As I watched the radar animation for the Southwest this morning, I was surprised to see a large cluster of thunderstorms near Tucson moving south. This is not anything like normal monsoonal activity. The answer is Hurricane Dora. She is sucking in everything around her this morning. Hurricanes effect not only the local weather in the storm, but the weather for a 1000 miles away. Dora is going to help clear us out for a couple days, then provide moisture back this weekend.
This week has been wonderfully comfortable. Maybe it has been too breezy, but the winds have been lessening. While the headlines are all about the East baking in the summer sun, the West has racked up low temperature records. For June, the daily highs have been as low as 8 degrees below normal for Flagstaff. It’s an interesting situation.
It is all about to change. Temperatures should climb closer to our normal highs by this weekend. Next week, we should see those temperatures be with in a couple degrees on the high or low side of 80. The winds should decline overall. We may still have another bout or two of breezy days. Remember, it has to get hot to fire up the monsoon.
Another interesting thing is Hurricane Adrian. Remember, hurricanes can affect the weather for a thousand miles from their core. I am afraid Adrian will impede the flow of moisture toward Arizona. This flow should be starting.
The National Weather Service hasn’t published their review for the month of September, yet. But, I think it’s a pretty easy month to summarize. Here is the monthly climate graph from Weather Underground.
There were two stormy times, from September 6-9 and September 22-23. These provided us with significantly cooler temperatures for several days. The rest of the month was absolutely beautiful. It was the best month this year to get outdoors and enjoy. As you can see the last week of the month was well above normal for temperatures and drove us firmly into an above average temperature month. Overall, according to the National Weather Service, we were 2.4deg F above normal with precipitation coming in at a meager 0.79 inches, 1.33 inches below normal. This shift in temperature represents a strong move in the departure from normal temperatures since 2004.
Temperatures have been mostly below normal since the fall of 2009.
September 1998 doesn’t match September 2010. I think this is due to the timing and rapidity of the shift from El Nino to La Nina, and the accompanied change from a warm Pacific Decadal Oscillation Index to a cool one. I think this has led to a faster return of dry, and possibly warmer conditions. Notice the large cool body of water in the Equatorial Pacific.
Also note the warm North Atlantic Ocean. As an aside, there are a couple cooler patches of water in the North Atlantic. One from the coast of Africa stretching north of the Caribbean towards the East Coast of United States. The other from the coast of Nova Scotia to the east. These are under the tracks of Hurricanes Earl and Danielle, and Tropical Storms Colin and Fiona. Tropical storms provide this cooling.
The warm Atlantic and the cool Pacific are going to be the drivers for our upcoming dry winter.
Heavy Rain is expected today. As always, some may get a little, some may get a lot. But, we have a new edition to the scenario, Tropical Depression Georgette.
Tropical Storm Georgette formed yesterday out of a low pressure system. As she moved north over Baja, she weakened to a Tropical Depression. She may return to tropical storm force winds as she moves during the day. She will weaken further as she rapidly continues to Arizona.
Today’s rain is not directly associated with Georgette. Many areas could still see rainfall amounts of over 0.5 inches. Some over 1 inch.
When the weather is this beautiful. Last week was a little chilly, but this week is near perfect. The controlled burns are destroying some of that perfection with smoke lingering around town over night.
The big question in my mind is whether we will see any precipitation in the rest of September. Enter tropical Storm Karl. Currently, there are 3 named storms in the Atlantic area. Tropical Storm Karl is in the Caribbean.
Will Karl’s moisture and low pressure make it to the southwest? The long-term GFS Model has been vacillating between yes and no. Currently, there is a chance the moisture will make it across Northern Mexico and into Arizona around the weekend of September 25-26. However, model to model runs shows differences in the strength of the westerly flow across the state at that time. If we have strong westerly or southwesterly flow, then the moisture will be blown to the east. Something to watch.
In the mean time, enjoy the beautiful fall weather.
Well, La Nina isn’t looking like it will back-off in time for winter. The typical La Nina effects for Northern Arizona are slightly warmer than normal (near normal) temperatures with substantially below average precipitation.
1998 continues to look like a reasonable analog year. Both ENSO (El Nino Southern Oscillation) and the PDO (Pacific Decadal Oscillation) moved strongly to the cool side. They are forecast to stay cool for the winter. However, I think the move this year happened a little earlier than 1998. This gives some concern about the onset of the changes as a result.
