Saturday, December 22, 2012

Long Range Lookout, Apocalypse Edition: Stormy Pattern Continues, Cold Outbreaks Likely

**This post is dedicated to Ana Marquez-Greene, age 6, a victim of the Connecticut shootings.**

This edition of Long Range Lookout was published on the Apocalypse, December 21, 2012.

The stormy pattern that many have recently experienced should continue, and increasing cold patterns should emerge as a response.

The above image shows a side-by-side forecast from the ECMWF model (left) and the GFS model (right). The forecasts are for the 500mb height anomalies from the Day 8 to Day 10 forecast period. We'll start with the stormy potential. See that low pressure anomaly over the West US? That is a negative Pacific-North American index (PNA). In the negative PNA, you'll see storm systems forming over the Southwest and propagate through the Plains before going somewhere in the Central and East US. This negative PNA has been present in the last few weeks, creating several stormy situations over parts of the nation. As long as this keeps going, more storms will continue to appear, some of them significant.

The second thing is the rampant reds over the Arctic. This signifies a negative Arctic Oscillation. In a negative AO, high pressure forms over the North Pole. This high pressure weakens the polar vortex, a permanent low pressure system that regulates the flow of cold air that stays and leaves the Arctic. In a negative AO, cold air is more prone to escaping the polar vortex and fleeing south into lower latitudes, including North America. The PV may be weakened so much it could crash, and more on that can be found in this link.


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