If there’s any word for winter 2017-18, it’s ‘variable.’ We have never really gotten stuck in a pattern for too long and have seen everything from mild spells and meltdowns to ice storms and frigid cold and everything in between! The variability is a hallmark of La Nina winters, and though this one has not necessarily been a ‘typical’ La Nina the up and down nature has lived up to its reputation. And this week, we’ll get a little bit of everything as well.
Up first, some remarkable warmth. An unprecedented ridge in the upper levels has taken control of the eastern U.S. The map above shows the height of the 500mb pressure level in the atmosphere. A ‘thicker’ atmosphere is a warmer one, and a ‘thinner’ atmosphere is a colder one. For example, the depth of the troposphere is greater at the tropics than the poles. So when we look at a map like this, the higher 500mb height shows a thicker atmosphere and therefore a very warm one.
You can tell by the legend that we are in uncharted territory for these heights during the month of February. In fact, heights like these are impressive in summer. That tells us we are in for some anomalous results at ground level as well. Numerous record highs will be spread across the east on Tuesday and Wednesday. The question is – will it be all-time warmth or daily records that are broken?
On Tuesday, we set the table locally with 50s and 60s. Areas away from the South Coast have the best shot at sunshine and 60s during the afternoon. Unfortunately for the south coasters, a southwest wind is not friendly in a spring pattern. The warm air over still cold ocean water produces fog, low clouds, and lowered temps that will just barely crack 50 degrees on Tuesday and slightly warmer on Wednesday. Still mild for February, but not the big warmth that folks inland will receive.
Wednesday is the potential record day for New England. Temperatures will be peaking aloft and we will have an extraordinarily warm launching pad in the morning (temps won’t drop out of the 50s on Tuesday night). So it all comes down to sunshine. We’ll have a southwest wind, going west-southwest as the cold front approaches in the afternoon. This is ideal to maximize temperatures in the valleys…especially the Merrimack Valley and the Connecticut River Valley. Conservatively, these spots should hit 70. If we get enough sunshine during the day, mid to upper 70s are not unreasonable!
How about the city of Boston, where official records date to 1872? The all-time February record is 73 degrees, set just last year during the same week. The city has only reached 70 twice in those 146 years during February…so this is really rare air. Provided there is enough sunshine, 70 is definitely in reach and 73 is as well. It’ll all come down to how much of that sun decides to come out. The air mass certainly supports all-time potential if it stays bright. So we’ll be on record watch for sure.
We’ll also be keeping tabs on the low temperature for the day. The all-time warmest low temperature for Boston in February is 50. It’ll come down to when exactly the cold front moves through (it should be very close to midnight). But that will have a chance at being broken as well.
What does it mean for snow cover? All if it will most certainly be gone across southern New England…and a good chunk of northern New England as well. As for plants…I think we’ll be O.K. The warmth is extreme, but it is only for two days. The spring bulbs will burst…like crocus and snowdrops. But it shouldn’t be enough heat to fool and bring out the more tender vegetation like fruit tree blossoms, etc. Those cannot take the cold that will return, but the early spring bulbs can. If you tap maples you’ll definitely see quite a run of sap over the next couple of days, too.
So what follows the warmth? Reality. Cooler air will rush in on Thursday with highs in the upper 30s to mid 40s. And as a wave of low pressure rides through the area, we’ll likely get a batch of rain and wet snow to move through. The snow potential is a little iffy because the temperature profile is borderline, but I’d say there’s a decent shot in the region to get some minor accumulations.
And the Friday-Monday stretch looks awfully busy as well. A couple more waves of low pressure will head in our direction, both of which also have tricky thermals that are on the edge of snow/ice/rain. The timing of these will get ironed out over the next few days…but there’s a pretty solid cold air damming signal on the models for late Saturday into Sunday that could produce snow/ice across the interior. We’ll have to keep a close eye on that one for the weekend warriors.
And looking farther out into early March…there is a massive -NAO brewing that has been signaled for some time now. The NAO is the North Atlantic Oscillation and is a measure of pressure over the north Atlantic. In layman’s terms, there will be a large area of high pressure building over Greenland and then eastern Canada. What does it mean for us? While the pattern isn’t overly cold for New England and nothing like early winter, a pattern like this will likely keep it from warming up in early March and will keep snow chances around. The strong blocking can also produce ‘cutoff’ storms in our neck of the woods down through the mid-Atlantic states.
Whether or not this produces a major winter storm for us, or just south of us, remains to be seen. But certainly these setups have produced in the past. An analog for the pattern is 1962, which featured a raging destructive nor’easter in the mid-Atlantic states. A little too strong of a -NAO can suppress storms south of us, so we’ll just have to wait and see if that’s the case this time around or if we’ll get a hit. Either way, the big warmth we have now likely won’t come back for at least a couple of weeks or longer. After all, it’s still winter!