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Winter 2014-2015 Review and Verification

We made it! We can finally safely say that the winter season is over and, while the cold seems to want to endlessly stick around, Spring is strengthening its grasp. Now that the days of snow and bitter cold are over, we’ve compiled a detailed review of the brutal winter as well a verification for our winter forecast we issued back in early November.

Some highlights of this winter include:

1) The second coldest February on record, with widespread ice buildup on the Hudson River.

2) Winter storm “Juno” in late January which gave parts of eastern Long Island over two feet of snow.

3) A persistent cold and snowy pattern from late January through March, with an active assault of moderate snow events — somewhat reminiscent of last year’s winter.

4) Boston’s snowiest winter on record.

In our review, we break down the winter month-by-month and provide temperature departures and snowfall amounts for Central Park, as well as descriptors and verification statistics.

December: 

Average Monthly Temperature: 40.5 F

Departure from Average: +3.0 F

Snowfall: 1.0″

December, 2014 was quite the warm month for the entire Northeast (HPRCC).

December, 2014 was quite the warm month for the entire Northeast (HPRCC).

What winter? That’s how December, 2014 felt for most of the Northeast. While it wasn’t historically warm, the +3.0 departure is still significant, and the month was persistently mild with no Arctic intrusions. In fact, November, 2014 had a colder minimum temperature than December, 2014. On December 1st, NYC had a high of 65 degrees, on Christmas Eve, we had a high of 58 degrees, and on Christmas Day, we had a high of 62 degrees. The only day we saw snow on was December 10th, as a large nor’easter, which originally gave the area almost 3″ of rain, stalled off the coast and became an upper-level cutoff low, rotating and bringing the area snow showers. NYC recorded an inch of snow from this event — it’s grand total for the month.

Not only was December, 2014 warm in the Northeast, but it was warm nationally as well. (ESRL)

Not only was December, 2014 warm in the Northeast, but it was warm nationally as well. (ESRL)

Not only was December warm in the Northeast, but it was warm across most of the country. The Arctic Air source was cut off and remained close to the North Pole. Often, December features more amplified ridges and troughs which aid in the southward propagation of arctic air. Instead, we had a zonal mid level atmospheric pattern, where there are very few dips in the jet stream and any chilly air has Pacific origins, as opposed to Arctic origins. The image below is a composite of the 500mb height anomalies in December, 2014. The positive 500mb height anomalies were located in Canada, and the strongest anomalies were just to our north. This allowed warm air to surge northward from time-to-time. Additionally, when the highest heights are in Canada and relatively lower heights are located to the south, the higher heights serve as a “wall” so to speak, somewhat reminiscent of a blocking pattern. This means that when storms approached our area, they slowed down and at times cut off from the jet stream. Considering the already mild airmass, this is why we had several bouts of heavy rain.

The 500mb pattern in December, 2014 was generally very zonal, with no large ridges or troughs in the United States. There was ridging at times to our north in Canada, which helped promote cutoff lows that brought heavy rain to the region.

The 500mb pattern in December, 2014 was generally very zonal, with no large ridges or troughs in the United States. There was ridging at times to our north in Canada, which helped promote cutoff lows that brought heavy rain to the region.

What prevented the area from having much more substantial warmth was the fact that the core of the strongest positive height anomalies were located just to our north. This allowed surface high pressure systems to develop there from time-to-time, which brought northerly winds. This often muted big warmups in an otherwise warmer than normal airmass.

Forecast Verification: Our forecast for December 2014 featured a quiet, zonal pattern and lack of high latitude blocking during the first half of the month. For the first 15-20 days of the month, we were correct in our ideas. However, our forecast featured a pattern transition to colder and stormier with snow chances increasing by the holidays. This ended up being too quick — as the hemispheric pattern change would wait until January.

January: 

Average Monthly Temperature: 29.7 F

Departure from Average: -2.7 F

Snowfall: 16.9″

January, 2015 saw a much different pattern from December, as cold air became the story in the Northeast, as well as a few snow events to end the month

January, 2015 saw a much different pattern from December, as cold air became the story in the Northeast, as well as a few snow events to end the month (HPRCC).

