Tuesday, April 24, 2018

Remarkably Good and Bad Snowpacks at Your Doorstep

We're now deep in April and near the time of maximum upper-elevation snowpack in the interior western United States.  The contrast in snowpack characteristics from north to south through our region could not be more striking.  If we look at SNOTEL stations at elevations at or above 8000 feet, there are many in Nevada, Utah, and southwest Colorado that have already lost their snowcover.  In contrast, to the north, there are some in the Greater Yellowstone area with more than 100 inches.  The maximum is at the Fisher Creek Snotel, which is just north of Cooke City, Montana. 

Snowpack water equivalent tells a pretty similar tale.  There's a total loss of snowcover at many sites in Nevada, Utah, and southwest Colorado.  The snowpack is phat to the north.   Sites above 50 inches of water are Fisher Creek noted previously and Grand Targhee in the Tetons.  Northern Colorado and south-central Wyoming have some decent numbers as well, including the Tower and Medicine Bow Snotels, both at 10,500 feet, with over 40 inches. 

We can also identify stations that are at their all-time lowest and highest snowpack water equivalents in the period of record.  This focuses on sites with at least 20 years of data.  Sites at record low snowpack can be found in the Ruby Mountains of Nevada, the southern Wasatch, the plateaus of southern and central Utah, the southern Wind River Range, and the mountains of southwest Colorado.  In contrast, sites at all-time highs can be found in the Dear Lodge Mountains of southwest Montana, the Absaroka Range of Montana and Wyoming, and the Big Horn Mountains of Wyoming. 

Finally, we can look at the percentile rank for these sites, with 50 indicating that the site is right in the middle of past years, values above 75 indicating that it is in the top 25% of past years, and values less than 25 indicating that it is in the bottom 25% of past years.  The contrast in snowpack as one moves northward couldn't be more striking, especially in the Wyoming and Wind River Ranges where one moves from a snowpack that is near or below median to solidly above median as one moves northward. 

It is not uncommon for the southwest to be dry when the northwest is wet (and vice versa), a pattern sometimes described as a precipitation dipole.  This dipole is in part related to ENSO, with La Nina favoring dry years and El Nino favoring west years in the southwest.  However, the contrast this year is especially abrupt and striking. 

If you are a skier, the dwindling Wasatch snowpack may be a bit depressing, especially as it becomes increasingly snirty this week.  On the other hand, you are not far from a remarkably deep snowpack.  Perhaps you should be thinking about a road trip. 

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