Major update - Multiple threats coming at the turn of the month possible

OK yeah I wrote two days ago that I did not expect any major outbreaks in March. I will change that because the timing of the "big tamale" may be earlier than expected.

Note that the latest European has a significant system around the 240 hr range, and so did the 18Z GFS. I am divided on the threat will not materialize like what is depicted on those runs, because the fundamental pattern really is sorta tricky. Sure, we just had the reloading with the sleet storm over the NE, and that piece will reinforce the Hudson Bay PV, but the big problem is the flat ridge over the CONUS. When does this go away is the question? We've had the Aleutian blocking high now eroded. As the next system dives down into the CONUS, the energy over the EPAC will split, sending the next system into Mexico where it will cut off (still a severe threat around the 21st but not too big given that cutoffs usually don't produce a lot of severe). The other piece will deflect northward and form a very strong and deep polar vortex (PV) over Alaska. This is where it gets interesting.

As this happens, a massive block develops over Scandanavia (yes, another block, as I said blocks don't go away easily). Some ensemble members are progging closed 576 contours at 500mb over northern Scandanavia (keep in mind, this is March and that's near the Arctic circle!). So this pattern becomes pretty stagnant, with the PV on the Alaska and Russia side, and the block in northern Europe, and flat zonal flow pretty much everywhere except invof the block. So now the question is, how powerful does this block become? If it becomes so strong that there's cross polar flow, the PV over Alaska becomes essentially trapped. OTOH, if the block slowly breaks down, this will allow the PV energy to branch off. The timing of the PV branching off is indeed the timing of what I think could be an extremely active period. This, according to the GFS Ensemble mean, should occur ~228 hr.

However, as the PV branches off and leaves a small portion over the GOA to amplify into the next longwave over the western CONUS, what happens to the flat zonal ridge over the CONUS? This is why I am divided on the initial threat. If that ridge is too powerful, the low cuts off again. BUT, many of the biggest outbreaks occur after a cutoff over the SW is ejected out. The reason is that following pieces of energy start out more progressive and less amplified in the EPAC and thus don't have as much tendency to cut off after amplifying over the West (in fact, just take a look at Palm Sunday 1965 for an example of this, the pattern was very much in support of cutoffs, the the shortwave that spawned the outbreak just barely missed being cut off over the SW, even though the part that it split from did indeed cut off).

The next few disturbances after that are uncertain, but let me just say this: ANY disturbance which manages to stay progressive (the chances will be enhanced if we have semizonal Pacific jet with small kinks in it) will have the potential to be significant severe producers. This is going well after 240 hr, and will most likely feature big events from March 29-April 10. The caveat for multiple threats is if the first disturbance manages to really amplify and form into a new PV, which will shut down the pipeline.

Note that an alternative option would be for the big event to occur at ~240 hr, but although the mainstream models seem to show it, it seems like the less likely option right now.

All of this is subject to much change, of course, as this pattern's pretty dynamic and unpredictable.