psuhoffman

I wanted to post this earlier this morning but didn't have the time so then I figured I would wait until after the 12z models came in. But I wanted to explain why, as many have pointed out by now, the "favorable" changes earlier in runs don't seem to have much impact on the final end result. They have had some incremental benefits...which can result in an extra inch or two and maybe less of a warm up during the storm...but a rather significant 100 mile better track of the SW or the SLP early on at hour 60 or 72 ends up having very minimal impact later. It has to do with what happens around hour 78 or 18z Sunday. The changes we are seeing with the track of the SW and the SLP and the minor changes in the height field early on have little impact because they don't affect what happens Sunday much. First of all this was the look on that one GFS run that smoked us with a flush clean hit a few days ago. Notice the trough alignment is still slightly positive, and most importantly the flow over the top is pretty flat. There is just enough ridging to allow it to gain some latitude but its clearly going to move NE or ENE and not north or NNE. Now look at the latest run... The trough is very negative and the flow over the top is going to allow this to lift north. The H5 low is pretty similar here...what changed the most was 2 things. Look up near Greenland...we had a legit NAO block for a few runs that eroded into just a NAO ridge and ended up even more east based then progged. The result is the "blocked" flow ends up significantly further north and the orientation is all wrong. This allows the next NS wave to amplify southward and sharpen the trough which pumps the ridging over the top even more. This is the SLP position and H85 winds at 18z Sunday. There is nothing wrong with this low position. But the problem is because the Upper low is fully mature and amplified already at this point...even though the coastal is in its formative stages it already has an extremely powerful SE flow ahead of it. Actually because the surface low isn't yet well developed...its allowing the SE flow from the mature mid and upper level lows to dominate and drive well inland ahead of the low. This is going to blast the baroclinic zone well inland and create a natural boundary for the surface low to track. Add in the convection and the pressure falls that will induce and the low is going to chase that boundary due north from here, maybe even NNW. Here's the rub...it doesn't much matter exactly how the H5 or surface low tracks before this (to a point, coming back to that later)...because at this point the storm is about to phase and its happening at the worst possible time. As this happens the energy diving in behind (that was coming over the top a few days ago) is going to tug on this and pull it in. The further southeast it starts...it simply pulls it even further NW because the end point of the phase will be in middle between the two pieces of energy. They want to "come together". So if it starts further southeast....so long as that phase happens at that time...its just going to pull it further NW to make the phase happen. The changes will be there but much less then you would think from earlier trends. Looking at the exact SLP track on Saturday has little to do with this process (to a point). Minor changes in the height field over new england on Friday or Saturday have little impact because with the changes to the blocking, and that is not going to change back at this point, the trough up there will be long gone and not helpful at all by Sunday when this is happening. Its totally irrelevant what the heights are on Saturday by Sunday. The timing of this system and how it tracks rendered that moot. When it was 24 hours faster and coming in further north the spacing there mattered. Its no longer a factor at all imo. Now I said these things don't matter...too a point. They are nudging this on the margins...and if we were to get a continuous shift eventually we could get enough of a track adjustment to help some. But what matters more than some adjustment of the SLP or H5 early on is when and how the phase happens and how strong the mid and upper level features are over the southeast. We want a weaker trend more so than a location trend on the H5 low imo. Less wound up will induce less of a SE flow and the eventual phase and pull NW of the surface track could be less extreme or delayed. If we can get the surface low off to Hatteras before the capture and turn north we will do well. Thats only a delay of like 3-6 hours. That would be the best case scenario. But again I think the amplitude of the system has more to do with that than the exact track. Don't get me wrong further SE is good...but it has "limited" impact later...vs a weaker trend in the H5 would have a more dramatic difference imo. The other option would be an earlier phase...which would dry slot the crap out of us but would at least avoid the lower levels torching. After the phase the surface low once it tucks and stacks will turn back northeast...if that process were to happen further south the track could still stay east of us...but again the storm would be a mess with a huge dry slot as it passed us. Our problem is the phase and tuck/stack process is happening at the exact worst spot for us. Delay that by a few hours and get this to track up or east of the bay instead of up west of it and we would have a significantly better outcome.

I’d be very surprised if we didn’t get some snow. It’s not a lock yet but maybe a 90% probability of at least 1” imo. What we’re figuring out now is it some snow washed away by rain or a storm where we have a nice snowpack when it’s over.

