jm1220

A good rule of thumb is wherever the 850 low tracks and SE of it won't stay snow for too long. In that area the mid levels are torching on southerly flow. The stronger the 850 low, the stronger the WAA. For days, models showed 20+ inches of snow for much of PA that storm despite a bad track for the mid level lows and a strong primary. I remember living in State College then and having 6" or so snow and then tons of sleet. There was light snow during the day, by dusk finally mod/heavy snow when the mix line started surging north, then the telltale massive aggregated flakes that mean warm air is partly melting the flakes aloft, then ping ping minutes later. Surface temps the whole time were in the teens. The backlash was good there because the coastal low finally took over, moisture was still around and cold mid level air came back. The end result was 11" or so of gunk that froze into cement.

I could see the larger system being a decent overrunning producer given the high ahead of it, but the high is pulling away and the flow is backing around to the SW too quickly, allowing a track too far west as of now and warm air to roar in aloft. Maybe the pattern out west could be a little more progressive and nudge it east, the trough could amp a little less, or the resistance in Canada could get a little tougher. But there's no help from the NAO, so nothing to force it to amplify less and surge warm air in with a track too far west. The SW flow aloft is also killer for a major snow event near where the low tracks and maybe even a good bit inland where there could be a zone of nasty icing and sleet. If there's a strong primary surging into OH or PA, I don't see much to force an early transfer to cut the warm air aloft off. You really want the trough to amplify less and track the low further southeast. There's still time for some adjustment there. But the initial overrunning should be good for a few inches hopefully.

The Friday small system in front of the larger one.

GFS surface temps are the absolute last place I’d go for any storm like this. It won’t be an intense system but should hopefully drop an inch or two areawide. The immediate coast and Midtown may be exceptions.

It's absolutely happened on the south shore. I remember a Dec 2005 storm that was 4-6" in northern Nassau and all rain in Long Beach. The 2/13/14 disaster was another one. It rained at my house for hours while north of Sunrise Highway raked it in.

Glad I live on the North Shore now!

Bottom line is we need a stop to the crazy Pacific Jet ASAP and a little (not too much) help from the NAO/AO to have an El Nino enhanced southern stream deliver the goods. It just takes one of these southern stream systems to obliterate us given the right setup, but have to get there first. This isn't a crazy Nino but 2002-03 wasn't either and that gave us PDII. 09-10 had some that delivered, some that didn't because of the same confluence, "Super Nino" Jan 2016 had the possibly best snowstorm in my backyard (that I missed ) in decades, the Feb 1983 blizzard, etc. I think if this winter amounts to much it'll be on a system (or two) like that timed right given what we've already seen so far in the storms that are targeting the Mid Atlantic.

I think that's something to watch. The bad luck part of this though might be the trough overamplifying and it hugging the coast, although looks like there would be a big high in the way to help overrunning. I think the pattern is finally switching up. This current storm would've been a beast with the few tweaks I mentioned. You can see how it already is in the Midwest, but too bad it's about to relatively shrivel up under the confluence sledgehammer.

The push down from the northern stream S/W looks to be greatest when the WAA is reaching our longitude, drying everything up and crushing the storm south. Nasty shortwave entering N NE and the Adirondacks to make that happen. Nothing but dry air roaring in on that setup. There'll be the usual northern wall of snow that makes it up to some latitude and stops and gets crushed east from there, but it seems dry air in general gets mixed into the storm and it can't really amplify and develop a massive WAA snow shield like it could with this southern stream trough because the confluence and northern stream press down is bad enough to deamplify everything. Like it'll go from flurries to a few inches over 50 miles instead of the flurries to well over a foot over 50 miles like 2/6/10 did. I'm sure parts of VA will walk away with a nice haul just like early Dec. A couple tweaks and it could've been much different just like that storm. Ridiculous.

Yuuuuuup. If it relaxed just a little it would be a major event probably even here. Horribly timed shortwave coming down from the northern stream and drying/crushing everything to crap just like the early Dec storm which also could've been a KU with a differently timed northern stream. Not sure if VA/NC specials are counted as KU storms.

All I know is, until the roaring Pacific Jet driven pattern ends, we can maybe sneak in a moderate snow event at best in between milder than normal conditions. The MJO being stuck isn’t good-we need it to move to a more favorable state. Will it turn around eventually-probably, but we’ll need to do some serious catching up to get everyone above or well above average snow. Maybe we can get a beast like the Jan 2016 storm but you can’t rely on something like that.

Looks like the progression of the MJO may finally be happening, which can finally put a trough back in the East and access to cold air when it gets to our favorable states. The 1-3/4 system can perhaps be interesting if there's a wave that can amplify enough and some cold air is left around. If the cold air is cut off by the roaring Pacific jet dominated airmass we've been having, it'll be hard for anything to happen regardless. We've had plenty of southern moisture but a totally uncooperative northern stream thus far-crushing/suppressing the major SE early Dec winter storm, and then retreating into Canada. We need the northern stream to help deliver the cold for any storm to deliver while the STJ provides the moisture. As for blocking-if there's a major -NAO episode, it may be to the benefit of the lower Mid Atlantic again and we get shafted like early Feb 2010 if we can't get some help getting a storm to turn the corner. So I wouldn't root on too strong of a blocking period. But it does look like a change is coming to the overall pattern in 7-10 days or so which at least puts us back in the game.

The sun angle gets worse every day from here on. Just sayin’

N NJ and E PA especially in elevated areas should have the heaviest totals by far given upslope on the deep moist SE flow and it being increasingly likely the firehose stays over NJ for most of the storm. 4-5” is a good possibility in some of those areas.

I'd watch the Poconos and NW NJ for flash flooding on Friday with the upcoming rain. Models are showing an upslope enhancement in those areas due to the very moist southerly flow reaching the hills/mountains and forced upward. That could be where you see 3-4" totals or locally more. Elsewhere, the heavy amounts will depend on how long the LLJ firehose stays overhead for the most part.