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2 Systems To Watch This Weekend

Oh, I had forgotten how lovely it feels to have your nostrils freeze. Today brings the coldest air since early March, back in the depths of our epic winter of 2015. But those who aren't fans of popsicle nose-hairs need not fear - this isn't sticking around. The core of this quick arctic shot is already on the way out, and after a cold night tonight we'll be warming right back up above average for the rest of the week. Wednesday and Thursday bring bright skies and high temps mainly in the 40s. Easy stuff to take for January. Friday and Saturday we're still around 40, although things do get more interesting this weekend. And that's where we'll focus for this post.

setup1

First up, a system approaching for Saturday. This one doesn't look terribly potent, but enough to cause some issues. There should be just enough cold air around, particularly in the interior of SNE/points farther north, to go through a period of wintry mix. That means a good chance of snow/sleet/ice and perhaps even a changeover to some rain. While not a major storm, this is similar to the type of event we had in the final week of December. Just pesky enough to cause problems. Right now it does not appear there will be enough cold air near the coast/southeast Mass to have much in the way of significant wintry weather and there's no need to go canceling plans at this point. We'll monitor the trends as we get closer and have updates on the finer details of what this will eventually bring.

splitflow

Easy to spot the split-flow across North America late this week, with the polar jet stream zipping across southern Canada and the strong subtropical jet stream blasting across the southern tier of the country. These setups rarely offer much confidence more than 3-5 days out. Source: Weatherbell

After a brief break, another piece of energy will spin its way toward the Northeast. Model guidance has been all over the place with this one, having a tough time reconciling multiple disturbances in the mid/upper levels and a split flow between the polar and subtropical jet streams. It's a notoriously tough setup to forecast much in advance, which is why there hasn't been a lot of clarity yet.

What we know is that there will be limited cold air here in New England, and so we would require either A) a dynamic system that can produce some of its own cold air and/or B) a perfect track near the benchmark (40N 70W) to really bring a significant winter storm. Sitting 5-6 days out, I'd say chances for any snow certainly favor the interior, outside of I-495 - and that's IF the storm develops. Some guidance keeps it far enough out to sea to keep us high and dry.

lows

Monday's 12z ECMWF ensemble members, showing guidance for Sunday night. There's a very wide spread in outcomes still, and that's expected to stay the case for at least another couple of days. Source: Weatherbell

Ensemble members of the ECMWF show this uncertainty well. Note that amongst all the members there is a wide spread, which in turn means low confidence. The operational runs and ensemble mean have mainly shown an inside runner, which would produce more rain than anything else here in the Boston area. Many times we see tracks like this 5-6 days out, but the trend moves farther east over time. So that's something we'll have to be wary of over these next few days.

Also worth noting that many of the lows are very potent. The pattern says that a strong storm system is definitely possible, which gets our attention. Bottom line is that it's a forecast that requires fine-tuning, and with full disclosure I doubt we'll really have a great handle on it until much later this week when all the players are getting closer.

 

latejan

Latest ECMWF weeklies showing a return to milder times in the Northeast to end January, with a stormy west. Lots of Pacific air would enter the country in this kind of pattern, which is much more temperate than arctic air. Source: Weatherbell

So what's in store farther down the road? Pretty typical El Nino conditions. Transient cold shots and a storm outlook that's completely contingent on timing. While the air behind the Sunday-Monday storm will be quite cold, it won't stick around for long. Indications are for milder air to move back in after a few days, with an overall milder than average end to January. But it should also feature an active subtropical jet stream and several opportunities for storms. I've said it before but it bears repeating - you don't need below average temps for a winter storm around here. It's the coldest time of the year for starters, and the outcome of these storms will simply come down to whether or not the timing is right. One well-timed cold shot, linking up with an active STJ, can still deliver. So snow lovers shouldn't get that worried just yet. What we're seeing is pretty typical of a strong El Nino and in line with the winter outlook up to this point.

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