Update; multiple threats at end of month and perhaps early April

The severe threat for this week does not seem significant to me, cutoff lows usually do not do much in the way of severe. I do not think there is any major event regarding the cutoff.

A lot of things look up for major events (perhaps four), coming up in the next two-three weeks. First of all is the one that I sorta called off twice. Way back about 1-2 weeks ago, I had predicted an event around this time period (did not write it on the blog). Then I "cancelled" the event after models had consistently predicted no such event would happen for several days. Shortly after that, the models caught on (goes to show that it's perhaps better to go with observations and extrapolation than pure models in the long range). But I had doubts on whether it would cut off, and believing that it would, in my last post I had written that it might.

That idea looks to be wrong. A strong Pacific jet will prevent that from happening this time. The 500mb hemispheric pattern looks pretty ideal, in fact. In many outbreaks, there was a cutoff or a closed low over the SW that gave way to a strong jet stream which drove a larger, more mobile longwave trough that ended up being a big event. The reloading period had already been done a few days ago. Right now, the key continues to be the ridging over the CONUS.

Revision: the posts I had...
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1831884
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1832127
http://www.easternuswx.com/bb/index.php?s=&showtopic=128581&view=findpost&p=1833459

There are two disturbances that the renouned polar vortex over Alaska (key forsynoptic severe outbreaks) are going to spit out. One initially will amplify pretty far west according to models. The problem with this one is because it amplifys over the EPAC instead of the Intermountain West, it will likely become very high amplitude once it approaches the Plains, and thus, shear vectors will be unidirectional. Another potential problem is regarding moisture return, since models do predict a closed low over the Bermuda area which could lead to a high pressure cell too far north to tap into a Caribbean moisture source. Although I believe the models are underdoing the moisture return, most of the biggest outbreaks do not have that feature and instead have a semizonal, maybe slightly purturbed, flow.

The second disturbance is the question mark. If this trough materializes, it has a lot of potential. This one should have a source region closer to Alaska as the polar vortex splits, and one piece flies into Siberia. The question mark for this is indeed how the first trough moves away, and how strong a ridge is left behind over the southern CONUS. Will it amplify? If the first trough does not move away quickly enough, will there be enough return flow and instability? All those questions should be resolved within the coming days. FWIW, the Euro has been questioning the validity of the possibility of this, being incredibly pessimistic. So obviously, I'd trust the better model for now. Analysis, extrapolation, and pattern recognition suggests that in a case like this, the more widespread severe wx the first produces, the less the second produces. So really, I don't know which is bigger, except that I'd expect a least one significant severe wx outbreak with these two threats.

As the other piece of the PV moves into Siberia, the pattern will reload. A ridge will redevelop over the Aleutians, but it will be short-lived as the reformed polar vortex over Siberia reinvigorates the Pacific jet, which will most likely undercut the Aleutians ridge yet again. This new piece could lead to another big event in early April.

Stay tuned.