jm1220

I think it’s a little high as well but if higher ratios work out it’s possible. In any case the north bumps seem to have stopped so that’s good.

I agree. I remember the huge snow mounds in the city after the 3/14/17 storm even though a huge amount was sleet. Sleet has a disproportionately high impact for how much of it falls-1” of sleet is the same water content as 3-4” of snow and it tends to stick around a lot longer. I’d rather it snow all things considered but anyone who wants deep long lasting snowpack shouldn’t complain about some sleet thrown in after a big thump of snow.

This reminds me of the 12/17/20 storm overall-SWFE type system that transfers to a coastal system. 8” here from that one.

There’s like a 60 knot jet coming from the Gulf. There will definitely be a warm mid level layer and sleet in a wide area. It’s coming into a big high pressure area which causes the huge area of snow out ahead but it eventually becomes too much of a good thing. But sleet in the end is a plus if it freezes into the snow and turns it into concrete. This stuff won’t be going anywhere until we get a major torch.

If we get 2”/hour rates for 5 hours we know what that can add up to. This seems like the type of SWFE that can produce- heavy snow shield coming into a strong high pressure that provides an overrunning surface.

12/17/20 might be a pretty good one at the end. Hopefully the snow comes in better than that one did-I ended up with 8” but was hoping for 12+ but the snow shield broke up so the warm mid level air advanced faster.

Yep, seen it before too where if 750-800mb are wrecked by the initial primary lows hanging on too long it can take a while to flip back to snow. But the coastal storm evolution is the complex part of this that we have to wait and see on. It’s looking good for at least 4-6 hours or so of heavy snow before any warm mid level air arrives.

I think there’s an in house model group the NWS uses for this but someone with more information can add further.

We all know the tendency for these to trend north over time.

If we get 10” of snow with sleet mixed in at the end that will all freeze up and thicken the snowpack up, count that as a big win. Rather that than 15” all snow that melts faster.

We’re still not in a regime that allows for big coastal storms like before 2020. Still very progressive and favoring fast moving/suppressed or SWFE type systems. If this one trends to a SWFE type system although one that’s much larger and more far reaching than usual it would fit the mold.

It’s really not overly complicated, if we have a strong 700/850 low go NW of us, we will mix eventually-plain and simple. That means the winds at those levels are from the south and a warm direction. It doesn’t matter that the surface is cold. We could have a lot of snow fall before then but the same mechanism driving all the moisture from the Gulf also brings warm air. If the snow comes in like a wall it helps hold the warm mid level air back and we can pile it up quickly, if it comes in like shredded garbage it will disappoint and we get sleet sooner. We could also dry slot before or as that warm air arrives since dry air will pivot around the mid level lows from the south. We need the mid level confluence to force a further south transfer. If se see that retreating we have a typical SWFE setup. There’s the other possibility of a coastal system bringing snow back in but I think that won’t be determined until we’re closer in.

Definitely a positive with this storm that there seems to be a floor of at least a decent event with the initial overrunning surge and potential for something really great if we can get this coastal to crank in time.

Oh sure, if this stays intact it looks good for a few hours at least of couple inch per hour rates. That's a thumper if I ever saw it, and tons of moisture coming into the overrunning dome.

Yep I’ve seen it before where it’s been 10 degrees outside and we get tiny needle and sand flakes.

That would make sense, if we start out with good saturation and lift in the -12 to -18C cloud layer we get the best ratios from good snow growth. If that warms up we lose the best ratios. 20:1 is very rare even in the best setups and I’d argue we wouldn’t even want that as that would be pure fluff that would compact/blow away. I’m fine with less snow overall but longer lasting.

Look at 500mb before you look at the surface. What happens at 500mb drives what happens at the surface. You want to see strong confluence in SE Canada if we’re getting a full phase to our west. We’re having a ton of Gulf moisture overrunning into the high pressure dome so the surface is definitely relevant here, but the 500mb confluence allows that high to be in place and to force a redevelopment to our south. And you also want to pay attention to the 700/850mb low tracks, if they stay intact and track to our NW that means we have strong southerly flow from the Gulf at those levels and they will warm. But the big initial overrunning surge can mean a ton of snow falls before that warm air gets too potent at 750-800mb and whatever sleet just hardens up the snow pack into cement once it freezes up. I’ll gladly take 10 or 12” of mixed snow and sleet that freezes into cement.

Would have been 20” easy in Long Beach where I was then had we not wasted hours on heavy sleet. It absolutely dumped.

If this is turning into a SWFE those caveats apply. We need the snow to come in like a wall which hopefully we can make happen into a big high/overrunning surface like this, and it’s a race between the warm mid level air and how fast we can accumulate. The mid levels couldn’t care less about how cold the surface is. If we have 700/850 lows going NW of us and late transfer we will mix. But there could be a lot of snow before that happens. Plenty of time for trends in either direction and if the full phase happens we need the confluence or it will try to cut.

People need to stop using those maps and look at soundings to see if there are good chances for high ratios. If in doubt use 10-1. You want a saturated -12 to -18C layer and strong lift. Surface temps don’t determine ratios if you’re below freezing.

If we get 12”+ from heavy dumping snow on the front end and an hour of some sleet at the end I don’t think anybody would complain and if you do you need help. Like I said before our bigger 2020-21 storms mixed at the end.

Yikes. At the airport about to head home, currently 5 at the closest station to my house.

I’ll be perfectly fine with mixing for an hour at the end after a huge front ender thump. Other than the Super Bowl 2021 event all of our major events that winter mixed at some point. The 2/1/21 storm dumped 15-16” IMBY but a small part of it was sleet/rain.

If there’s less confluence and a full phase we could absolutely see an outcome like this where the primary goes well west of us. In that situation the usual caveats about SWFE apply: I-90 corridor is favored for all snow, here hopefully we get the heavy wall of snow before any warm air aloft comes in. But if you have closed mid level lows going west of you it will eventually happen.