Webberweather53
Meteorologist
While uncertainty remains wrt whether we see suppression or an amped storm with snow and ice focused moreso in the OHV, interior NE, & mid-Atlantic and fringe snow/ice in CAD favored areas of the Carolinas and perhaps far NE GA, there’s an inherent risk for more amped storms further north in a pattern like this where we have North Atlantic blocking (-NAO) coupled to an strong Aleutian Low (+NPO/+EPO).
When you actually boil down to why this may be true, a lot of this has to do with how the mean flow alters the PDF of phase speeds of waves in the northern and southern branches of the mid latitude jet. Conservation of angular momentum and increased baroclinicity dictate that the background flow that steers northern stream waves is faster while shortwaves within the subtropical jet are on average considerably slower. When you get a pattern with North Atlantic blocking and a stronger Aleutian low, cyclonic wave breaking over the E US and phasing between these two streams is favored because the -NAO decelerates the northern stream waves upstream whereas the strong Aleutian Low/Pacific jet increases the speeds of southern branch systems, making said phases speeds between the waves more comparable and phasing which leads to increased wave amplification more likely thus making stronger coastal lows more likely. A pattern we’ve seen predominate the last several years with North Pacific blocking, SE Canada vortex, and +NAO increases the geopotential height gradient across the breadth of the northern branch of the jet and accelerates the northern stream waves while North Pacific Rex blocking can decelerate the southern subtropical disturbances even more, in addition to increasing confluence over the E US that shears and desmplifies the southern stream wave.
All of the above provides reasoning why timing of the waves may be even more critical in regimes like this with North Atantic blocking and strong Aleutian low and can somewhat explain the variability in storm intensity, type, and preferred regions for cold/snow in specific EPO and NAO base states.
Just some food for thought.
When you actually boil down to why this may be true, a lot of this has to do with how the mean flow alters the PDF of phase speeds of waves in the northern and southern branches of the mid latitude jet. Conservation of angular momentum and increased baroclinicity dictate that the background flow that steers northern stream waves is faster while shortwaves within the subtropical jet are on average considerably slower. When you get a pattern with North Atlantic blocking and a stronger Aleutian low, cyclonic wave breaking over the E US and phasing between these two streams is favored because the -NAO decelerates the northern stream waves upstream whereas the strong Aleutian Low/Pacific jet increases the speeds of southern branch systems, making said phases speeds between the waves more comparable and phasing which leads to increased wave amplification more likely thus making stronger coastal lows more likely. A pattern we’ve seen predominate the last several years with North Pacific blocking, SE Canada vortex, and +NAO increases the geopotential height gradient across the breadth of the northern branch of the jet and accelerates the northern stream waves while North Pacific Rex blocking can decelerate the southern subtropical disturbances even more, in addition to increasing confluence over the E US that shears and desmplifies the southern stream wave.
All of the above provides reasoning why timing of the waves may be even more critical in regimes like this with North Atantic blocking and strong Aleutian low and can somewhat explain the variability in storm intensity, type, and preferred regions for cold/snow in specific EPO and NAO base states.
Just some food for thought.
