Jul 072014
 

To kickoff the monsoon season in fine form, the Flagstaff Airport received a record-breaking 1.89 inches of rain on July 4, 2014. I didn’t see it reported in the Arizona Daily Sun’s website.

RECORD EVENT REPORT
NATIONAL WEATHER SERVICE FLAGSTAFF, AZ
1239 AM MST SAT JUL 05 2014

...RECORD DAILY MAXIMUM RAINFALL SET AT FLAGSTAFF AZ AIRPORT...

 A RECORD RAINFALL OF 1.89 INCH(ES) WAS SET AT FLAGSTAFF AZ AIRPORT
YESTERDAY. THIS BREAKS THE OLD RECORD OF 1.85 SET IN 1986.

More is on the way. Considering that the airport’s normal is 2.61 inches, rainfall for this month should not find it terribly hard to hit normal. There are some dry time periods over the horizon. Also, not everyplace received that much rain. Here is the rain totals for the month so far as independently reported to Rainlog.org at the University of Arizona. The monsoon season has had a healthy start.

Month to date rainfall for the Flagstaff area. July 7, 2014. (Source rainlog.org

Month to date rainfall for the Flagstaff area. July 7, 2014. (Source rainlog.org)

 Posted by at 6:40 am
Jul 032014
 

Dew point temperatures across Arizona will move higher over the next few days. This means more widespread thunder showers across the area. A friend of mine, TB, was mentioning his plans to hike around one of the creek beds near Sedona for the 4th of July. Flash flooding is a serious issue in the desert. Here are some flash flooding safety rules from the National Weather Service (in Ohio?):

  1. In hilly terrain, flash floods can strike with little or no advance warning. Distant rain may be channeled into gullies and ravines, turning a quiet stream into a rampaging torrent in minutes. Never camp on low ground next to streams since a flash flood can catch you while you’re asleep.
  2. Do not cross flowing stream on foot where water is above your ankles.
  3. If you are driving, don’t try to cross water-filled areas of unknown depths. If your vehicle stalls, abandon it immediately and go to higher ground. Rapidly rising water may sweep the vehicle and its occupants away. Many deaths have been caused by attempts to move stalled vehicles.
  4. Be especially cautious at night. It’s harder to recognize water danger then.
  5. Don’t try to out race a flood on foot. If you see or hear it coming, move to higher ground immediately.
  6. Be familiar with the land features where you live, work, and play. It may be in a low area , near a drainage ditch or small stream, or below a dam. Be prepared!
  7. Stay tuned to NOAA Weather Radio for the latest statements, watches and warnings concerning heavy rain and flash flooding in your area, report it to the National Weather Service.

I’m bugged by the fact that a quick search for “flash flood” on the NWS Flagstaff website didn’t turn up a document like this. Something that isn’t stressed in this list that is very important is that the storm can be far away and cause a flash flood where you are. Be aware of the weather upstream from your location. A small creek bed can be the sole drainage for hundreds of thousands of acres. If you are in a canyon, you may not be able to even see the storm. They do have a good webpage set up for monitoring the area around the Slide Fire.

Here is the North American Mesoscale precipitation model outlook through midday on Sunday.

Total precipitation from July 3 to July 6, 2014 from the North American Mesoscale Model at the Climate Prediction Center.

Total precipitation from July 3 to July 6, 2014 from the North American Mesoscale Model at the Climate Prediction Center.

 Posted by at 6:50 am
Jun 262014
 

The 8-14 day outlooks continue to look wet. Thursday, the 6-10 Day outlook from the Climate Prediction Center looks wet, too. This 6-10 day outlook includes July 2-8. The signs are good for a change to the monsoonal flow next week.

8-14 day precipitation outlook from the Climate Prediction Center, June 26, 2014.

8-14 day precipitation outlook from the Climate Prediction Center, June 26, 2014.

