May 302010
 

A recent post, (Western Snowpack is 137% of Normal) at Watt’s Up With That? (www.wattsupwiththat.com) raised questions in my mind about the current and future water level for Lake Powell. The post covered current snowpack in the west and the changing levels of Lake Powell. While Arizona had a very wet winter, 12 feet of snow fell in Flagstaff, the areas that contribute to Lake Powell’s inflow did not have great years. Also, since the snow stopped falling in earnest, Flagstaff has seen a significant dry spell, with lots of wind. So, how to dissect all of this?

First, let’s take a look at the season’s snowpack. Here is a chart that tells an interesting story and was shown at Watts Up With That.

Western US Snowpack 5-25-2010

Western US Snowpack 5-25-2010

The overall average is impressively positive. But, Colorado and Utah are both below average. While not as dry as some recent Flagstaff winters have been, Utah and Colorado are both below normal. For much of last winter, the snowpack above Lake Powell has been below normal. Today, the snowpack is reported as being 68% of average for this date. The total precipitation is reported as 88% of average. (Reference: http://lakepowell.water-data.com/) Again, 88% of normal isn’t terrible when considering some recent years. In 2002, the lake level pretty much fell all spring and summer.

Lake Powell Snowpack - 2007 to 2010

Lake Powell Snowpack - 2007 to 2010

This last winter has been consistent. The percent of normal snowpack has remained a 70-90% band for most of the winter. Notice how early warmth of 2007 and 2009 caused the snowpack to diminish rapidly. There is more to this story. Take a look at the departure from normal daily mean temperatures for late April and early May in Grand Junction, Colorado.

Departure from Normal Daily Mean Temperatures Late April to Early May 2010, Grand Junction, Colorado

Departure from Normal Daily Mean Temperatures Late April to Early May 2010, Grand Junction, Colorado

Like most of the Southwest, several cool storms pushed May temperatures below normal. This helps prevent the snow melt from accelerating. It also put a hiccup in the inflow rates for Lake Powell. For a while in May it looked like the spring run-off had ended early.

Lake Powell Water Levels 2010

Lake Powell Water Levels 2010

Early May water level measurements show a small plateau. Still, given the low snowpack levels for the year, this years increase in level is going to be as noticeable as the massive recoveries of 2008 and 2009. Thankfully, the water level stayed high enough this year to keep the Castle Rock cut-off open through the winter. This saves a considerable amount of gas by not having to go around to the south.

Lake Powell Water Levels - 2006-2010

Lake Powell Water Levels - 2006-2010

The post at Watts Up With That? goes on to discuss the overall lower precipitation rates in the West since last October. Yes, lower than average. While we had record breaking storms in December and January, many of the other months in the last year have been below average. Remember, the summer of 2009 was nearly a summer without a monsoon season. But, most of the West has been cooler than normal as well.

So, where will Lake Powell end up this year? I think we will see a later peak that 2007 with an increase of 15-20 feet. This will put the lake in the 3635 foot level (my official guess). Below last year and about the same as 2008. The cool temperatures have delayed the spring melt for a while. The absence of heavy precipitation late in the season prevented a big boost to snowpack from being realized. Still, the snowpack remaining is much higher than the 2007 and 2009. So, there is still time to see the water arrive at the lake.

At Wayne’s Words website (www.wayneswords.com), Wayne Gustaveson run an annual contest to guess Lake Powell’s peak water level. A survey of the guess’s posted there shows an average guess of ~3642 feet and a median guess of ~3643 feet. Knowing that none of us is as smart of all of us, I wouldn’t be surprised to see the peak level to come in at 3642-3643 feet. Wayne keeps tons of great information at his site. I highly recommend visiting it before you go to Lake Powell.

Stu

 Posted by at 4:19 am

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