This is a run of combined forecasts called an EFS for Mexico USA and Canada. Various runs are made with the models used and the combined output is shaved from a plate of spaghetti outputs to this one organised forecast. The daily run goes out to the analysis time+360 hours in 24 hour intervals.
Above is the last chart for August and the first for September 2014. The Lows or cyclonic systems are weak and ill defined. The anticyclones or highs are much stronger.
But the spell changes and the anticyclones split into smaller systems after forming ridges and leaking away.
Note that when an anticyclone declines, the air doesn’t join the cyclones but persists in much the same area as before -if it can.
In fact cyclones and anticyclones tend to follow routes defined by something divorced from what mere isobars show us.
What happens when three Lows (or three Highs) occur on such a chart is somewhere on the planet the isobars are operating deeper in the planet.
It could be that these subterranean pressure points coalesce or join up to form an earthquake of large magnitude or there might be a volcanic eruption of notable output.
In such cases the pressure systems are better defined than on these charts but (for volcanic eruptions) they tend to last longer. When they lie adjacent, such as the 5 Lows in the chart above, it is a sure sign of a significant event.
Look at the chart one above that. There are three Lows adjacent and also three Highs.
This one is a confusing signal. Generally when that happens the eruptions, if any, are low key or there are several low-medium sized earthquakes.
Take a look at what earthquakes were occurring on the dates of these charts and see what you can make of things:
As a general rule; when we get a series of alternate systems (H/L/H/L etcetera) there tends to be a series of quakes in the range of 5.5 to 6 .5 M.
You can usually see it all coming a few days in advance. But you can’t rely on these model runs because they are not changed by computed progression alone.
There is a lot of human input correcting what the meteorologist knows from previous experience won’t happen, or from simple gas physics, can’t happen.
But when three or more well defined systems line up as with the product above, then you should pay more attention than usual to what happens next.
If the chart is a one off, then the signal means a large eruption is due. If you check with other charts you can tell if this is an error or something else is happening off the page.
I called a dud on the above thinking it was a larger than usual quake due. But there must have been another adjacent low in the mix off-screen.
Volcanic activity had increased for these dates but it wasn’t widely reported until journalists stopped blathering about Iceland long enough to report what the Philippine authorities were doing about Mount Mayon.
Not that you would know it from these runs. But I have omitted all the charts from the NAEFS except these 24 hour forecasts.
A series of large medium sized quakes occurred with the above:
2014/09/17 6.7 M Mariana Islands
2014/09/17 5.6 Mb Vanuatu Islands
2014/09/16 5.6 Mb Eastern Honshu, Japan
2014/09/16 5.6 Mb New Britain, Papua New Guinea
From now on the volcanism gets serious:
Which brings us pretty close to the end of the spell. In the next thread I will discuss the same signal and what happens then, according to the Australian charts.