No, we aren't crazy, thanks. Over the past few days all of our forecasters have been intently watching the model guidance as it continues to hint at a large arctic outbreak of cold air across the Eastern portion of the United States. Finally, I think we have reached the consistency necessary to actually mention it. Without getting to deep into this, lets state the facts. The cold will likely be brought in by an array of indexes lining up to support the atmospheric pattern capable of bringing in arctic cold at this time of the year.
Firstly, Model consensus continues to indicate that a very strong Positive PNA ridge will develop over the next week or so. A positive PNA can be associated with a large ridge over the Eastern Pacific of Western United States, often extending as far northward as western Canada. This is shown on the latest NCEP index ensemble forecast to the left, where we can see a rapid increase in a PNA that has been mostly negative over the past few weeks. This spike is evident on latest 
forecast models, particularly the GFS and its ensembles, where we can see the beginnings of the Positive PNA being shown to the left. This is coinciding with the forecasted PNA spike, and the ridge in the western US winds up strengthening throughout the forecast period (though that is pushing it into GFS Long Range territory...a line we will try not to cross).
Another important facet to the possibility of this cold outbreak will be the progression of the NAO or North Atlantic Oscillation. The NAO recently spiked towards positive on or around October 15th or so, and is currently at or about a +.8 state. However, we can turn out attention to the tropics for a major development here. Forecast guidance suggests that Tropical Storm Noel will race Northeastward in the Western Atlantic, becoming a very strong subtropical area of low pressure as it does so. As it heads northeast, Noel is forecasted to put in a major piece of puzzle. Forecasts indicate that Noel will actually nudge a ridge northward, coinciding with movement eastward of Greenland. This supports the latest ensemble forecasts of a steadily decreasing NAO state into November. Highlighted in the pink circles are two main areas of concern. The first, already mentioned (the decreasing NAO state). The second is the fact that actual NAO verification has been running on the high side of ensemble forecasts. This definitely needs to be taken into account.
All of this data clearly supports a western ridge developing by early November, with a resultant deepening east coast trough. Whats alarming at this point, however, is the amount of data pointing to this solution and the extremities they present. For example, to left is todays 12z NCEP GFS Ensemble mean output. To see these types of departures and this type of consistency over the past few days definitely deserves some attention. Yes, things could change, but at this point all of us feel the threat for a cold weather outbreak in the northeast is increasing as the days go by. On a side note, one of the forecasters (not sure who yet) will have a NYC local weather update by 10pm or so this evening with a complete forecast for the week. We'll also make sure to update on the cold as it draws nearer.
Firstly, Model consensus continues to indicate that a very strong Positive PNA ridge will develop over the next week or so. A positive PNA can be associated with a large ridge over the Eastern Pacific of Western United States, often extending as far northward as western Canada. This is shown on the latest NCEP index ensemble forecast to the left, where we can see a rapid increase in a PNA that has been mostly negative over the past few weeks. This spike is evident on latest 
forecast models, particularly the GFS and its ensembles, where we can see the beginnings of the Positive PNA being shown to the left. This is coinciding with the forecasted PNA spike, and the ridge in the western US winds up strengthening throughout the forecast period (though that is pushing it into GFS Long Range territory...a line we will try not to cross).
Another important facet to the possibility of this cold outbreak will be the progression of the NAO or North Atlantic Oscillation. The NAO recently spiked towards positive on or around October 15th or so, and is currently at or about a +.8 state. However, we can turn out attention to the tropics for a major development here. Forecast guidance suggests that Tropical Storm Noel will race Northeastward in the Western Atlantic, becoming a very strong subtropical area of low pressure as it does so. As it heads northeast, Noel is forecasted to put in a major piece of puzzle. Forecasts indicate that Noel will actually nudge a ridge northward, coinciding with movement eastward of Greenland. This supports the latest ensemble forecasts of a steadily decreasing NAO state into November. Highlighted in the pink circles are two main areas of concern. The first, already mentioned (the decreasing NAO state). The second is the fact that actual NAO verification has been running on the high side of ensemble forecasts. This definitely needs to be taken into account.All of this data clearly supports a western ridge developing by early November, with a resultant deepening east coast trough. Whats alarming at this point, however, is the amount of data pointing to this solution and the extremities they present. For example, to left is todays 12z NCEP GFS Ensemble mean output. To see these types of departures and this type of consistency over the past few days definitely deserves some attention. Yes, things could change, but at this point all of us feel the threat for a cold weather outbreak in the northeast is increasing as the days go by. On a side note, one of the forecasters (not sure who yet) will have a NYC local weather update by 10pm or so this evening with a complete forecast for the week. We'll also make sure to update on the cold as it draws nearer.
Comments
0 Response to 'Early/Mid November Cold Shot Chances Growing'
Post a Comment