Fig. 1: Cold air scare! The upper air forecast days 11-15 in the northern hemisphere identify the ridge bridge over Alaska and a Canadian polar vortex.
Fig. 2: All models…West Pacific Oscillation forecast through 15 days. Note the super negative signature of the GFS forecast!
Discussion: Natural gas prices jump from $2.45 to $2.65 since Sunday night largely in response to potential much colder air ahead for February. Last night the 0000 GMT GFS model identified the concern. A near-perfect set-up with a ridge bridge over Alaska causing low level arctic air to travel from Siberia cross-polar and into North America (Fig. 1). Meanwhile, the ridge bridge is compensated for by a deep polar vortex over West-central Canada certainly capable of generating arctic air and gathering intensification from the cross-polar flow. The cold air generating upper air pattern is best seen by a super-negative West Pacific oscillation (-WPO) in the extended-range (Fig. 2).
The West Pacific oscillation forecast chart does reveal the problem with this forecast. The GFS is on its own especially in the 11-15 day forecast as the WPO index is flat according to all other models.
For the moment, lets take a look at the most likely upper air forecasts in 15 days based on the mega-cluster ensemble. The most likely scenario (44% confidence) is a polar vortex positioned over Canada which would leave the East U.S. mild (Fig. 3). The second-most likely scenario (29% confidence) is a polar vortex over Central Canada which would create sharp cold but south and east of this regime the East U.S. stays mild (Fig. 4). The third-most likely regime is persistence…a cold trough over snow-covered West U.S. while the East stays mild (Fig. 5). The mega-cluster day-15 upper air forecast is valid for Feb. 9-10.
There is some brief stratospheric warming across northern Canada around day 10-11 but very transient in nature. A longer duration stratospheric warming event would justify the cold GFS forecast.
An index to watch over the next few days is the West Pacific oscillation (WPO) and the East Pacific oscillation (EPO). These indices when very negative identify presence of a “polar vortex” regime.
For now, the ridge bridge/polar vortex cold pattern has about a 20-25% chance of occurring.
Fig. 3-5: Mega-cluster ensemble most likely day-15 upper air pattern across North America.