Composite of two of Andrews blog posts of April 4 and April 5
"... Current state of the atmosphere is rather bizarre in my opinion, with the United States (henceforth abbreviated as CONUS) under a deep closed low centered in the Plains at this hour. This closed low attains a minimum pressure of over 1000 millibars, although that value is deceiving. Observed temperatures show 60 and 70-degree temperatures being thrown up across the Southeast and Ohio Valley on the eastern side of this storm system as it meanders in the Plains. Further to the north, massive high pressure acts as a barrier to protect Canada from this closed low and bring a stretch of rather quiet weather to the region. Greenland is under a solid storm system, indicating that the North Atlantic Oscillation (NAO) is in its positive (warm weather for the CONUS) phase. A lack of defined height anomalies across the Arctic doesn't help me as far as trying to figure out synoptic temperature trends over the next 48-72 hours. Dynamic situation set up in East Asia, as a strong storm system is going to battle with two ridges of high pressure. Bering Sea is void of any significant height anomalies, complicating the act of figuring out just what the atmosphere wants to do in the aspect of warm or cold temperature trends in coming days...."
"It looks like an Arctic Outbreak may be in the offing for the middle days of May, just as many began to think that the chilly spring would finally retreat......Minimum temperatures for the morning of May 14th tell the story, with widespread temperatures in the 20s and 30s extending across Canada and well into the Plains, Great Lakes and Midwest. We even see the freezing line pushing towards northern Missouri and southern Nebraska. As I told above, model guidance is uncertain on the evolution of this scenario. American model guidance is unsupportive, and European guidance that is supportive of such an incident happening is rather inconsistent from run to run. I prefer to leave this event at the 'possible' level rather than elaborating on how this could all go down- I really want to see more model support for this situation before going ahead with potential implications and other effects of this arctic outbreak....
... Examination of the long range brings us to the morning of May 18th, using the same ensemble set and same 500mb height anomaly index. General atmospheric flow is much more zonal across the board in the long range, with high pressure dominating the United States and western Canada. Such a zonal flow would certainly allow for at least seasonable temperatures to develop across the nation. I am skeptical of low pressure trying to push south through Canada; I fear that the ensembles are overdoing the zonal flow in the CONUS, and cooler weather may be in store for the Upper Midwest in the long range. Arctic Oscillation remains positive in the long range, and North Atlantic Oscillation follows suit. As we get closer to this date of May 18th, I expect the ensembles to see this highly zonal flow turn more meridional- ensemble sets have a natural tendency to make the atmospheric flow far too calm than what ends up happening."