It’s been a struggle just to get the flakes flying this winter, nevermind a significant snowstorm. With the next 7-14 days likely to continue the above normal temperature regime, it’s highly unlikely the NYC metro area receives an accumulating snow event. Global teleconnectors remain unfavorable, with a similar pattern to what we saw most of this winter — low heights over the arctic and north atlantic (cold) and higher than normal heights (warm) across North America. Since the next couple weeks look shot, I thought I’d look beyond March 15th, at past weather patterns, to examine synoptic set-ups that yielded a snow event in the metro area.
March 2004 featured some moderate snows in the latter part of the month; below is the 500mb composite for that period:
We had a positive NAO, AO, but the positive PNA (western US ridging) was a major help, as well as good cold air supply in southern Canada. 850mb temperatures were well below 0c, and surface high pressure was well positioned in Quebec.
Surface air temperature anomaly for that same period – note the chill in Eastern Canada and the Northeast US:
The year prior to this, the metro area witnessed a very late season snowstorm on April 7th, 2003. Below is the 500mb pattern for that day:
Mid level riding in the Northeast and SE Canada, and check out the surface temp anomaly map – talk about some extreme negative departures:
March 15th, 1999, unlike the previous cases, had a strongly negative AO in March, and the event featured a nice 500mb block to the west of Greenland – near ideal orientation for a bomb of negative heights in the Eastern US.
The low pressure center was fairly intense, about 996mb on the mid atlantic coast, with plentiful surface cold in place; high pressure was present but not overly strong.
March 31st-April 1st 1997 was a minor event for NYC, but suburbia NJ recorded several inches to upwards of 10″ of snow in some locations. This was a major to historic snow for portions of southern New England.
Similar to our previous cases, the H5 pattern is far from the ideal that one would picture for the winter months of DJF. Positive heights in the northern latitudes, and a trough in the PAC NW. But shorter wavelengths in the spring allow an East Coast trough to be possible even w/ no Western ridge. What we did have – yet again – was mid level ridging to the N/W and thus plentiful surface high pressure, low level cold drainage into the storm system.
Surface temp anomalies — one word: Wow
April 9th-10th 1996 — a significant snow for NJ, to close out the snowiest winter on record for most. Once again, high pressure (1025mb approximately) situated to our west, plentiful cold air (850mb temps of -5c to -7c), and in this case, the most high latitude blocking we’ve seen of our cases thus far:
You’ve got a negative NAO, AO and positive PNA, negative EPO (Western US ridge, Alaska ridge) also known as the teleconnectors lined up perfectly for a significant late seaon snow event.
The surface temp anomaly – coincides nicely with the negative heights at 500mb – very cold:
March 18t, 1994, a 3-6″ snow event, had a set-up at H5 like this:
Big neg height anomalies from the PAC NW (again – generally unfavorable in winter, but not early spring) and a mid level ridge to the west of Greenland (conducive for east coast cyclogenesis)
I thought I’d examine one more, infamous Northeast late season snowstorm — April 12th, 1982 — the most significant of all late season events for NYC, with about 10″ (over a foot accumulated in NW suburbs).
The 500mb pattern, featured a PAC NW trough (low heights in the gulf of Alaska), a positive AO, and NAO probably negative. Nothing in the global teleconnectors would scream major snowfall – but in early spring, a strong West Coast trough actually teleconnects to the trough on the East Coast. Furthermore, we’ve got mid level ridging in the central US, plentiful surface cold air, and probably strong high pressure as well:
So the common denominator to all these snow events — unseasonably cold air, with mid level ridging (and surface high pressure) preferrably to the north/west of the storm. Some events had northern latitude blockings, others didn’t. Many featured a PAC NW trough and Central US ridge.
One thing we’ve seen very little of this winter in North America is unseasonably cold air – in fact we’ve had the opposite. Here’s the NAEFS week 2 forecast for the country (through March 18th):
Not a pretty look – very mild across Canada and the US, basically a repeat of the DJF pattern. If this verifies, which it should, an above normal temp regime does not bode well for late season snow events. Maybe we can see some cooling after March 20th, but I wouldn’t bet on it. Either way, the snow enthusiast can hold out hope until early-mid April for a pattern similar to one of the cases presented here. I’d say March will probably go snowless (or very close to it) in NYC. Once we make our way to the end of March, chances for accum snow fall off a cliff. But, we shall how the next several weeks play out.