You want the “Pacific Products” page and select the charts for the “North Pacific Surface Analysis”.
Next choose the 21 day loop (at the time of writing it is still on the 7 day loop, if your connection is a little slow but you aren’t.)
What you see as 21 August approaches is a modest anomaly.
Ordinarily the Gulf of Alaska houses the Aleutian Lows before they go ashore to water North America. With an extensive Antarctic ice sheet the surface pressures are not very different for Lows and Highs.
In northern waters pressure differentials can be quite striking. In the charts showing at present, a sea surface pressure of 1016 millibars constitutes a cyclone and one of 1028 mb an anticyclone.
Now look at the blocked situation on the west coast of North America. When a Low pushes through two fairly far apart anticyclones, tornadoes tend to dominate the following phenomena lists.
When the anticyclones are virtually connected as is the case with the egg-timer shaped system off the coast in the link, then the situation is relieved as volcanic events predominate.
On the 20th of August 2014 a cyclone does pass through two fairly widely spaced anticyclones:
With the whole of the northern hemisphere experiencing unusually flaccid pressure differences (a period of low “Pressure Gradients”) the number and ferocity of tornadoes in North America is very mild. At the same time the development of Atlantic hurricanes seems to be put on hold.
I really can’t go along with interpretations of the Gilbert Walker cycles climatologists maunder on about these days. The Wikipedia article on the North Pacific systems is almost undecipherable to me. I have the greatest respect for Sir Walker though. His work at the Indian Meteorological Office was splendid:
Sir Gilbert Thomas Walker, CSI, FRS, (14 June 1868 – 4 November 1958) was a British physicist and statistician of the 20th century. He is best known for his ground breaking description of the Southern Oscillation, a major phenomenon of global climate, and for greatly advancing the study of climate in general.
But I am seeing something else. The problem is that statistics merely “point towards trends” they do not tell anyone what is actually happening. Climatology has its place although I tend to avoid the subject like the plague. In weather forecasting we have:
Actual data on Analysis charts
“Butterflies” pointing to all sorts of possibilities on Forecast charts and…
Here is the US storm report for the 20th of August 2014:
August is a time for Atlantic hurricanes not US tornadoes and whilst there is a marked absence of both in 2014, this chart at least shows that the winds in North America in this spell were strongest on the 20th.
You can check for yourself on this link: http://www.spc.noaa.gov/climo/reports/140801_rpts.html
As you can see, we are only on the fourth hurricane this season. It started in June and runs through to November. Normally we have had half a dozen by now. However it doesn’t fit any particular cycle to only compare data for one phenomena over a number of years; one has to take into account other geo-phenomena, that is the point of failure with statistics.
Compare the years 2005 with 2006 for example or 2013: