Models are converging on idea of a southern branch storm gathering some moisture this upcoming Sunday and Monday and proceeding northeast toward the southern New England coastline. Though we are contending with a strengthening polar jet (as predicted) in this time frame, the longer range models have actually done a poor job at high latitudes. The SPC SREF projection for the probability of significant tornadoes is also startlingly high for the Monday evening event, as the graphic above shows. Based on the high helicity values, it looks like some of the most intense cells may be able to put down some strong tornadoes, but it will take another round of model guidance to confirm or reject this idea. And the icon for a slight chance of freezing drizzle is enough to send icicle-size shivers down any spine! More work is necessary in such icon research. A simple pair of gloves can make all the difference, but handbags, headbands, boots and more can really add to your personal style.

To make the composite analysis, years 1959, 1960, 1962, 1963, 1970, 1974, 1979, 1982, 1989, 1994, 1995, and 2000(1954, 1965, 1969, 1977, 1983, 1985, 1992, and 2001) are selected as years with positive(negative) AAO(DJF) anomalies. None indicate extreme cold but only the European is maintaining the positive PDO, intense Pacific jet stream. • Anyone in either of the moderate risk areas on Sunday or Monday should immediately prepare for potentially extreme weather, which may threaten lives and property. We see the highest probabilities placed in far northeastern Mississippi into northwest Alabama, located a bit east of the current Monday moderate risk area. It has allowed the recent slow advance of ice in the Hudson Bay and Northwest Passages to become a fast advance and in the case of the Hudson Bay, should allow for a complete freeze-over in the next few days. It does start with temperatures which should stay below the freezing mark beginning Sunday night and persisting through Sunday, December 22. That’s at least 7 days if you are keeping score at home. • Long-tracked, violent tornadoes may occur on either of those days.

A look at the Storm Prediction Center’s SREF (short range ensemble model guidance) projection for the probability of strong tornadoes only worsens this threat. Predicting tornadoes is a very difficult endeavor, but this graphic gives us an idea of where the worst tornado threat may be. A look at this image, showing maximum updraft helicity for the Sunday event, gives a clear indication of what we could be facing with this situation. Temperatures look just slightly above normal and the pattern should remain active with at least one storm to talk about Christmas week (Dec 23-27). Weather twitter has been discussing the GFS ensembles today at length. The snowfall outlook is starting to look more promising as well. Monday looks very nice as well. • A significant tornado event is expected Sunday and Monday. In the meantime, we have Saturday’s event to get through. This, like the last event has more than likely become another sunk cost in a sunk week of weather.

The example of Mount St. Helens underlines this, as first signals of a coming volcanic eruption could be noticed already three months before the actual eruption. The police are helpful and sympathetic. The National Weather Service is also very much aware they need to entrain social scientists into their communication efforts and are putting resources in this direction. I asked my colleagues in the NWS where these icons came and I was told one of the offices developed them, without the aid of any social scientists or objective evaluations of efficacy. The storm lacks that one dynamic polar kick and may thus pass as a flat wave but will nonetheless have some moisture and should result in a modest 5-10 inch much needed snowfall. Not much of a distinction there! There have been severe weather outbreaks, but this is an actual outbreak. Now the private sector does not have bragging rights about better weather icons. Weather icons are an attempt to quickly and intuitively communicate the type of weather expected, but as we will see, there are some issues.