Towards the end of December and the beginning of January, there was a large shift in the hemispheric weather pattern. This allowed for much more frequent cold air intrusions in the Northeast of Arctic origins. Initially, we didn’t necessarily see the results in terms of snowfall, but instead our area was settled into a “cold-clipper” pattern, where weak waves of energy approached the area originating in Alberta, Canada and dropped light snow in the cold airmass.

In NYC, seven days saw a high temperature below freezing, and two days had low temperatures in the single digits. An inch of snow fell from a clipper system on January 6th, and temperatures dropped to the single digits the next morning — signaling the fact that winter had finally arrived and it was here to stay. A few locations had a bit more snow.

On January 9th, another clipper system trekked well to our north, which brought southerly winds from a cold front. Normally, these setups favor rain in the area, but the airmass was so cold that we still got snow — it was equivalent to a squall line of thunderstorms in the summer, except this time, with snow. A quick burst of 1.5″ fell in NYC, but parts of Queens and Nassau County saw around 2″.

Still, though, there was not a whole lot to write home about in the snowfall department, and many forecasters became worried that the initially very cold and snowy predictions for this winter would not come to fruition. We stayed the course, however, and as the pattern kept evolving towards late January, we quickly became happy with our decision.

January, 2015 was quite cold in most of the Northeast, but was just as anomalously mild in the western half of the US. This was because of strong ridging in this area, and once that established itself, cold and snow became the story in the Northeast (ESRL).

January, 2015 was quite cold in most of the Northeast, but was just as anomalously mild in the western half of the US. This was because of strong ridging in this area, and once that established itself, cold and snow became the story in the Northeast (ESRL).

The picture nationally shows that while it was very cold in the Northeast, it was extremely warm in the western half of the country. This was because of a large hemispheric pattern shift in the eastern Pacific and western half of the US from zonal, to having persistently very strong ridging.

January, 2015 saw quite the change at 500mb compared to December, 2014. Large ridging was located in Alaska and the western half of the US, which allowed for Arctic air to slide down to the Northeast.

January, 2015 saw quite the change at 500mb compared to December, 2014. Large ridging was located in Alaska and the western half of the US, which allowed for Arctic air to slide down to the Northeast (ESRL).

The core of the strongest ridging was located in Alaska and in the western half of the US. The ridging in Alaska is what helps to dislodge the Arctic air from that region and send it southward, while the ridging in the western half of the US allows that Arctic air to get displaced in the Northeast, instead of areas further west. This was actually similar to the feature which gave us the cold last winter — once we saw the similarities developing, we knew we had a major shift to winter on our hands. The ridging in the western US would sometimes link with the Alaskan ridging, helping to produce intensely strong Arctic outbreaks.

This tandem ridging would eventually help turn our pattern to a snowy one. This is part of a +PNA pattern, where there is a ridge in the west and a trough in the east. What often gives the area snow events is a “spike” in this ridging, or a “PNA spike”. In late January, we saw a very strong spike in this ridging, which allowed for potent disturbances to dive down from Canada, deep into the United States. This gave the area a moderate snow event on January 24th, where 3.6″ of snow fell in NYC, and several inches more in interior locations. It also set the table a few days later for a much stronger disturbance to slide down from Canada and amplify in the Tennessee Valley, while another disturbance formed in its heels — equivalent to several kids in a row going down a slide in a playground. When these two disturbances phased together, we had winter storm “Juno” on January 26-27.

Despite not living up to its hype, the Janaury 26-27 winter storm still brought very impressive snow totals for much of the region (National Weather Service, Upton, NY).

Despite not living up to its hype, the Janaury 26-27 winter storm still brought very impressive snow totals for much of the region (National Weather Service, Upton, NY).

While this storm ultimately didn’t live up to expectations in NYC, it still brought just under 10″ of snow to Central Park, 10-12″ of snow in Queens, 12-18″ of snow in Nassau and western Suffolk Counties, and 18-30″ in eastern Suffolk County. Most of New Jersey saw between 5-10″ of snow. All-of-a sudden, winter’s grasp was becoming permanent, and we were quickly making up for lost ground in the snow department. This would continue into February, which saw one of the coldest months ever recorded in the Northeast.

Forecast Verification: January turned out to be a spectacular month for our winter forecast, which called for a pattern change as well as colder than normal and snowier than normal conditions.

February: 

Average Monthly Temperature: 23.9 F

Departure from Average: -11.4 F

Snowfall: 13.9″

February, 2015 was one of the coldest months ever recorded throughout the Northeast. Most locations were between 10 and 20 degrees below average! (HPRCC)

February, 2015 was one of the coldest months ever recorded throughout the Northeast. Most locations were between 10 and 20 degrees below average! (HPRCC)

The pattern that was developing in January took a more extreme turn in February, as frequent Arctic assaults hit the Northeast. It was as if we were in another climate regime — putting last winter’s cold to shame. The snow from “Juno” never completely melted, as we started building a large snowpack.

We began the month with 5″ of snow on February 2nd, though isolated parts of Long Island saw a lot more than that. A storm attempted to take a track that would often give rain to the region, to our north and west, but there was so much Arctic air locked in to our north that the storm transferred its energy to the south much quicker than forecast. Instead of heavy rain washing away the snow, most areas had temperatures staying in the low 20s with freezing rain, creating lots of ice. Then as the new transferred coastal storm strengthened, bands of very heavy snow developed on the back side of the storm, creating whiteout conditions and leaving the rush-hour commute to an absolute stand-still. Long Island received 2-3″/hour snowfall rates, and 3-6″ total on the back-side of the storm alone. It was a 3-4″ snowfall on the front-end, then freezing rain, then a heavy band of snow on the back-end, bringing 6-10″ snowfall totals in many locations. This created a large snowpack with an icy layer in the middle, and the bitter cold assured that it would stick around.

February, 2015 saw historic cold in the Eastern US, but historic warmth in the Western US. The scale at the bottom tells the story very well. (ESRL)

February, 2015 saw historic cold in the Eastern US, but historic warmth in the Western US. The scale at the bottom tells the story very well. (ESRL)

Some impressive stats for the month (for New York City, unless otherwise indicated):

1) There were seven single-digit low temperatures this month, all occurring in a twelve-day period. The lowest temperature was 2 degrees on the morning of February 20th, which shattered the daily record of 7 degrees, back in 1950.

2) 15 out of 28 days of that month had high temperatures at freezing or below.

3) There was only one day during the entire month where temperatures were above average. This occurred on February 22nd, where 1″ of snow fell on that morning after 3″ of snow fell during the prior night. So, we had 27 below-average days, and the other day started off as a winter wonderland. That day had a high of 43 degrees, which not only was the highest temperature all month, but also the highest temperature in the entire January 6th through March 3rd period.

4) It was the second coldest February ever recorded, with only February, 1934 being colder.

5) It was the coldest month ever recorded in Hartford, CT, Worester, MA, and Syracuse, NY, among many other locations in the New England area. Syracuse, NY had an average monthly temperature of 9 degrees, which is 16.9 degrees below average!

With the frequent Arctic outbreaks came several light to moderate snow events, including 3-4″ of very fluffy snow during the overnight of February 17th. In “normal” snow situations, the snow to liquid ratio is around 10:1, which means that 10″ of snow would melt down to 1″ of rain. But this snow was so fluffy (as opposed to wet) that it had a snow to liquid ratio of around 25:1.

