With the drought and wildfires being the biggest weather story of Southern Colorado and adjacent states to the south and southwest, it has a lot of people asking: Will the monsoon fail?
This is a difficult question, but something that we don't need to worry about yet. The extreme drought to our south and southwest do not bode well for significant relief in the near term. Drought of this magnitude is a terrible thing to break, but it has happened. We dealt with major drought in the spring of 2006 and it started raining on July 1st of that year. That drought was over... However, in the summer of 2006 we were coming out of a La Nina and going into an El Nino. Is the same true now? Let's look...
As you can see, La Nina peaked last winter and we are in neutral territory right now. We may even flirt with weak El Nino staus in the next couple months. However, the ECMWF model and various other models I have looked at suggest we will go right back into La Nina this fall and winter. My own experience suggests the same will happen. The year following a powerful La Nina will usually be marked by a weaker La Nina. I believe the fall and winter of 2011-12 will be no exception.
What I have written above does not bode well for an extended monsoon. If we were to keep a weak El Nino around for a longer period of time, I would begin to think that July through early September may be pretty wet. However, I don't think this will be the case...
Enough about El Nino and La Nina...what about the main driver in the monsoon. Here is the pattern shift that takes place in late June and early July:
Normal June pattern has the High Pressure over Mexico. This shoves the moisture to the south and keeps it there. By July, the High builds northward over the central US. This draws the moisture up from the south and southwest, interacts with daytime heating, and gives us the nice soaking rains of mid to late summer. If that High doesn't build north, the moisture stays south and we are in trouble.
Here is a nice water vapor image during a good monsoonal pattern:
All that white shading is moisture that streams up from the Pacific Ocean. Notice the bright white over Arizona, New Mexico, and Southern Colorado. Classic monsoon pattern that develops once that all important High moves a bit to the north and east... Remember, this pattern shift usually happens in the next 3 weeks.
So it isn't quite panic time yet. In fact, many times hot and dry weather will actually help induce the monsoonal flow earlier than normal. I don't think this will be one of those years, but I do think the pattern shift likely won't occur until at least early July. If this pattern shift does not occur in the next 3 weeks, then I would start to panic.
Officially, I am calling for about two months of decent rain chances and then likely back to drought conditions for fall, winter, and early spring of 2012. Beyond spring of 2012, I think an El Nino will be in order and we can put this drought talk to bed...at least for a while.
Chief Meteorologist Brian Bledsoe