BOSTON (CBS) – We have had perfect Christmas snow on the ground for a week. It was festive and set the mood, but snow is always rented and doesn’t belong. It’s supposed to get back into the atmosphere by Christmas morning. Instead of a white Christmas, this one will be in the 2020 style that you can imagine. A soaked, windy, warm meltdown.
The biggest headline for this extremely unusual storm system is the wind being propelled by one of the more powerful, low-level jet streams you will ever see at this time of year. This is a “river of the wind,” only a few thousand feet high that will roar at 75-85 knots on Christmas morning. Not everything will make it to us on site, but widespread gusts of 40 to 65 mph from the south are expected, with some isolated gusts of 65 to 75 mph over high terrain (like Blue Hill) possible.
The strongest winds blow between around 7 a.m. and 12 noon on Christmas Day, accompanied by very heavy rains. It would be a good idea to prepare for a Christmas Day without electricity because thousands of people are sure to lose it for a while. Turn on the electronics, have the batteries ready, and it may be a good idea to take off some Christmas decorations (inflatables, etc.) before going to bed outdoors. Also a good idea, if possible, to avoid parking under trees.
This wind will deliver an almost record-breaking warm mass of air straight from the tropics, with Santa Claus wearing shorts. We’ll move up into the 50s on Thursday (Christmas Eve) and see these readings rise overnight. By the time we start tearing up presents under the tree, some low 60s could invade. This will threaten some all-time highs in the region that were just set in 2015.
For the ride comes exceptionally humid air with dew points close to 60F. Winter dew points near 60F have occurred only a few times in the past 140+ years, so this is rare air. Dew points like these are also the most efficient way to chew up the snowpack, as they help break the icy molecular bonds and quickly chew the snowy landscape apart. We expect almost complete loss of snow cover in southern New England by late Christmas morning.
The runoff from this melting snow is added to 1 to 3 inches of rain, the most stable Christmas morning by early afternoon. Lots of bad drainage flooding is likely and you should keep an eye on basements. Sump pumps will be busy! The rain and snowmelt effectively make this a 3-4 inch rainstorm. Rapid climbs on smaller rivers and streams are likely. And don’t be surprised if you hear the rumble of thunder when a series of downpours and storms come your way in the late morning.
When does it all expire? It looks like precipitation is slowly pushing east in the evening, with an overnight drying trend. Temperatures will also return to normal and by the time you wake up on Saturday will be below freezing for most of the region. Fortunately, the 30s will be a much quieter weekend with clear skies and heights on both days.