A fascinating pattern change is upon us and we’re going to see a fairly abrupt change in our weather. We can actually trace it all back to a weak system that brought us a bit of rain the weekend after Christmas. Remember that storm? You probably don’t since it was a pretty easy to forget!
That innocuous storm in New England developed into a monster storm over Iceland with a pressure around 930mb prior to New Years. You can see in the surface map above the sprawling storm retrograded into Iceland and took up a large chunk of the North Atlantic. This system was so powerful it effectively managed to shake up the atmosphere over the Arctic. A large cyclonic wavebreak occurred sending low potential vorticity air north toward the North Pole – substantially increasing the height of the Dynamic Tropopause over the Pole.
This wave break and associated ridging has shattered the positive Arctic Oscillation pattern that had been so dominant in December. This graph of the AO courtesy of Ryan Maue at WeatherBell shows the dramatic shift from a positive to a negative AO regime.
Ridging over the Arctic (-AO) is expected to continue through the next 10-15 days which should give us several bouts of below normal chill and with some luck a snowstorm. You can see that ridging here by day 10 on the Euro Ensembles with a mean trough over the northeastern U.S.
Getting a snowstorm around here takes a bit of luck – though the pattern does support a wintry period. Our first shot comes this weekend and early next week though at this point I’m not overly excited with our first opportunity in the Saturday-Monday time frame.
Here’s a look at the Monday system on the European ensemble and you can see a strong signal for a northeastern U.S. coastal low but the lack of any appreciable high pressure/confluence to the north. Outside of the elevated interior a nice cold and dry high is always an important ingredient.
Whether or not the storm threat in the 1/9-1/11 window pans out with a snowy solution the pattern looks good for winter weather going forward – through at least 1/20.