February, 2015 featured extremely strong ridging in Alaska, which helped to dislodge Arctic air in historic proportions (

February, 2015 featured extremely strong ridging in Alaska, which helped to dislodge Arctic air in historic proportions (ESRL)

While there were plenty of similarities to the pattern in January and February, February had stronger ridging in Alaska, which helped Arctic air to plunge southward even more readily. There was also a more direct connection between the ridge in the west and the ridge in Alaska, which assured that the Arctic air would always plunge towards our area. The negative height anomalies with the trough in the Northeast were simply remarkable. Once again, though, the heights in Greenland were low, indicating more in the way of a +NAO. This is what prevented our area from having a major blizzard. However, since the heights remained low in those regions, widespread cold was able to sustain itself in those regions, and when combined with the extremely anomalous ridging in Alaska, that cold air source readily slid southward. In some of the past winters with stronger Greenland blocking (2009-2010, for example), it was a consistently cold winter, but the Arctic air was not as harsh, since the higher heights in Greenland modified one of our sources of Arctic air. Had the ridging in Alaska not been so anomalous, February, and other months of this winter would not have been nearly as snowy as they turned out.

Forecast Verification: Our winter forecast verified very well during the month of February, but some aspects did not pan out as forecast. For instance, while the month was colder and snowier than normal — as we anticipated — we did not see the high latitude blocking which we thought would occur. Accordingly, the “blockbuster” event potential didn’t come to fruition. The lack of blocking to slow down the pattern meant that the bigger events kept hammering New England.

For the most part, this pattern continued into March, but a few subtle adjustments allowed for a bit more snow than in February.

March: 

Average Monthly Temperature: 38.1 F

Departure from Average: -4.4 F

Snowfall: 18.6″

March, 2015 continued the theme of very cold weather across the Northeast (HPRCC).

March, 2015 continued the theme of very cold weather across the Northeast (HPRCC).

Right off the bat, NYC saw 4.8″ of snow on March 1st, in another setup that really had no business giving us that much snow. In most winter airmasses, this storm would have given the area rain and sleet, since the storm tracked to our north, but instead we got snow because of the Arctic airmass  in place. One of the major themes of the month was above normal temperatures in the Southeast, and below average temperatures in our area and especially in SE Canada — creating a stronger than average temperature gradient. This helped precipitation to blossom in the form of snow.

After a brief warmup to 45 degrees on March 4th along with a bit of rain, the ingredients began developing into a snowstorm that everyone likely remembers. A cold front on the leading edge of more Arctic air was approaching the region, and multiple waves of energy rode along this front. Initially, precipitation started as rain. However, as the cold front crossed, temperatures plummeted through the 30s and into the 20s. Due to the southeast ridging, the front stalled just to our south, so the waves of energy were still very close to our region — this time in a much colder airmass. This occurred with an incredibly strong jet stream just to our north, aiding in periods of moderate to heavy snow all day on March 5th. It started off as a wet snow, clinging to the trees and bushes, but then became a fine powder with textbook snowflakes that blanketed the region with 6-9″ of snow. NYC saw 7.5″ from this storm.

Once again, the national picture shows lots of warmth in the west and plenty of cold in the Northeast. There was a bit more warmth in the Southeast, due to some ridging in that area (HPRCC).

Once again, the national picture shows lots of warmth in the west and plenty of cold in the Northeast. There was a bit more warmth in the Southeast, due to some ridging in that area (HPRCC).

After the 7.5″ of snow, the temperature fell to 12 degrees in NYC, and we recorded a 19″ snow-depth on the morning of March 6th. The temperatures slowly warmed up a bit, as we lost some of the Alaskan ridging that had been supplying us with Arctic air. We finally hit a high of 59 degrees on March 11th, but then the wintry pattern reloaded on March 18th, as another cold front came through the region. While the Arctic air was somewhat modified, we had enough cold air for yet another snow event on March 20th, the first day of Spring. This was a classic wet-snow event, as heavy wet snow clung to trees and bushes, creating a beautiful wintry scene. 4.5″ of snow fell in NYC, though some locations had as much as 5-6″ of snow. The stronger March sun angle initially meant the snow didn’t stick to the warmer roads, but as we lost solar heating, the snow eventually stuck to the roads as well.

A snowy first day of Spring in Rockville Centre, NY (Doug Simonian).

A snowy first day of Spring in Rockville Centre, NY (Doug Simonian).

The chilly air stuck around after this storm, but due to the strong March sun angle, the snow melted quickly. March 28th saw a light snow event — snow fell but didn’t accumulate in most areas, parts of Suffolk County picked up several inches of snow with coatings and dustings in Nassau County and Queens. On March 30-31, there was a light rain storm, but it mixed with and changed to snow in parts of the region. New Jersey had minor accumulations, but only a trace of snow was recorded in NYC. After that, we were finally — FINALLY — done.

March, 2015 saw plenty of ridging in the western half of the US and plenty of troughing in SE Canada. Some ridging built in the SE US, which led to a strong temperature gradient -- combine that with the ridge out west, and you have a good recipe for more snow (ESRL).

March, 2015 saw plenty of ridging in the western half of the US and plenty of troughing in SE Canada. Some ridging built in the SE US, which led to a strong temperature gradient — combine that with the ridge out west, and you have a good recipe for more snow (ESRL).

The hemispheric pattern had plenty of similarities to what we had been seeing all winter — lots of ridging in the West with plenty of cold air available in SE Canada. The trough wasn’t as deep in March compared to January and February, since there wasn’t as much ridging as a whole in Alaska. This is why it wasn’t quite as anomalously cold and why we were able to thaw out a bit in the middle of the month. But plenty of ridging in the West that poked into western Canada and Alaska still allowed for that bitterly cold air in SE Canada to plunge southward, creating -4 to -6 temperature departures for the month. The negative height anomalies in SE Canada and the positive height anomalies/ridge in the Southeast explains the strong temperature gradient that ignited our three snow events.

Winter as a whole (December through March):

Average Temperature: 33.1 F

Departure from Average: -3.9 F

Snowfall: 50.4″ (The average is 24 to 28″, depending on the time period you use)

Winter 2013-2014 as a whole (December through March):

Average Temperature: 34.2 F

Departure from Average: -2.8 F

Snowfall: 57.4″

Forecast Verification: One day, our forecasters will likely look back at this forecast with wide eyes of joy. But for now, we’ll nitpick the things that bother us about it — the things that didn’t come to fruition as we thought they would. Namely, the high latitude blocking and stratospheric warming event to kick it off. In the end, enhanced solar activity helped to tighten the stratospheric vortex during the month of December. While a stratospheric warming event did eventually occur, it wasn’t as strong and sudden as we anticipated.

The hemispheric pattern that developed never quite allowed high latitude blocking to lock in to place over the Atlantic and Greenland. While we did see a tremendous amount of ridging on the West Coast into British Columbia and Alaska, we never saw the same ridging over Greenland and Northern Canada. Without that ridging there, we couldn’t slow down the pattern enough to get “the big one”. The lack of blocking allowed Juno to remain slightly progressive — and also was a major part in keeping the pattern generally progressive throughout the winter. New England was able to benefit despite the lack of a blocking pattern due to their latitude and longitudinal differences.

These details are why most of this winter was very cold with several moderate snow events (what actually happened), as opposed to a bit less cold (but still cold) with a large snow event (what we forecast).

Still, this winter forecast will be looked at as a great success. Our forecast for colder, snowier than normal conditions worked out well. While the blocking didn’t work out, the pattern in the Pacific played out mostly as forecast. This allowed for the progression of winter getting colder and snowier as it went on — with February being the coldest month — to work out very well. And some people in our forecast area (Long Island) still did get a major to historic snowstorm in Juno, so our signaling the potential for a big event somewhat verified.

Regardless of specifics, this winter will remembered as one of the “Great ones” in New York, New Jersey, and Connecticut — and especially into New England. The tremendous amount of cold and snow, and historically persistent snow, won’t be soon forgotten.

Thank you all for following along with us during this special winter.

We’ll be back at it sooner than you can say “Summer”.

 

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