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.
