CAPE

The complications in the evolution of this event are related to the highly amplified nature of the pattern- mostly the massive EPO ridge in conjunction with the NAO ridge. Some of this at the infancy stage has been discussed, but it is interesting to see the differences later in the process. There are 2 anticyclonic wave breaks that bridge the 2 ridges and influence the TPV that is 'squeezed' out underneath. Throw in the deep Aleutian trough and amplifying PNA ridge.. Notice the TPV being absorbed into the Aleutian trough, and the character of the PNA ridge as it bridges with the NAO ridge on the GEFS. The trough that is our storm is being influenced by the NAO ridge and the vortex underneath. Favorable for the desired outcome. Look at the EURO ens(CMC similar). PNA ridge bridge with the EPO, and the NW Canada TPV is interacting with the trough(the storm) downstream; the vortex/lower heights under the NAO ridge are largely absent, and the NAO ridge connects to the amped ridge ahead of the trough. Not what we want. The deep trough rotates back north as there is little resistance. Needless to say these are pretty significant differences at the time the storm is developing.

The way the coastal evolves on the 6z GEFS is literally as good as it gets in this set up.

Done whinging for a few hours now?

No idea if the GFS is more correct, but historically when we have this HL set up its depiction is what should happen. A classic (and useful) block looks like this.

6z GEFS lead wave

The GFS has been hinting at a weak wave on Christmas day for multiple runs. There is still a chance for a more significant storm on the 27th.

FSS take the whining to banter.

Like I said the other day, it will be interesting to see how this goes if we have a moderate Nino next winter. We usually see HL blocking and it has historically brought us more snow than avg in conjunction with an active STJ. If that combo can't work anymore then its time to move north I guess.

Some here didn't like that solution lol. Give me a consolidated big low even if it cuts.. front end thump!

The 6z GFS gave us a path to victory. The answer is a more significant vortex under the NAO ridge.

It's supposed to be a rare thing not to have a 50 50 low when their is a west based -nao....frustrating that this could be another spine runner Here is your puny '50-50' low squirting out into the NA as a ridge builds ahead of the deep upper low. This is how a "block" becomes ineffective.

It's not that simple. This is a big NS vort digging down, and there needs to be some resistance above it to inhibit it from rotating back northward(cutting). Without a vortex under the NAO ridge(a true block), the confluence/convergence is weak and upper heights just build there out in front as the shortwave digs. eta- anecdotal but a -NAO is probably most effective in a Nino with an active southern stream as primary waves are embedded in that, rather than emanating from the northern stream with a NW to SE angle of approach.

Incrementally weaker with the TPV under the block since 6z. Ultimately it ends up more like the Euro.

Through hour 75 GFS looks the same.

However long that video was, that's how much time out of your life you just wasted.

The model disparity in the handling of the TPV underscores the importance of having negative height anomalies underneath the NAO ridge in order for it to act as an effective block, encouraging a favorable storm track underneath. Fill that area in with a ridge and it becomes largely impotent and of little use to achieve the desired outcome.

NBM is useless given the disparity, and the blend probably includes models with low or no skill at this range. Only runs that matter are the next GFS and Euro.

Having a TPV under the block does more than just compress the flow. It spins off spokes of energy that can phase with and sharpen the primary wave in time for a coastal to get going south of our latitude. It actually encourages the wave to amplify/dig more, and take on a negative tilt.

The Euro was doing this a few days ago then trended away from it, but yeah I don't think we want the shortwave to be an entire TPV lobe lol.

Look at the 6z GFS run. I made a post on it earlier.

The runs with the better outcomes have lower heights there yes.

I think this is probably the best panel to see the differences. Continues the trend of ejecting less lead energy eastward underneath the NAO ridge.

In progress.

At this juncture the depiction on the means is reasonably close to what we want, but plenty of details that will determine the ultimate outcome remain unresolved.