weatherwiz

I am going to LOVE tracking this one in real time. At this point we can put the models away, put the QPF maps away, and stop beating "QPF trends" with a hammer. None of that really matters because it's all about how the banding is going to evolve, where the banding traverses, and whether we see multiple or even several bands. So it all comes down to the evolution of the mid-level with respect to frontogenesis and the 700mb warm front. This one is going to have major surprises and there is no way to pin those down, even at this time frame. You may see a scenario where you have a narrow swath of 6-7" and you go 10-15 miles on either side of this swath and totals are only 2-3". There is just no way to portray this on a map so the best you can probably do is a larger range and understand there is an equal chance of ending up on the lower range (perhaps even an inch or two below) as there is of ending up towards the higher range. With this I don't think I'll make any changes to my map from yesterday (don't even have time anyways). If anything I would probably adjust the boundaries of the totals maybe but I can't see adding in like an area of 6-9 or 6-10". Not sure how widespread that will be and that is going to happen where the best banding is. Other than this I think its definitely a good 4-7" for everyone but there will be reports as low as 3-4".

Lower Hudson Valley into Fairfield County I think may end up in the sweet spot. I was really thinking there was room for some of the heavier banding to end up pretty far north like the NAM has. Even though the NAM is kind of alone there are two things the NAM are great at sniffing out, warm layers and banding. But the NAM has seemed to back off on the intense fronto band it had on some earlier runs but also argues for multiple bands. But one thing that is going to enhance things in the Lower HV into Fairfield County will be the proximity to the mix line and 700 warm front. It will really dump here. If anyone is going to end up with something along the lines of 8-10" it will be within this area. I am wondering if the sharp cutoff line will end up from like just west of Springfield to around Hartford south to like Guilford.

I will be shocked if there aren't thundersnow reports in the Lower Hudson Valley/Fairfield County tonight

Electric Blue could get 7" and Kevin only 3"

I wanted to add a 2-4" area out that way on my map yesterday but kind of held off because of the uncertainty but it's an interesting signal and models can really struggle with that.

That is correct. When you see that signature that indicates strong upward vertical motion which will transport moisture into the DGZ and that's when you're most likely to get dendrites which accumulate efficiently. There are some other factors which need to be considered as well though. But here is an example from coolwx.com of the 6z NAM for BDL. This site is pretty cool if you don't have bufkit but you can see the maximum omega bisecting the DGZ Say you wanted to look for it on forecast soundings. What you would do is fine the DGZ (which is usually a colored as a yellow area on the temperature line) then on the left look at the omega (horizontal purple lines which indicate upward motion). The longer the lines, the stronger the lift and you want longer lines to match up to where the DGZ is.

ehhh some people put faith in the Cowboys every year

You would get into the heavy stuff too on the 3km. The 3km definitely isn't bad looking. Its a wall of snow coming in but it quickly starts to lose its oomph as it moves east.

the NAM really diminishes that fronto quickly. It's like a 2-3 hour period (if even 3 hours) of very heavy snow and done. Western CT/MA could get 6-7" and EOR could get like 2-3" lol. That cutoff is going to be pretty wild. Might have to re-think about the Fairfield County jack...that's probably best area to get thundersnow and rates closer to 3" per hour

Under the banding the snowfall rates would probably approach 2"/hr and maybe even upwards of 2.5". Feasibly, because of the crosshair signature (the -30 dissecting the snow growth zone) that should elicit great snowgrowth...the dendrites which accumulate quickly. I am a little worried though we may not get the perfect dendrites and snow growth will be a bit impacted by some dry air. The big question is what happens outside of the banding...that's where there could be more of a struggle and if we end up with multiple band signatures there will be some screw zones. In between these, perhaps even outside the banding, this is where you'll get more in the way of Arctic dust. Regardless, a widespread 4-7" is still in the cards but we need to be mindful there will be some screw zones. I don't think we'll see many totals eclipse 7-8" only because its really a 3 hour period of heavy accumulating snow and that's it. This is going to be fun to track in real time

6z NAM bufkit for BDL. When I see -30 into the DGZ I get all tingly

Have I had too much egg nogg or are there double posts?

The ones that are still likely sleet for NYC?

There’s going to be a warm layer aloft but it probably won’t be significant for anyone in SNE but there’s a very real possibility NYC gets brief snow then goes to sleet. what the warm layer aloft will mean to us is where that warm front ends up residing and how strong exactly is it. Northeast of this is where the banding, snowfall rates, and ratios will be enhanced.

Ughhh sucks cod soundings still aren’t working for mobile

500/750 RH has me a bit nervous as to how robust the band may truly be. I’m still a little worried the overall axis is going to be quite narrow

That’s my thinking as well. It doesn’t look as impressive with the fronto and I’m taking that as the best banding will be more southwest of previous runs

I need 4.5” to hit 10” as well which would leave me with needing 90” to hit 100

One factor to also consider for the swath of max totals is how wide is the band in reality. May end up a bit more narrow than what’s being shown via max QPF swath.

Once the storm passes

We have very similar thoughts on this. But you’ve been consistent since multiple days ago…took me a few days to catch on

Updated map and even a blog post https://weatherwiz.blogspot.com/2025/12/friday-december-26-2025-southern-new.html

It's very possible. If there is any setup that the NAM is going to outperform other guidance it is going to be this. The globals aren't particularly skillful when it comes to banding. In terms of other mesos, I don't even think the HRRR handles that well. The best thing I think to do is forget QPF amounts and QPF trends and using those to define the storm trends. The focus and assessment should be on the mid-levels and particularly that mid-level warm front. Often, models will produce the heaviest QPF right under directly under where the best dynamics or fronto or gradient is but more time than not the heaviest QPF is going to be displaced a bit north of this.

If you look at where models (NAM, GFS, Euro) have the 700mb warm front...the NAM actually I think makes sense with how far north and east it has the banding. I think the area of strongest frontogenesis on the 12z RGEM would be northeast of where it has it

do you know how well historically the RGEM handles banding?