6-10 day precipitation outlook from the Climate Prediction Center, June 26, 2014

6-10 day precipitation outlook from the Climate Prediction Center, June 26, 2014

 

 Posted by at 1:08 pm

Wind forecast fades

 Monsoon  Comments Off
Jun 252014
 

I think the winds have taken a bit longer than usual to fade so that the monsoonal flow could begin. The winds have been strong and out of the west to southwest. Finally, the wind outlook shows the strength dropping through this weekend and swinging around to the south to southeast by early next week. Here is a graph from Wunderground.com showing the decrease in wind speed.

7-day graphical weather forecast from Wunderground.com.

7-day graphical weather forecast from Wunderground.com.

This next image is from this morning’s 10-meter wind outlook from the GFS model at the Climate Prediction Center. The forecasted wind direction is from the southeast.

10-meter wind and precipitation outlook for Monday afternoon, June 30, 2014 from the Climate Prediction Center.

10-meter wind and precipitation outlook for Monday afternoon, June 30, 2014 from the Climate Prediction Center.

 

 Posted by at 12:06 pm
Jun 242014
 

Well, the Climate Prediction Center has made a major shift in its 8-14 day precipitation outlook. Yesterday, most of Arizona moved into the above average precipitation zone for the 8-14 day period.  This period starts on July 2. This is very positive news of a wet and timely start to the monsoon season.

8-14 day precipitation outlook from the Climate Prediction Center (June 24, 2014)

8-14 day precipitation outlook from the Climate Prediction Center (June 24, 2014)

 

On June 23, 2014 the outlook had Arizona in the normal zone. This time of year, normal can mean wet or dry. On June 19, 2014, the outlook was for drier than normal conditions.

8-14 day precipitation outlook from the Climate Prediction Center.

8-14 day precipitation outlook from the Climate Prediction Center (June 23, 2014)

814prcp.20140619.fcst

8-14 day precipitation outlook from the Climate Prediction Center. (June 19, 2014)

 Posted by at 5:55 pm
Jun 192014
 

The good news is that most of Northern Arizona remains in the above average precipitation zone for the summer. Still, I don’t believe El NiƱo is the link. There are a combination of factors. The Climate Prediction Center issued a new 3-month outlook last week.

20140619-200139-72099503.jpg

The bad news is that the winds may not leave for another two weeks. The winds we have experienced lately are due to the jet stream moving far to the south. It would have been a blessing in the winter. But now, it delays the monsoon season.

 Posted by at 11:09 am
Jun 112014
 

The Arizona Daily Sun published this article over the weekend: Forecasters: Wet Summer and Winter likely in Flagstaff. This article hints at El Nino as the cause for both extra rainfall this summer and more snow next winter. About a month ago I started to look into El Nino’s effects on Flagstaff’s summer precipitation. My hypothesis was that El Nino actually lowered rainfall amounts in the summer.

Digging into the data since 1950, there really isn’t much difference between the over all normal for 1950-2010 and any of the El Nino averages based on the strength of the El Nino. There are huge swings in the summer (June-September) rainfall amounts. Just to make the point, The El Ninos of 1957 and 1982 are both strong. They produce 4.81 and 13.42 inches of rainfall. The El Ninos of 1986 and 1991 are both moderate strength. They produced 20.64 and 3.53 inches of rainfall. The weak ones are all around 7-8 inches of rain. It looks like anything goes with El Nino Summers.

There is more than just El Nino driving the events for the year. The Climate Prediction Center still has Flagstaff in the above average rainfall zone for the summer. They should have an updated model later this week.

On a side note, I noticed last night that AccuWeather.com had a thunderstorm in the long-range outlook for Flagstaff on June 24. It’s gone this morning.

June July August September Total
El Nino average 0.41 2.33 3.02 2.11 7.87
1950-2010 average 0.43 2.4 2.89 2.12 7.84
Strong El Nino Average 0.86 1.78 2.37 3.22 8.22
Moderate El Nino Average 0.28 2.59 3.38 1.72 7.97
Weak El Nino Average 0.15 2.42 3.05 1.61 7.23
1950-2010 average 7.7
 Posted by at 7:01 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.