The second half of "tornado season" - what will it bring?

Since the outbreak of May 4-6, it has been very quiet. The major polar vortex centers have shifted toward the Atlantic and Europe, leaving positive anomalies over the U.S. and a lackluster Pacific jet. This will likely change. I have been harping on renewed activity late this month, but that is most likely not happening on a grand scale. However a disturbance from the Pacific will dive into the CONUS and provide severe chances for the northern Plains for the next few days, with marginal moisture being the major limiting factor for an otherwise nice shortwave trough.

The bigger event should come in June. As the polar vortex centers shift back into the Pacific as Indian Ocean convection is renewed, the Pacific jet should be reasserted. The subtropical jet is still in full force and there has yet to be a full fledged subtropical block, meaning the jet will have a chance to extend into the eastern Pacific and amplify a trough. Obviously, this threat should be further north, most likely encompassing the Central and/or Northern Plains. And once again, just based on the trends this year, the Midwest should not get the brunt of severe. This idea is supported by the GFS ensembles, though the European model continues to show brutal ridging reasserting itself in early June.

As the month continues, the high should strengthen and I'd expect "summer" to truly set in around mid-June. Early June activity, IMO, will be the last gasp of Tornado Season 2007, which will go down in infamy as the biggest season in the Plains in 8 years, and comparable to the infamous seasons of 1995, 1993, and 1977. The reason for this is based on trends and the fact that the Pacific jet and Alaska vortex becomes a weaker factor closer to summer, compared to the building subtropical high.