Stratospheric Warming Event Evolving for Last 1/3 of January is impressive.
Beginning now, we’re in close monitoring of the GFS sending arctic air cross-polar and into North America let this month.
Fig: 1: An extraordinary view of stratospheric temperature anomalies in 16 days by the GFS forecasting an awesome warming event on the Eurasia side of the North Pole.
Discussion: Stratospheric warming is forecast to develop and expand in the polar region, the last third of January. In 16 days, the GFS indicates a powerful warming event taking place mostly on the Eurasia side of the North Pole (Fig. 1). However, the stratosphere is still cold across the U.S. and eastern North America therefore the arctic air at ground level generated by this event is not easy to forecast by various dynamic models. The overnight GFS has the arctic air generation that should emerge from this event indicating 40-50F below normal in Siberia. However, the GFS is not consistent with this cold extreme and other models are cold but not arctic cold.
So, problem number 1 is whether extreme cold develops (or not) in Siberia due to the stratospheric warming event. This region is a major source region for strongest cold risk to North America. My opinion is that the extreme cold GFS solution of last night is correct and 40-50F below normal temperatures will emerge in Siberia in the 11-15-day period.
The GFS 11-15-day upper air forecast (at 500 MB) indicates a ridge bridge, similar to the pre-Christmas event, forming over Alaska extending poleward (Fig. 2). The upper ridge is sufficiently positioned to at least allow arctic air to bleed into North America during this time. The ridge pattern is not quite positioned to deliver a Siberia Express into North America (but its close).
So, problem number 2 is air mass trajectory and delivery potential to North America. The GFS is stating the delivery process to take the Siberian air mass into North America is almost there. Other models are timid, but given the extent of stratospheric warming, the potential for a scary set-up is certainly there. The GFS is likely the first model to flush frigid arctic air into North America. Timing is uncertain, however.
Problem number 3 is timing the cold outbreak due to the sharp reaction of natural gas markets. Right now, the GFS shows potential while other models are timid. Because arctic air is so low-level in character, the models have a hard time identifying the outbreak risk especially beyond 10 days. Beginning now, we’re in close monitoring state of alert for a sudden explosive arctic air outbreak by GFS. The ingredients are becoming more supportive but are nowhere near perfect yet.
Fig: 2: GFS 11-15-day upper air forecast for the northern hemisphere.