WIndow of opportunity: January 7-9th

As this year peeters out with no measurable snow in December for the second year in a row, the new year seems to have hope. So far this winter, the pattern has been pretty bad for snow. With a upper level trough out west and a ridge over the south east, storms have been allowed to cut west of us, putting us in the warm sector.

This is why Christmas was so warm. Ridge over the Eastern US resulting in very warm temperatures.

With the coming of the new year, computer models are suggesting that multiple features in the atmosphere will line up in a way that will give us a chance at snow next weekend. First off, so far this winter, there has been a persistent trough (upper level low pressure) associated with a dip in the jet stream out west. Generally, this would mean that the jet stream would compensate by rising up (ridge) over the east. This setup results in cold out west and warmth in the east. It all matches up. Now farther east over the Atlantic, there is also a trough over Greenland. What we want there is actually a ridge. We also want a ridge over Alaska. The Greenland ridge buckles the jet stream over the eastern US, forcing a trough there and keeps us on the cold side (known as blocking). the Alaska ridge in conjunction with the Greenland ridge displaces the polar vortex southwards over Canada, supplying cold air. This is out set up. Now we just need a storm to enter the mix.

Note the Alaskan and Greenland Ridges (reds) as well as the N. Americna trough (blue) on the GFS ensemble mean. This is a decent pattern for a storm

On paper, it's all very simple, but there is a balance. Too much PV displacement and the storm is suppressed, shoved south by the cold. Congrats NC. If the AK ridge is too far west, then the jet stream is allowed to rise back north resulting in us being on the warm side of storms. Same goes if the Greenland block fails to materialize. At this range, ensemble models with many members run at different initial conditions can allow us to assess the possible outcomes which is more accurately than looking at a single operational model runs. Currently, there are two possible storms that the models are keying in on with a mix of solutions mostly either hitting us or missing to the south, which is a good place to be right now since the trend for this year is to the NW as lead time decreases.

People with plans for that weekend should be on the lookout (Robotics Kickoff I'm looking at you). In terms of potential, the upper end is probably around 6-10" due to it progressive (flat and fast) nature of the setup. However, the details are still being ironed out since the timeperiod is still over a week out and believe it or not, models can suck at long lead times. Timing is a critical factor and if the storm is too fast or too slow, it could miss the window of opportunity. At this point  I'm happy to have a storm to track through a good setup. I'll keep you posted.