The tropical storm season in the Atlantic got off to an earlier start this year than in 1998. Still, the number of storms could be very similar. In both years we have strong clusters of storms forming in early September. The early start makes me wonder about the precipitation in the fall in Arizona. Hurricanes and tropical storms can limit the flow of moisture to the region. At this point it looks like the Monsoon Season is over and the typical fall and winter weather pattern has begun. This pattern has storm fronts sweeping through and past Arizona.
September and October had above average and near average precipitation amounts in 1998. Right now, it doesn’t look like we will see anything for a couple weeks. I still think there is a good chance for near normal precipitation in September and October. However, the earlier transition from El Nino to La Nina could mean we will see an earlier chance to dry conditions. Temperatures in these months should be pretty close to normal, I think.
So, where does that leave us for the winter? Sorry folks. As of the start of September, it appears this winter will be near climitological normals for temperature. Now, the global outlook is for a colder than normal winter. This may cause Northern Arizona to be colder than normal. I’m just not sure. I doubt it will be warmer. This cooling trend is being driven by a very weak solar cycle among other things.
On the precipitation side, we will be dry. Probably very dry. December – February may see precipitation totals of less than 1.5 inches. I won’t be buying a season pass at Snowbowl. Then again, I never buy one. I just don’t get up there enough.
Is there a chance for change? Can I be out to lunch? Sure. Rapid changes in the sea states linked to ENSO and PDO are possible. Last year at this time, most thought El Nino would fade before winter. It didn’t, and we had a wet winter.
postscript: I installed a heated sidewalk this summer. This almost guarantees a dry winter, right?
This picture tells the tale of our weekend. But, does it foretell our future? Is the monsoon season coming to an early, wintry end?
As you can see, the jet stream has dipped far to the south in an almost winter pattern. This dried out our air and dropped our temperatures. Yesterday’s high in Flagstaff was 72F, six degrees below normal. The air is substantially drier as seen in the water vapor image below.
The jet stream is drawing the dry air from over the cool waters of the Pacific Ocean. This has completely shutdown the monsoonal flow. What does this mean for the long-term? I still think 1998 is the model year. The Altantic Hurricane Season is in full swing right now. Danielle and Earl are named. In the chart below, note that the names Danielle and Earl were also used in 1998. Also, note that they occurred in late August and early September. There is another area that has a high likelihood for development in the Eastern Atlantic. Behind all thosee, there is a line of disturbances across Africa that are marching to the west. Each has a good chance at developing into a hurricane. This doesn’t even count the potential for development in the Gulf of Mexico. So, 1998 still seems like a good match.
But, it looks like the strong southwest winds, associated with the jetstream, didn’t start until later in September. We are already there. Also, the bulk of the September precipitation came with monsoonal flow early in the month. The end of the September and early October were dry. But, but the end of October, the winter storm pattern had started. Has the 2010 timeline shifted? Are we one month ahead of 1998? We have had almost 10 inches of rain since June at the airport.
I’m still not ready to forecast for the winter, but, the winter of 1998-1999 ended up fairly dry.
As you can see below in the water vapor satellite image, the dry southwesterly flow(orange band) is passing us just to the north. As a result, the big puff of moisture that soaked Tucson and Phoenix over the weekend didn’t quite make it to Flagstaff. We are still very humid and have typically chances for rain for most of the week ahead.
There are a couple tropical entities playing into this pattern. To the west of Baja California, there is a slowly spinning low pressure area. To the south of the Baja Peninsula, there is a Tropical Storm Frank, soon to be Hurricane Frank. The way I look at this is that the low to the west has squeezed the dry air to the north for now. If it persists, we should have typical 30-40% chances of rain for the next couple days.
As Frank moves north, it should bring more moisture. It doesn’t look like it will dry create a dry layer ahead of it. However, as with all tropical entities, it could go either way. I expect we will get a nice moisture boost from Frank.
Also, the 4th tropical storm of the season was named Danielle over the weekend.
Forecasts for this year have been for a fairly aggressive hurricane season, but so far it has been an average season. But, we are right at the point where the season gets going with fervor. By August 22, 2005, we were up to Tropical Storm Jose, the 10th named storm of that year. 2005 was the year of Katrina. This year we have made it up to Tropical Storm Colin.
And area of disturbed weather, tagged as Invest 95, is developing off the coast of West Africa. It is expected to continue to develop. Will it become Danielle, the next named storm of the year? Here is a very cool chart from WeatherStreet.com. It will have to be a very aggressive fall to hit the forecasts.
