Northern Hemisphere: 500mb Past 30 days
The Polar Vortex is a naturally occurring flow of air around the North Pole.
In normal conditions, the coldest air is locked up within it. But a weak Polar Vortex can be disrupted to wobble or split, allowing arctic air to spill southward into North America, Europe, and Asia.
The Arctic Oscillation is an index in essence connected to the normal easterly winds in the higher latitudes.
When they weaken or reverse, a NEGATIVE index would be measured. This would allow colder air to spill southward.
North Atlantic Oscillation is a measure of the slow or blocking of winds in the North Atlantic.
When a Block develops, often in Greenland, then arctic air has a better chance to reach the eastern US.
This also disrupts the jet stream to produce more frequent and perhaps stronger coastal storms.
Global circulation can often be seen as waves of ridges and troughs. We measure them aloft at constant pressure levels to see how the height changes.
This 200mb level is located roughly 39,000 feet above the ground.
Sea Surface Temperatures are obtained from remote buoys and satellite measurements.
Anomalies are a comparison of measurements to a 30 year average.
This is valuable in determining warming or cooling trends, that can identify an El Niño or La Niña.
The tropical Pacific is broken down into regions. Compare the numbered plots to the locations in this map.
MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average. This atmospheric disturbance is distinct from ENSO, which once established, is associated with persistent features that last several seasons or longer over the Pacific Ocean basin. There can be multiple MJO events within a season, and so the MJO is best described as intraseasonal tropical climate variability (i.e. varies on a week-to-week basis).
The MJO consists of two parts, or phases: one is the enhanced rainfall (or convective) phase and the other is the suppressed rainfall phase. Strong MJO activity often dissects the planet into halves: one half within the enhanced convective phase and the other half in the suppressed convective phase. These two phases produce opposite changes in clouds and rainfall and this entire dipole (i.e., having two main opposing centers of action) propagates eastward. The location of the convective phases are often grouped into geographically based stages that climate scientists number 1-8.
Regions 7, 8, and 1 are historically more favorable to feed a storm track to the west coast of the US. Sometimes coordinating for east coast storms as well.