Major Nor’Easter Likely Later Sunday

After our earliest 80 degree day on record we may be looking at an unusual (but not unheard of) spring snowstorm across Connecticut. There has been a fair amount of spread in our computer model solutions along with poor run-to-run continuity by some of our models. Today, there is fair agreement that a major nor’easter is likely.

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The European computer model is most impressive with near-blizzard conditions across Connecticut Sunday night and Monday morning. This would be a beast of a storm with over a foot of snow in many areas. There are other possibilities here, however.

The GFS model, our less than stellar American computer model, is stubbornly showing a weak and out-to-sea solution. This seems unlikely to me for a number of reasons including the fact most of the GFS ensemble member (21 versions of the GFS with slightly different tweaks and perturbations) are much more impressive than the operational GFS. Many members have a Euro-esque solution.

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I do think there is a reasonable chance the storm comes even farther west than the Euro shows which would introduce the chance for a wintry mix – particularly south and east of Hartford. The Euro Ensembles show a tight clustering between Block Island and Martha’s Vineyard which, if history is any guide, would introduce mixed precipitation in places.

You can see a hint of this on this map which shows the probability of seeing >6″ of snow. Basically what percentage of the 51 European Ensemble members show >6″ in any given area. There is a slight hint that inland areas – and especially the Berkshires – are favored. Regardless, probabilities greater than 70% over NW CT are quite impressive at this time range!

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It’s fair to say that a major nor’easter is the most likely outcome for Sunday night’s storm. The heaviest snow should fall Sunday evening and Sunday night – and there may be some issue with mixed precipitation. While there is a chance for a miss or a glancing blow I think those odds have gone down today.

 

Sunday Night Nor’Easter Threat Grows

Odds are increasing that we’ll be dealing with a significant nor’easter Sunday night and Monday morning. Last night’s European model shows a doozy of a snowstorm with a nor’easter taking a classic track for a Connecticut crushing.

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Note: this is also the new and improved European model which was just recently upgraded. The European ensembles (51 different European models each a bit perturbed or with slightly different model physics) have fairly high probabilities of >6″ of snow across Connecticut – around 50%!

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This storm is still not a lock. The GFS model is only a glancing blow (although a number of the GFS ensembles are big hits – at least 50% of them).

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There’s also a chance that the storm tracks too far west and winds up bringing a wintry mix of snow, sleet, and rain which would limit the amount of snow accumulation.

Putting it all together, the odds of a significant storm on Sunday night are increasing though there is still some uncertainty here. It is fair to say the goal posts are beginning to narrow a bit with signals growing for a pretty sizable system.

Weekend Nor’Easter – More Model Swings

Seeing our computer models swing back and forth from major snowstorm to out-to-sea miss never instills much confidence in any particular solution. As I’ve posted over the last few days the range of possible solutions Sunday night includes a miss, a glancing blow, or a major nor’easter – that hasn’t changed.

What is interesting is that the afternoon European model has shifted west by a significant margin showing a significant snowstorm for just about all of southern New England. This isn’t the only model now showing a major nor’easter and the potential for a major snowstorm.

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Is this a fluke? Maybe not. The European Ensembles (basically a low powered version of the European run 51 different times with various perturbations and changes to the model physics) are quite bullish. About 60% of the members show over 3″ of snow Sunday night across Connecticut!

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There’s no need to worry yet. We’re still between 4 and 5 days out and there are a number of plausible scenarios that wouldn’t result in significant snow. While a 96-108 hour forecast is low confidence to begin with this forecast is particularly low confidence due to the poor run-to-run consistency in our computer guidance.

Nor’Easter Update

There’s been a tick east overnight in our computer models which decreases the chance of getting a snowstorm in southern New England Sunday night and Monday. However, there’s still a large spread in possible solutions ranging from a major snowstorm to complete miss to the east though the odds of a miss or only minor event are certainly higher than a significant storm.

Here’s the overnight European forecast showing a glancing blow with a minor amount of snow over Connecticut.

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The GFS is equally unimpressive – with a majority of GFS ensemble members showing a miss. There are, however, a few bullish GFS ensemble members that deliver a significant snow to the region. You can see that on this plume diagram with one member showing 0.3″ of liquid and two members showing around 0.75″ liquid (you can think of this as 3″ and 7″ of snow, respectively as a very rough approximation).

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There is still a big caution flag here. The overnight European Ensembles remain more bullish than either the GFS or European. The 51-member Euro Ensembles (designed to give a range of possible solutions) has a number of very bullish members and the mean solution is much more farther west than the operational Euro. There has been a shift east here as well overnight.

Potentially Wild Week of Weather

March can be fun for meteorologists in Connecticut. There are two main things that I’m watching – the potential for gusty winds, small hail and thunderstorms on Thursday and a nearby nor’easter Sunday night and Monday.

Let’s start with the nor’easter. There is a fair amount of spread in current model solutions ranging from a major snowstorm to a whiff to the east (GFS). In between is the European model solution.

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While the GFS and to a lesser extent the Euro are tame solutions there are signs that we need to watch this very closely. First of all, the Euro Ensemble mean is tucked inside and west of the operational Euro. This tends to be a big caution flag.

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While there are some out to sea solutions among the 51 ensemble members there is a rather notable clustering (in fact the tightest clustering) over the “benchmark” of 40N/70W which is significant. Does this make sense? It’s actually a decent pattern for a snowstorm with downstream ridging over Greenland and some semblance of a 50/50 low – that upper level low near Newfoundland.

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So…. we watch. Cold air and a favorable pattern for a storm are big signs to watch this closely. I think it’s fair to say there’s about a 50/50 shot at a decent nor’easter in Connecticut. Whether it’s rain, snow or both it’s just too early to say – but if the storm track is right this could be a significant winter storm in southern New England.

Now, backing up to Thursday. A pool of very cold temperatures in the mid levels of the atmosphere will lead to an impressive unstable airmass overhead. In fact, 500mb temperatures of -33C will lead to exceptionally steep lapse rates. What do I mean by that? There’s going to be an unusually large difference between temperatures between the ground and temperatures 20,000 feet up.

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What does this mean for sensible weather? Gusty winds – possibly up to 50 mph are a decent bet. In addition, IF we can muster up adequate moisture thunderstorms could produce small hail and damaging wind gusts. This is a possibility. Soundings from both the NAM and GFS show classic inverted-V profiles which is a classic sign for strong winds if thunderstorms can develop.

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