It was about 1am this morning when the European model showed an all out blizzard for Connecticut. In that moment, I said to myself as an unapologetic snow lover: "This isn't locked in".
Today we here at SCW considered putting out a first call map but decided early on against it.
Another good call.
Since that early morning run, the "trend" for today has been virtually every piece of guidance sliding east, bringing less impacts to CT and far more uncertainty than we had hoped as forecasters with less than 72 hours before the storm arrives. Then, in the last few hours, some guidance has shifted west, indicating a bit of last minute model madness that reduces confidence in putting out snow predictions in the midst of a chaotic NWP period.
We are witnessing an unusually complex forecast, even though we have high confidence in the synoptic (large scale) pieces that will make this storm develop, explode, and track northeast. This is because the details, which usually don't come into focus until around this time, are extraordinarily sensitive to timing and amplitude changes impacting the overall outcome. Let's talk about it.
Below are the 18z EPS members. You will notice they are much more west and as a result, closer to the coast. Closer means higher impact, plain and simple.
This illustrates the above point perfectly. While synoptically (again large scale) we know a storm is coming and it will be big, the details on something like track diverges enough to introduce a lot of high end uncertainty on a potential high end event.
As we've been saying for days--even if this is a big storm, we have to beware of hype. By hype, we mean locking in monster solutions at a time frame that's too far away (i.e. now), and in a context where there is still high uncertainty on details (*cough* right now *cough*).
It's prudent to hold off on a snow map for now, but probably not much longer. We're going to wait to see what the overnight and early morning data says. That said, we can start talking impacts and probabilities for each of the scenarios TW laid out. That will help inform you and give you a sense of where we currently stand given the data...and using our own experience and analysis to forecast what happens next.
These are the same four from last night, with a deeper explanation and current percentage we think it'll come to pass.
Scenario 1 - Southern jet stream energy dives out of the midwest, through the Gulf of Mexico, into the Atlantic, leaving behind the northern shortwave (or northern jetstream if you will) leaving us with a relatively weak piece of energy to track from west to east over the state leaving us with a relatively weak snow event, while the southern energy slips well out to sea.
This scenario doesn't look viable. What we've seen in the guidance today is that there is a phase, but it's of varying degrees and timing/location. Nothing shows what would amount to a clipper, and none of the guidance seems to even hint at this possibility (as you can see above on the ensembles).
Percent Chance: Negligible (near zero)
Scenario 2 - Northern and southern stream energy do phase with each other, and they actually intensify rapidly creating a low pressure system that tracks well west of all current modeling bringing mainly mixed precip or rain to the state.
Much like TW said last night, no model is currently showing this scenario either. It's late in the game for such a dramatic shift, and nothing today has hinted at this being a viable possibility. Enough said.
Percent Chance: Negligible (near zero)
I really just wrote about 1 & 2 to close the loop. We won't be talking about them anymore unless we have to.
Scenario 3 - Northern and southern stream energy interact, phase and intensify, and track southeast of the "40/70 benchmark", moderate impact in western CT, and a high impact in eastern CT. Winter Storm Warning level snows for the entire state.
The trend today has been here, but the storm isn't today. Essentially, the models have preferred a less than perfect phase, which allows for the track to go a little further east.
That doesn't mean no storm. A storm is coming.
We're watching the northern stream, southern stream (and whether energy is held back) and confluence to the north in Canada. Each of which could help push things east. Right now, I don't think the further east GFS is going to verify verbatim. Even if the low is further east, we are going to see tremendous inflow and banding. This is important, because usually that means deformation (heavy snow) happens well west of the storm center. This is why folks even in western CT are likely to see at least a moderate snowfall.
If this scenario played out, after possible snow showers on Friday afternoon snow would break out early Saturday morning and last through the day with the heaviest during the afternoon and evening. It would be a moderate to high impact in western CT and high impact in eastern CT with moderate to heavy snowfall, gusty winds, difficult road conditions, and moderate coastal fooding. Snow would end late Saturday.
Percent Chance: 55%
Scenario 4 - Interaction, phasing, intensification. Track just inside 40/70, slightly north and west of benchmark. Major winter storm for entire state. Wind, snow, coastal flooding all big impacts.
This is the statewide big dog blockbuster scenario. Here, we'd probably be talking 12"+ totals across the state at least. This would be a well timed phase of the northern stream and southern stream, with the low vertically stacking after passing the benchmark and being captured, promoting a prolonged event.
If this scenario played out, after possible light snow on Friday afternoon snow would also break out early Saturday morning and last through the day with the heaviest during the afternoon and evening. Snow would likely end very early Sunday morning.
This would be a blizzard, even inland. We'd see high impacts across the board.
Some of the guidance late tonight is starting to show a more efficient phase and more favorable upper level evolution for a high end storm and west track, so while this is not the favored outcome right now, I think this scenario is gaining some ground, at least at the moment. The probabilities are 55/45 but there's not much daylight between the two in this forecaster's personal opinion.
Percent Chance: 45%
- There is high confidence that a major winter storm will develop and deliver moderate and/or major impacts to the state including snowfall, wind, and coastal flooding.
- The highest likelihood of major impacts is east of the CT River, with reduced confidence in western CT.
- There is high uncertainty on the specific track, which still needs to be resolved. That said, a moderate to major snowfall is expected statewide.
- Nobody should panic, but everyone should be prepared for a potentially high end winter weather event with the bulk of impacts on Saturday, and residual widespread travel problems on Sunday.
We will continue to provide updates as warranted. Expect a first call tomorrow.
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