Monday, December 19, 2016

Monday Morning Pattern Update: A Turn in the Tide

Good morning everyone. Well, the weekend storm system ended up being a mess as mostly predicted. The snowfall amounts hit the lower end of my range barely. In NJ the highest amount I saw was 5" all the way up in Sussex county but other areas got 2-3" with less to the south. That includes the ice that fell. Overall I give myself a C on that forecast.

Lets move on to the overall pattern over the next two weeks. Here is a summary of my talking points:

  • Cold air over the region today filters out by Wednesday giving way to more seasonable conditions
    • Seasonable means low to mid 40's for many areas
  • As we head to Christmas weekend things get a little warmer with temperatures going towards the upper 40's for highs
  • The weather pattern then maintains its current transition to seasonable-mild through at least the New Year
  • This means limited chances at winter events during this time period
  • Major question marks remain if and when this transitions back to a colder and stormier set up
  • We need to take this one week at a time as models have struggled this year
So lets dive into details. When we look at what the weather pattern has in store we always look up to the flow of the jet stream and in particular high and low pressure areas at 18000ft. As we head into the next two weeks a distinct pattern of lower than normal pressures in the west, higher than normal pressures in the east and more importantly lower than normal pressures over Canada...

This is the opposite pattern of cold and snow for the east. We have no high pressure over Greenland (+NAO)) or the pole (+AO). This alone gives cold air the chance to stay locked up to the north. We also have no high pressure over the west (-PNA). This allows a ridge of warm air to rise along the east. I will note, this is not a complete blow torch of warm as the pattern in the pacific is still wavy meaning its not a complete fire hose jet screaming across the whole country. Areas like New England mountains can still see snow in this pattern.

What is concerning me along with these model projections is the changes in the stratosphere. Most models now all project the stratospheric vortex strengthens over next week or so. You can see this below..

This influences the pressure pattern lower in the atmosphere. When you have a cold and strong stratosphere like seen above, it results in lower pressures over the pole which helps keep the cold air locked up to the north.  

All these factors line up to make the teleconnections look as bad as they can possibly be..

A -PNA means low pressures in the west, a +NAO means low pressures near Greenland, a +WPO means low pressures in the northwest Pacific and finally a +EPO means low pressures in Gulf of AK. Again, not the pattern for winter in the east. 

It will be critical to see if as we head into Jan if this trend starts reverse. It certainty is not out of the question that it can. Many winters have periods of mild weather followed by winter returning. What is bothering me however is that we barely experienced winter in the Mid-Atlantic so far this season. Sure we had a few big cold shots and SOME winter precipitation but nothing very widespread. I would be lying if I said December was a memorable so far.The country as a whole was very cold and our area has been colder than normal but this will moderate before December ends. You can see below temperature departures from normal so far this month..

MUCH different than last years historical warm December..

At the end of the day when we look back on this current month given the moderation coming, we will say it was OK. 

So as we enter January its more of a wait and see mode. IF we get high pressure over Greenland (-NAO) I believe despite the lack of high pressure or riding over the west coast this winter will deliver in the east. We just do not know yet at this time if that will occur. The models are trying to show it develop in January as seen by the red over Greenland below..

This would not be a horrible pattern believe it or not. The issue is I do not trust these long range models. We need to take this one week at a time this year.

Bottom Line: The pattern will moderate over the next two weeks and it remains to be seen how things turn out after then. I am not calling winter off I am just pointing out my current observations. 

I am sure a few surprises will be thrown our way.

Thanks for reading. 


  1. Isn't it true that even the Polar Vortex does not have an endless supply of cold air and needs it to be replenished somehow to continue producing cold air? That somehow meaning migrating to near the Pole where conditions exist to allow recharging of the cold air. In that context a strengthening Polar Vortex is not a "bad thing". Further, if and when the Polar Vortex affects the Eastern lower Latitudes, it's usually during mid January or February-not December. The unfortunate problem for this winter is that we are not getting any cold from Canadian high pressures and have to rely on cold from the Polar Vortex, which is not good for winter weather enthusiasts. Hopefully then, the low Arctic sea ice will cause another SSW sufficient enough to weaken the Polar Vortex and it migrates towards Eastern Canada and the US this time. We cannot depend on cold Canadian highs this year for cold and snow I fear.

  2. दिल्ली में रिकार्ड सर्दी, पिछले पांच सालों में सबसे ठंडा दिन रहा रविवार