDO phase is generally opposite.August PDO Value: -1.39 September PDO Value: -0.30
The image below above to the left details the PDO forecast, which is expected to rise from near neutral into a slightly positive state, and peak at around .6 (positive) value near the 4-5 month lead time, before decreasing again toward neutral several months from now. Again, my general idea for the PDO is neutral to around +.50 for this winter.
The NAO State remains a complicated one to forecast with significant lead time. Long range forecast is still new to me, so it’s been something I have been working to grasp. A general analysis of the fall pattern can, and has become, a very good indicator towards the NAO in the following winter. Specifically, there seems to be a developing inverse correlation between October NAO values and the general winter NAO following. Included below are several examples of this inverse correlation
1951-52: October – positive, DJFM – negative
1957-58: October – positive, DJFM – negative
1963-64: October – positive, DJFM – negative
1965-66: October – positive, DJFM – negative
1976-77: October – positive, DJFM – negative
1977-78: October – positive, DJFM – negative
1982-83: October – negative, DJFM – positive
1986-87: October – positive, DJFM – negative
1997-98: October – negative, DJFM – positive
2002-03: October – negative, DJFM – positive
2004-05: October – negative, DJFM – positive
2006-07: October – negative, DJFM – positive
This October, the NAO observations were negative, and then neutral/negative towards the end of the month. This doesn’t provide many definite answers, but the general feeling is the NAO state will be neutral or potentially slightly positive this winter as a whole. The AO (Arctic Oscillation) is a major mode of circulation variability in the Arctic and North Atlantic. As defined by NSIDC “The oscillation exhibits a "negative phase" with relatively high pressure over the polar region and low pressure at mid latitudes (about 45 degrees North), and a "positive phase" in which the pattern is reversed. In the positive phase, higher pressure at mid latitudes drives ocean storms farther north, and changes in the circulation pattern bring wetter weather to Alaska, Scotland and Scandinavia, as well as drier conditions to the western United States and the Mediterranean. In the positive phase, frigid winter air does not extend as far into the middle of North America as it would during the negative phase of the oscillation. This keeps much of the United States east of the Rocky Mountains warmer than normal, but leaves Greenland and Newfoundland colder than usual. Weather patterns in the negative phase are in general "opposite" to those of the positive phase”. A quick analysis of nino years reveals that the Arctic Oscillation was negative nearly 80% (14 of 18 or 78%) of the time. A notable signal to say the least. The arctic oscillation forecast is included below, note the prolonged period of negative readings and ensemble forecasts already featuring negative readings into the coming weeks.
The QBO (Quasi-Biennial Zonal Wind Oscillation) can work hand in hand in determining the pattern around these previous AO readings and associated winter patterns. The QBO can be generally hard to define for those trying to gain an understanding of how it works and what it is, but a few forecasters on this forum have put it very well. Generally, the QBO is a stratospheric wind anomaly that can play an important role in seasonal/long range forecasting. The wind fields oscillate from easterly to westerly in the tropical stratosphere. Easterly phase/negative QBO years feature more promoted height fields and more robust high latitude blocking (in turn promoting more frequent –AO), while the Westerly Phase/Positive QBO tends to promote less favorable conditions for high latitude blocking. The correlation between the –QBO and –AO is somewhat marginal, but of the past 59 years, 10 of 15 years with a moderate to strong –QBO also featured a –AO average over DJF. Currently, the QBO is moderately negative, adding reinforcement for a –AO forecast this DJF.
What Can Still Change
This section is still pretty broad because, well, everything can still change. Generally this section of the outlook is meant to detail some things that still aren’t certain and could have a big impact on the forecast this winter. Snow cover is (and probably will remain for all winter outlooks to come) one of these factors. I’ve included a snow cover map to the left from November 1, 2009 (the latest map available off the NOAA site). What’s more important than the actual image below is the progression of the snow cover itself. This year, it’s very encouraging. The snow cover over Eurasia and Northern Canada has increased so dramatically over the past several weeks that it’s beginning to approach levels comparable to 2002 (one of the “benchmarks” for extremely favorable snow cover levels). Snow cover remains a broad factor to be included in winter forecasts, as it doesn’t really have any straight forward impacts. However, some of the better winters on record have featured above average snow cover towards the end of fall. Comparatively, some of the warmer/less snowy winters in the east have featured minimal snow cover. To compare, we are well ahead of the snow cover observed in 2008. The pattern over the past few months and through this autumn also fits very well into this section, and a brief reanalysis of the pattern itself can often lead to clues into the upcoming winter. This autumn has featured below normal temperatures through October (a generally good signal for a below normal average DJF through the eastern us) and above average precipitation across much of the South/Southeast. This anomalous precipitation was mentioned above as a result of the increasingly active sub tropical jet, also favorable through the winter. This fall has featured a quick influx of STJ driven Miller-A type systems, which we have lacked significantly over the past few winters. The active southern stream storm track has lead to a few coastal storms as well as a few storms which cut northwest into the Appalachians/Great Lakes. A quick re-analysis of the pattern will reveal why the storms cut northwest : lack of blocking to the north of the system as a result of a pattern re load and /or temporarily unfavorable pattern aloft. However, there have been plenty of favorably positioned high pressure systems this fall in Southeast Canada, which have lead to storm tracks that would have been very favorable for many in the winter season. This fall, below normal temperature anomalies have been centered over the Central US with the mean trough remaining there for the past few weeks.
What To Expect
The best way to put all of this information forward is to sum up the general index forecast for the upcoming months, which features:
Moderate El Nino
+PDO
+PNA
-EPO
-AO
+/- NAO
Analog Years: 2002-2003, 1965-1966
I expect this winter to be one of the coldest winters since the early 2000’s, and I am almost certain it will be the coldest winter since 2003-2004, especially given the lackluster cold in almost all winters since then. I’m expecting December to average above normal, but a transition towards much colder and below-normal departures for January and February, with late January into February likely featuring well-below normal cold across much of the east. I expect well above normal precipitation across most of the Southeast, Mid-Atlantic and Northeast with an active sub-tropical jet and southern stream energy. I expect multiple chances for dynamic nor-easters and Miller-A systems with significant phasing potential, specifically around the time of the pattern change in late December/early January. Generally, snowfall should average upwards of 125% over much of the Eastern US. I’ve included my forecast for the NYC area below.
Temperatures
Dec: +1 to +3
Jan : -1 to -3
Feb: -2 to -4
Precipitation: Above Normal:
Snowfall: 35-40”
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