Thursday, May 17, 2012

Peak flow near?

Picking the peak flow of any river is tricky business.  It's a lot like betting on a horse race or buying a lottery ticket.  Sometimes you get lucky and look real smart.  Most of the time, you're way off base and look real dumb.  In spite of the risks of looking stupid, we continue to attempt to "peg the peak" on various rivers each year.  It's fun.

We think the Salmon River at Yankee Fork is nearing its peak flow.  In the blog post below, we already went out on a limb and called for the peak on May 20th.  That's only 3 days away.  It's possible the river just might peak before this coming Sunday.

The Galena Summit snowpack peaked on March 18 at a depth of 83 inches.  The water contained inside the snow peaked at 22.5 inches the first week in April.  As of May 17th, we're looking at a mere 13 inches of snow remaining with just 5.3 inches of water.  Rate of loss is about 2-4 inches per day for the snow and 1.0-1.7 inches for the water inside the snow.  As of today, only 15% of the original snowpack remains whereas 23% of the snow water equivalent remains.  If yesterday's rate of water loss were to continue the snow water would be gone in 3-4 days.  Ditto the snow itself.  Chances are that's not going to happen.

Here is a snippet from the morning Pocatello NWS Forecast Discussion:


 DEEPER MOISTURE AVAILABLE FOR HIGHER AMOUNTS OF PRECIPITATION WILL REMAIN IN PLACE INTO FRIDAY...WITH PORTIONS OF THE CENTRAL AND EASTERN MOUNTAINS SEEING POTENTIAL TOTALS IN EXCESS OF 0.25 INCHES. IT STILL LOOKS
LIKE SNOW LEVELS WILL DROP TO THE 8000-9000FT RANGE...ALLOWING FOR AN INCH OR TWO OF VERY WET SNOW TO ACCUMULATE AT OR ABOVE THOSE ELEVATIONS.


Yesterday's high temp in Stanley was 73 degrees, 15 degrees above normal and almost 30 degrees warmer that last year's unseasonably cool spring.  Today's high will barely get into the 60's and then a storm will hit the mountains with the snow level dropping as low as 8,000 feet.  That's right smack dab where the remaining snowpack is sitting--at or above 8,000 feet.  So, basically what that does is shot down the rapid rate of loss in the snow and its water content.  It will be like someone turned off a spigot.  POOF, gone.  The river should drop sharply within the next few days.  Meanwhile, the storm will not have deposited enough snow or water to create any kind of rapid future rise.  When the next warm spell ends, the river will already be much lower than today's readings.  The next warm phase and resulting melt of the remaining snow will be too little to bring a secondary peak that could exceed the one that will be in place within the next 12-72 hours.

So, there you have it--The Salmon River's 2012 peak flow is happening right now.  The thing to keep an eye on is the actual gage height.  You can find that by clicking on "Table" instead of "Graph."  As of right now it's 7.75 feet and "fluttering" at this level.  It's struggling to get much higher that that.  It's going to be hard to imagine any kind of a huge surge taking it much higher than the current level.

However, as they say, "Stay Tuned!"

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