North American Monsoon

savj2

Hi folks. My first post on boards.ie but love reading this forum.

With the South-West USA going through a drought with extreme heat is there a sign of the North American Monsoon arriving any time soon? I thought the North American Monsoon arrives in July and stays until September.

From checking weatheronline.co.uk we can see a jet stream dip over the central USA which seems to be dragging all the moisture to the South-East of the USA

What is required for the monsoon trough to move northward from Mexico into the South-West USA? Does that Jet stream need to straighten up move back to the north, or does the Bermuda High need to strengthen more over the eastern US?

I would be interested in your thoughts and analysis on this.

M.T. Cranium

The monsoon effect tends to come and go over the course of most summers in the desert southwest region. The reality is that thunderstorms occur about two thirds of all days at least somewhere in the region (roughly defined as AZ-NM-s NV-s UT-sw CO) and some of them are more typical of cold fronts elsewhere, while at other times a monsoonal pattern spreads further north into parts of eastern OR-WA, much of ID-WY and parts of MT.

It's not often a situation described as either-or but instead a matter of coverage, slight, considerable or widespread. When it becomes "widespread" the storms often come away from their usual higher elevation haunts and rip through more populated valley locations such as Phoenix and Las Vegas. Another defining characteristic of monsoonal storms is that they track west or northwest but sometimes even southwest. However, having been in the region in a fairly active phase (Aug 20-23, 2011) I can say that the cells tend to rotate around a centre of upper high pressure wherever that happens to be located and the most likely position of one seems to be near the middle of Colorado. This gives the monsoon in Utah and Nevada more of a south to north orientation.

I found out that people in the region tend to speak about the monsoon in very localized terrms. The 2011 monsoon was fairly normal in large-scale terms but as all cells had missed the town of Kanab in southern Utah, somebody there told me that it was a poor year for the monsoon. Yet that same day we were chasing two different storms within a hundred miles of there.

savj2

Thanks for that information MT Cranium. That Upper Level High over Colarado makes sense as it would steer moist winds in from the Gulf of California. The area needs rain badly. So would August be typically be the most active time of the year for Thunderstorm activity in the South West particularly in New Mexico, Arizona and California?