Comparing Teleconnection Patterns to Historic Snowstorms

February 2019

Overview: Several cities along the East Coast of the United States are shown to compare their biggest snowstorms with the various patterns of Climate Variability. The following patterns were used:

North-Atlantic Oscillation(NAO)
Pacific-North American Pattern(PNA)
Arctic Oscillation(AO)
Pacific Decadal Oscillation(PDO)
El-Nino Southern Oscillation(ENSO)
Madden-Julian Oscillation(MJO)

The table below shows the top snowstorms for Philadelphia, PA against the various index values and phases for each pattern. Several other cities are also included and listed below the table. The data range for the snowstorm events are the months of Decemeber, January, February and March from 1950 to 2018. The colors represent the various phases of the patterns, with red being warm, blue being cold and green being neutral. The light and dark shades of color represent the strength of phase such as strong or weak. ENSO values are based using the Nino 3.4 region for weekly, monthly and 3 month running mean. Daily MJO phases prior to 1974 are not avilable. The data sources for each of the index values are provided at the bottom of this page.

Top 15 Snowstorms(Dec. to March 1950-2018) Philadelpha, P.A.
Philadlephia International Airport(KPHL)
Storm Event	Snowfall(inches)	NAO(7-day Average)	PNA(7-day Average)	AO(7-day Average)	ENSO	PDO(monthly)	MJO(daily)
January 7-8, 1996	30.7	1/2 to 1/8 = -0.925	1/2 to 1/8 = 0.245	1/2 to 1/8 = -1.644	Weak La Nina	Weak Positive	Phase 1
February 5-6, 2010	28.5	1/31 to 2/6 = -0.463	1/31 to 2/6 = 0.523	1/31 to 2/6 = -3.499	Moderate El Nino	Weak Positive	Phase 7
December 19-20, 2009	23.2	12/14 to 12/20 = -1.843	12/14 to 12/20 = 0.212	12/14 to 12/20 = -4.185	Moderate El Nino	Neutral	Phase 7 and 8
January 22-23, 2016	22.4	1/17 to 1/23 = -0.329	1/17 to 1/23 = 1.161	1/17 to 1/23 = -2.079	Very Strong El Nino	Strong Positive	Phase 2
February 11-12, 1983	21.3	2/6 to 2/12 = -0.527	2/6 to 2/12 = 0.717	2/6 to 2/12 = -2.416	Very Strong El Nino	Positive	Phase 2 and 3
February 16-17, 2003	18.7	2/11 to 2/17 = 0.789	2/11 to 2/17 = 0.487	2/11 to 2/17 = 0.202	Weak El Nino	Strong Positive	Phase 7 and 8
February 9-10, 2010	15.8	2/4 to 2/10 = -0.936	2/4 to 2/10 = 0.786	2/4 to 2/10 = -4.597	Moderate El Nino	Weak Positive	Phase 8
January 26-27, 2011	15.1	1/21 to 1/27 = -0.684	1/21 to 1/27 = 1.124	1/21 to 1/27 = -1.187	Moderate La Nina	Weak Negative	Phase 8
December 11-12, 1960	14.6	12/6 to 12/12 = -0.168	12/6 to 12/12 = 1.482	12/6 to 12/12 = -0.885	Neutral	Neutral	N/A
February 18-19, 1979	14.3	2/13 to 2/19 = -0.280	2/13 to 2/19 = -0.515	2/13 to 2/19 = -0.263	Neutral	Negative	Phase 3 and 4
February 6-7, 1978	14.1	2/1 to 2/7 = 0.116	2/1 to 2/7 = 1.011	2/1 to 2/7 = -4.494	Weak El Nino	Positive	Phase 7 and 8
January 21, 2014	13.5	2/1 to 2/7 = -0.007	2/1 to 2/7 = 1.089	2/1 to 2/7 = -1.722	Neutral	Neutral	Phase 6
January 19-20, 1978	13.2	1/14 to 1/20 = 0.529	1/14 to 1/20 = 0.240	1/14 to 1/20 = -0.032	Weak El Nino	Neutral	Phase 3 and 4
January 19-20, 1961	13.2	1/14 to 1/20 = 0.227	1/14 to 1/20 = 1.296	1/14 to 1/20 = -1.116	Neutral	Positive	N/A
February 15-16, 1958	13.0	2/10 to 2/16 = -0.513	2/10 to 2/16 = 0.794	2/10 to 2/16 = -1.725	Moderate El Nino	Weak Positive	N/A

Results for the rest of the cities.

Observations: The negative phase of the Arctic Oscillation showed the most occurances of historic snowstorms among all the patterns. Two conditions are especially important:

A moderate or strong negative phase of the pattern(all storms during the (winter of 2009/2010 and Blizzard of 1978)
A rapid/violent phase change when going from negative to positive and vice versa(January 22-23, 2016 and February 9-10, 1969 storms)

This is highly significant for Philadelphia, with the top five biggest snowstorms and 12 out of 15 during this period all occuring when these conditions are met. This city has also shown the highest signficance with the AO for monthly and seasonal snowfall through my own research. In addition, a college study I worked on back in 2004 also showed the AO to be the most significant against other climate patterns.

Several other features are also observed:

Stronger ENSO warm phases (El Nino) are more favorable for big snowstorms in Washington and Baltimore, while stronger ENSO cold phases (La Nina) are less favorable. Both cold and warm phases produce events with equal chances for all other cites.

Historic events are seen with warm, neutral or negative phases for every pattern. However, only two occurances were seen for a positive AO. This was the January 26-27, 2015 event that affected Boston and the January 15-17, 1965 even that affected Richmond. Getting a historic snowstorm for any city when the AO is moderately or highly positive is highly unlikely and caution should be used when forecasting these events. These two events would be considered 'Black Swans' as they would be anomalies away from a normal distribution.

Several storms show the dominance of having a negative AO as it offset the less favorable phases of all the other patterns. An example of this is during the Winter of 2010-2011 where a highly negative AO produced two big snow events over Philadlephia despite there being a borderline Strong La Nina.

There is a higher significance of these events occuring when the PNA was positive for Philadelphia and Baltimore.

Both President's Day snowstorms(1979 and 2003), and the December 9, 2018 and January 15-17, 1965 events for Richmond are anomalies that skewed away from the favored phase patterns for historic East Coast snowstorms. This is why it is very important to study every historic snowstorm that has occured on a synoptic scale to compare all features that allowed for such an event to occur. However, it should be noted that in all these storms, it did not produce an all snow event for these cities as sleet mixed in for several hours. Key synoptic features need to be in place for an event to be all snow and produce a record snowfall.

Boston has the least significance of all the cites as equal chances are seen during neutral, warm or cold phases for all patterns.

With the exception of Richmond, all other cites show greater occurances of seeing these events with a positive PDO, espeically during the second half of the winter season.

With the exception of Richmond, the MJO has a slight increase in these events when in phases 7 and 8.

As mentioned already, there are several occasions where many or all of the patterns were not in the ideal phase for historic US East coast snowstorms. Some of these events were also poorly forecasted and busted big time. Some examples include the January 25-26, 2000 event that was a memoriable surprise, which shifted track at the last minute. Another is the January 26-27, 2015 event where many forecasters were predicting a double digit snow for Philadelphia with a moderately +AO(+1 standard deviation or greater), even though there had only been one time since 1950 when that occured(Superstorm 1993). This also was a Miller B storm, which in some cases has a sharp cutoff of the precipitation on the western side and can destroy a forecast. One great example of this was the December 30, 2000 event, where Wilmington, DE saw very little, Philladelpha had 7" and Northern NJ had 20"+. In addition, these storms more often affect New York City to New England. Lastly, there is the December 9, 2018 event over Richmond with a moderately +NAO and neutral AO and PNA. Some forecasts were very underdone until the last minute when totals were greatly increased.

Lastly, these results don't guarantee a historic snowstorm for any one city. It is a guide and comparision to show which patterns separately or together increase the chances of seeing such an event.

Data Sources

NAO, AO, PNA
Daily --> NAO - Climate Prediction Center
          PNA - Climate Prediction Center
          AO - Climate Prediction Center

PDO
Monthly --> JISAO

ENSO 
Weekly and Monthly --> Climate Prediction Center
3-Month Running Mean--> Oceanic-Nino Index - CPC

MJO
Daily and three month running mean--> Australian Bureau of Meteorology

Snowfall
Various National Weather Services Offices--> NWS