Just a brief update…Saturday and Sunday will see a return to rainy, thundery conditions. Enjoy. There will probably be a break in a few days. But, remember, tropical development can change things quickly.
This might take a couple posts to actually get through the whole picture. It seems like there are 2 dominate issues and maybe a couple minor issues that are going to guide our fall and winter.
I’m a big believer that hurricanes can effect our weather via two mechanisms. First, they can deliver moisture to across Mexico from the Gulf of Mexico and the Caribbean Sea to our doorstep. This can cause precipitation to amounts to be higher than average. Second, they can actually disrupt the tropical moisture flow and locations of dominant high pressure systems. They can actually draw the moisture from thousands of miles around, drying out Northern Arizona. One of the big contributors to hurricane formation is the water temperatures in the Caribbean and Gulf of Mexico. La Nina’s are typically more favorable for active hurricane seasons. El Nino’s tend to generate a strong flow in the opposite direction of the normal hurricane paths, preventing hurricane development.
This Atlantic Hurricane Season is forecasted to be fairly strong with 14-20 named storms and 8-12 hurricanes (Climate Predictionn Center Hurricane Outlook 8-5-2010). This outlook was just updated. Although the season has started slowly, August to October are the peak months. There is still time for a strong season.
So, La Nina and El Nino can alter weather patterns significantly. El Nino in the fall and winter usually means wetter conditions. Last winter, an El Nino episode provided us with nearly 6 feet of snow in one week. Currently, the Pacific Ocean is building a La Nina episode. It just recently started to develop and forecasts vary as to how deep it will be. When looking at La Nina’s as an input to the precipitation outcome for the August-October time frame, There have been 7 La Nina’s through these months in the last 25 years, 1985, 1988, 1995, 1998, 1999, 2000, 2007. It’s arguable that 2000 was not a La Nina, but I have included it because the region was cold and clearly met the La Nina definition (El Nino Sea Surface temperature anomaly <-0.5) on either side of August-October.
|Year||La Nina SST Anomaly|
In 1995 and 2007, the La Nina’s were just starting around the mid to late summer time period. For this year, the outlook for the August-October time frame is between -0.5 and about -1.25. Again, this could match either 1995 or 2007. Notice a theme here? Don’t get too bent on 1995 and 2007 being good predictors quite yet.
Another interesting sea surface temperature anomaly to track is the Pacific Decadal Oscillation. It’s a broader, longer term look at the Pacific and how it behaves. It has been negative for most of the last 3 years. With El Nino ending, it returned to negative in June. This is expected to last, and intensify for quite sometime. We can assume it will be negative for the next 6 months. How do the other years look?
1985 amd 1995 were both positive. But, 2007 and 1998 were negative.
Now, the hurricane picture in those La Nina years is interesting, too.
|Year||Atlantic Hurricanes||Atlantic Tropical Storms||Gulf Hurricanes||Gulf Tropical Storms|
Remember, 14-20 named storms and 8-12 hurricanes are in the outlook. In this chart, tropical storms are equivalent to named storms. 1995 continues to be a potential match for this year. 2007 falls short on the total number of hurricanes, but is in the zone for total named storms. 1998 and 2000 are in the zone as well. The numbers of Gulf Storms are higher in many of the earlier years. But, 2007 still had 4 named storms in the Gulf of Mexico.
Here is where the real conundrum kicks in. When you take all of this data and add Flagstaff’s August to October precipitation to the chart you get this:
|Year||Flagstaff Precipitation||La Nina SST Anomaly||PDO||Atlantic Hurricanes||Atlantic Tropical Storms||Gulf Hurricanes||Gulf Tropical Storms|
The average precipitation for the August to October time periods in all these La Nina years is 6.78 inches, with a standard deviation of 1.95 inches. This put 1995 and 1998 at opposite ends of the spectrum and outside one standard deviation of the average. The positive PDO in 1995 with a La Nina, and an active hurricane season seems to point to a dry period.
To me, this seems to me to indicate that 2007, and maybe 1998, could be the best analogs for this year. A couple caveats about 1998. La Nina started just a couple months earlier than this year. It also followed a strong El Nino, in fact the strongest.
So, I am going to pick 1998 as the analog year for my forecast. Which would mean that we should see greater than average precipitation(1984-2009 average is 7.61 inches) for these months. In 1998, Flagstaff received 3.32 inches in August, 4.76 in September and 2.96 in October. I think we will repeat a wetter than average trend similar to this, not 1995′s very dry trend or 2007 average trend.
But what about winter? La Nina means drier…or does it?