Isotherm.

Thanks for the welcome chiono. Below the 10hpa level, the ECMWF does have a split precursor appearance by the 15th. It could simply be a timing difference with the euro slower. But it is incontrovertible that the precursor pattern is strikingly w2, so I would expect the 10hpa level to acquire more of that appearance. It is possible euro / slower may be correct as MJO forcing likely won't peak until 15-18th on the vortex. GFS is correct on the w2 signature but it certainly isn't impossible that it is a little quick on the trigger. Either way, interesting stratosphere tracking ahead.

I have not been optimistic this winter from a CONUS standpoint insofar as the stratosphere, due in part to preset background conditions, and ongoing modulatory effects of mechanisms such as EEP via geomagnetic activity, robust westerly shear stress via the QBO, and poor tropical forcing. Additionally, up until the past couple of weeks, the brewer-Dobson circulation has been weaker than normal w/ concomitant decreased ozone transport. That has since improved dramatically. The alterations in late January via Aleutian stratospheric ridging and subsequent w1 forcing converging at the vortex has led to a technical SSW w/ much more susceptible vortex. It always appeared to me that reconsolidation would occur, but the question in my mind was the extent to which subsequent w2 assaults would impact the circulation. The upcoming period will feature enhanced w2 generation with a classic constructive interference regime across the northern hemisphere, in conjunction with propagating MJO wave signal. This will induce further Rossby wave driving applying more pressure to the vortex. As the U signal circulates the globe, we should see - initially - the low geopotential heights approach the W US Coast followed by retrogression, as well as the development of the first genuine -NAM/NAO of the winter. Some of the latest model data has been detecting the impacts of the w2 forcing on the vortex with the upwelling splitting activity throughout the stratosphere. If this occurs, my thinking is that the resultant tropospheric transformations would be fairly rapid due to present conditions, the nature and origin of this attack, and ongoing weak circulation further up in the atmosphere. Overall, it is difficult to ascertain low level impacts right now, but my confidence has been high on a AO/NAO reversal for mid February into March. Of course, we could revert to the base pattern; that's always a possibility, but I think the evidence is sufficiently strong to argue against such a notion at this juncture. By the way, I have been reading this board for awhile, and I think there are some very talented individuals posting here.