You took your meds today

Not necessarily…the low gets into southeast VA. At that time it’s snowing here. Cold airmass in place will take several hours to erode even with the SE flow. From there yea the low moves N instead of NE and eventually that warms us but until it gets up into central VA were probably ok. And once it gets to us we probably dry slot. Getting it to our south before it turns north is huge here.

I don’t thunk 18z eps was west. It just was deeper due to a few more amped members and less outliers. So there was the illusion of a west shift by adding some more isobars and colors within the broader low position of 12z. The axis of the snow probabilities and means didn’t change at all and looking at the individual low plots they’re clustered about the same as 12z. Additionally there are more misses to the southeast, at least for the northwestern part of this sub, then I expected.

I’m probably making it sound worse than it is. The 18z euro control (and it looked very similar at 90 to the op euro so I think it’s safe to say this is about what the 18z euro was just lower resolution) was fine. Just saying given what it looked like at 90-100 hours a but shocking the low ends up over Hagerstown. But this seems acceptable Imo. We can thank the cold airmass in place for these results despite the track.

18z euro control does the same thing the Gfs does. Cuts the low from Wilmington NC to Hagerstown MD. Lol. It has the same improved look at 90 as the op but it seems the more amplified SW offsets those other improvements. The storm gets to eastern NC then goes nuts. By then the confluence is gone and nothing but ridging over the top so nothing to stop it from cutting due north.

The time on the link is wrong it’s from the last zoom. I’ll open tonight at 10:20. Quick discussion of the early high resolution runs then icon and Gfs. Can’t stay up for euro unfortunately.

Same link as before. Email me at [email protected] if you need the link.

I’ll open the zoom around 10:20 and stay until at least 11.

Email me at [email protected] and I’ll forward you the link. This goes for anyone else that needs it. Same link as last time.

Any interest in a short zoom tonight as Gfs comes in?

I could do a shorter one as 0z Gfs rolls in tonight if people want.

We better switch to geico…

Last comp. It’s hard to compare because the Gfs is much faster but if you take the Gfs when it had the h5 and surface low where the euro does at 90 hrs the euro is significant colder and south. Which is pretty amazing given the Gfs was at that point 12 hours sooner with less time to scour the fresh cold airmass.

One last positive and something I keep coming back too. It’s COLD in front. This has the best antecedent airmass of all the analogs we’re throwing around. That might make a big difference.

Where 18z EC it ends at 90 it’s hard to say. You would think it looks great just from this… The positives…the surface low is SE of 12z at 90 hrs. So is the h5 low. Slightly more confluence and suppressive flow over the northeast. Negatives… the h5 is more amplified, there is slightly more ridging to the north of the low and as the tpv lobe exits to our north that’s a problem. Unknowns…how the phasing is going to occur Overall I think this is a slight improvement over 12z. This is going to turn north but getting it faster and further southeast before that happens is our best bet Imo.

The differences I described above continue through 78 hours.

Through 66 it is (good). SW slightly east of 12z and less ridging and lower heights in front of it. High is slightly south. Slight improvements from what I can see. Obviously though we don’t know about the most important part which is the phase that happens later.

Of course he does it’s State Colleges biggest snowstorm ever. Lol. But it is a good analog but so is an early Jan 94 storm and Jan 12 96 and Feb 14 and there was a storm in December 2012 somewhat similar and they all had slightly different end results. He chooses the one that gave him 28” of course lol.

The ensembles look closer to what I think the op should have looked like post 96 hours lol.

Guys remember the old 5 day business planner in the 90s sponsored by Juan Valdez and Days Inn? Today the storm would have been on the very last day of that forecast. How seriously did anyone take the day 5 of that thing? Would we have dreamed of discussing the meso scale details we are right now? Yes maybe this should temper our enthusiasm some but my real point is to be amazed and how far we’ve come!

To be fair over the last 36 hours all the solutions among the more reliable globals have been between a coastal hugger and an inside runner. They all track the low somewhere through central or eastern NC and at our latitude between the Delmarva and Dulles. For 120 hours away that’s remarkably narrow goalposts imo. It’s just that we’re on a razors edge between a significant snowstorm or something less impactful. But 30 years ago we likely would be looking at goalposts between Indiana and Bermuda for the track at 5 days out! We’re now talking about details at day 5 we couldn’t imagine at day 2 when I first got into this game.

History of similar synoptic situations says something like this is more likely