Aug 172014
 

In my last post, I pointed out that a drier period was ahead. What I had meant, and what the models foretold, was no rain for a week or so. That has not been the case. Thursday evening, a storm moved across the west side of Flagstaff dumping heavy rain across the area. Friday evening a storm hit central Flagstaff. I got about 1/3 of an inch of rain. I got more rain on Saturday, a mere 0.03 inches. This is drier than earlier in the week when I received over an inch.

This dry trend will continue for the next few days with a 30-60% chance of rain each day through Thursday. I think that in wet years, the forecast models run on the dry side, especially at long lead times. In dry years, they run on the wet side. The result is that more is on the way for this week.

 Posted by at 10:16 pm
Aug 132014
 

It’s hard to believe since it rained all night last night, but another break in the action is ahead. The weekend might be a bit wet, but next week is looking mostly dry.

I think this is due to the repetitive formation of hurricanes off the coast of Central America. These storms keep forming and rolling off to the west. This pattern shifts the monsoonal flow. I haven’t checked the exact numbers for Flagstaff, but we probably surpassed the average precipitation total for August with this current storm.

 Posted by at 6:13 am
Jul 182014
 

This morning the Climate Prediction Center issued a new 90-day precipitation outlook. All of Arizona is in the above average precipitation zone.

Three-month precipitation outlook from the Climate Prediction Center.

Three-month precipitation outlook from the Climate Prediction Center.

 Posted by at 7:14 am
Jul 162014
 

Starting today, the dew point temperature is going to fall. By this weekend, our dew point temperature will be in the 20s. This is well below the damp 50+ dew point temperatures we need for good thunderstorm activity.  But, the moisture should build back into the region by early next week.

Below are the dew point outlooks for Friday night and midday Monday. Notice on Friday night that white covers Northern Arizona indicating dew points at or below 25 degrees F. By midday Monday, a knuckle of moist air moves into Northern Arizona bring the dewpoints back to the mid 40s. Hopefully, by Wednesday of next week, we may see a return of thunderstorm activity.

Dew point temperature outlook for Friday night. From the National Center for Atmospheric Research.

Dew point temperature outlook for Friday night 18 July 2014. From the National Center for Atmospheric Research.

Dew point temperature outlook for midday Monday, 21 July 2014. From the National Center for Atmospheric Research.

Dew point temperature outlook for midday Monday, 21 July 2014. From the National Center for Atmospheric Research.

 Posted by at 6:33 am
Jul 152014
 

Looking out 2 weeks, you might think so. Today is the last day in the current forecasts and outlooks when Northern Arizona can strongly expect rain. The winds are going to shift back to a southwesterly origin and bring dry air. Below are the 6-10 and 8-14 day outlooks. The Climate Prediction Center issues new 30 and 90-day outlooks on Thursday.

As a side note, it looks more and more like El Nino is going to fail before it is up and running. I get in to that detail later. However, this probably isn’t the driver behind our monsoon season.

6-10 day precipitation outlook from the Climate Prediction Center. (14 July 2014)

6-10 day precipitation outlook from the Climate Prediction Center. (14 July 2014)

8-14 day precipitation outlook from the Climate Prediction Center. (14 July 2014)

8-14 day precipitation outlook from the Climate Prediction Center. (14 July 2014)

 Posted by at 6:33 am
May 252014
 

With a fire at this time of year, it’s natural to look at the calendar and think about how long until monsoon season, and will it be a good one. The Climate Prediction Center has Flagstaff inside the above normal region for the June-August and the July-September 3-month precipitation outlooks(see below). The current June outlook has us at even chances for normal precipitation.

A particularly interesting part of the monsoon season is Eastern Pacific hurricanes and tropical storms. These can bring exceptional moisture to Arizona. Hurricane season for the Eastern Pacific start on May 15th. Hurricanes do not usually form in May in this region, but they can. If they do form, they usually wander around the coast of Southern Mexico or drift straight out to the west. This year, we have our first storm, Hurricane Amanda. The computer models show Amanda moving up the West Coast and bringing moisture to Arizona by late in the week. It is still 5-7 days out, but it could at least help keep our temperatures lower and out humidity higher for a while.

One last note: The Climate Prediction Center issued an El Nino watch. The current outlooks show a strengthening El Nino that could be quite strong for next year. My current question is whether this could derail our monsoon season.

3-Month precipitation outlook for July, August and September from the Climate Prediction Center.

3-Month precipitation outlook for July, August and September from the Climate Prediction Center.

3-month precipitation outlook from the Climate prediction Center for June, July and August.

3-month precipitation outlook from the Climate prediction Center for June, July and August.

 Posted by at 4:55 am
Sep 262013
 

A recent question I have heard frequently is “Since the monsoon season was so wet, does that mean we will have a snowy winter.” A few years ago, the National Weather Service in Flagstaff included a slide in their winter outlook presentation that showed no clear link between summer and winter precipitation. In general, given the mechanisms for out summer and winter weather patterns, they shouldn’t be linked.

I cover the summer monsoon pattern in detail on this link: Summer Monsoon Mechanics. In this season, a thermal low develops over the deep southwestern United States. Also, a high pressure system forms over the middle of the country. The anticyclonic and cyclonic flows around these systems drive flow from the south and southeast. This flow draws up moisture from the Gulf of Mexico and the west coast of Mexico. Since the jet stream remains far to the north, these systems can be fairly stable. The big disruption of the monsoon pattern usually comes from hurricanes in the Gulf of Mexico. Interestingly, this year’s hurricane season has been anemic with only 2 hurricanes forming in the Atlantic. The other very wet year, 1986, saw a season total of 4 hurricanes.

Summer Monsoon Season Pattern

Summer Monsoon Season Pattern

In our winter pattern, the jet stream drops farther to the south and drives strong storms from west to east. In winters with a El Nino in the equatorial Pacific, the jet stream can split in two. One jet remains to the south and carries storms across the southern tier of states. The moisture reservoirs for the winter pattern end up being different from the summer. One supply area is from a large area near the Hawaiian Islands. When this water is warmer than normal it can be a powerful moisture supply. This happened in December of 2010. The other moisture supply can be from the equatorial Pacific in El Nino years. Occasionally, in very cold years, the Pacific Ocean off the west coast of Mexico can be warmer than normal and provide limited moisture.