This has been as much of a “non-Winter” as we’ve seen in many years. Last Winter season’s -NAO, + PNA and -AO, which promotes ridging in an ideal location of the intermountain western US, movement of cold arctic air into the US, and blocking of cold air into the eastern US, has been absent this Winter season. Instead, a very strong low pressure vortex has been locked into Alaska, preventing the development of a +PNA(no ridging in the mountain west, allowing cold air to flow down from Canada). Please see attached image, showing the results of a positive and negative AO, PNA and NAO. I have been caught by surprise, by the turn of events. Also, second year La Nina’s sometimes have led to cooler Winter temperatures in the eastern US, IF the atmospheric indices function properly. Obviously, that hasn’t worked out this Winter.
Where do we go from here? It appears that, FINALLY, we are seeing consensus among the computer models of a developing +PNA, and in conjunction with a -AO(see images attached), we should see a high pressure ridge build up into Alaska over the next 3-5 days, replacing the powerful low pressure vortex that has been located there since November. This should provide a path for cold air to come down into the eastern US, and should form a sharp trough into the eastern US, potentially leading to a cutoff upper level low pressure system in the southern US, or potentially, a cold air damming event, for the end of the upcoming week, as a strong high pressure cell moves into the northeastern US, funneling cold air down the Appalachians, into NC, upstate SC and NE GA.(see attached images)
From there, the GFS model, European model, and Canadian model, all show the same configuration lasting through at least the first 15 days of February, providing potentially multiple opportunities for Wintry precipitation in the southern and eastern US. The lack of a -NAO(see image attached), in combination with the subtropical jetstream coming across from the SW US, argues for storms coming across the southern US and out to sea. At the least, this pattern should provide for colder than normal temperatures for February, after being 5 degrees over normal for December and January. I am including model depictions of the potential upcoming upper level low pressure and CAD(icestorm potential) scenarios that are showing up for next weekend, as well as the +PNA(roller coaster).
I’ll keep you updated, but I think we need to look for Winter time coming up after a mild to warm first half of the week.
Image of positive PNA. Notice the warm colors over the western US and into Canada, which depicts the high pressure ridge and the cool colors over the eastern and southern US, which depicts a low pressure troughing area. This corresponds to cooler than normal temperatures for the east and south(courtesy of State of North Carolina Climatology Office).
The next image reflects a negative AO(Arctic Oscillation). This promotes movement of air from the Arctic area into the US. Notice the cool blue colors representing cold air(courtesy of State of North Carolina Climatology Office):
This image depicts a -NAO(North Atlantic Oscillation), which is not present heading into February(courtesy of NOAA airmap). Note how cooler air and troughing occur in the eastern US, along with cooler temperatures: