Snow (or lack thereof)

NoBos vs. SoBos

Many people have asked me why so many people hike the PCT northbound . The main reason is because of the timing of the snowpack and snowmelt. The springtime gives northbound hikers (NoBos) the best chance at finding creeks in Southern California from the snowmelt in the San Gabriel and San Bernardino mountains. It also allows enough time for the big snowpack in the Sierras to melt down a bit. Southbound hikers (SoBos) meet challenges with the snowpack if they start too early in the Cascades up in Washington and then must deal with dry conditions down in Southern California in the fall (however plenty of hikers have completed southbound trips).

Kennedy Meadows Date

One of the key dates northbound hikers traditionally plan around is June 15th. This is the average date at which snow conditions become manageable in the Sierra Nevada mountains. Thru-hikers will plan to leave Kennedy Meadows, one of the last major resupplies before for the Sierras, around June 15th. However this date can change based on the snowpack. Wilderness Press' Data Book offers the following equation to estimate when you should schedule leaving from Kennedy Meadows:

Kennedy Meadows Day = June 1 + (snow depth at Bighorn Plateau April 1st/3.5) days

Bighorn Plateau is one of the earlier peaks in Kings Canyon National Park the PCT travels by. This equation uses the assumption that in June the snowpack will melt down by roughly 3.5 inches a day.

Snow Depths

You can look up snow depths for each year at California's Snow Course website. (Bighorn Plateau is snow course number 250) Looking at the data, one can clearly see that snow conditions are very different from last year and relatively variable in general. Last year was one of the largest snowpacks in the history of the trail, as any 2011 hiker would tell you. Us 2012 thru hikers will have a much different experience with a rather dry winter. This year at the end of March Bighorn reports 20.6" of snow while last year it was at 106.0"! This is quite a jump when you consider most years average around 60" at the end of March.

Year	2002	2003	2004	2005	2006	2007	2008	2009	2010	2011	2012
Bighorn Plateau Depth (in)	65.3	49.1	41.1	90.1	53.0	20.0	65.0	59.3	62.5	106.0	20.6

If you plug in these depths to the above equation in 2012 hikers could plan on leaving Kennedy Meadows as early as June 7th. My schedule doesn't put me in Kennedy Meadows until June 20th so there shouldn't be too much snow for me to worry about at all.

Why No Snow?

While I wish there was a simple answer to this question there simply isn't one. This highlights the difficulties in modelling climate patterns and predicting weather events. While we are seeing the effect of climate change around the globe, this drop in snowfall should not be taken as evidence of climate change (and too many people confuse these annually difference with climate trends). Such a signification drop from one year to the next is not a direct consequence of a warming planet, although there is evidence linking climate change to increased variability in weather patterns and quasiperiodic climate trends. If you want to take a look at some interesting data from climate models of California check out this cool tool from Cal-Adapt.

One climatic pattern that largely governs precipitation in California is El Nino, more formally referred to as the El Nino/La Nina-Southern Oscillation or ENSO. ENSO is driven by an interplay between wind currents and ocean currents. It varies between periods with a warm layer of surface water off the coast of California (El Nino) and periods with colder surface waters (La Nina).

El Nino's impact on weather conditions varies depending on your location on the PCT. In the Pacific Northwest, El Nino can produce warmer dryer winters, while in Southern California it will likely produce significantly wetter winters. La Nina largely has the opposite effect producing significant precipitation in Northern California and the Pacific Northwest and reduced winter precipitation in Southern California. Many people note these differences in trends based on location, especially skiers who may see some ski resorts prosper or fail depending on ENSO.

The big snowfalls last year in Northern California were largely explained by strong La Nina conditions. However here is where theories and trends don't always hold, because this winter has also experienced strong La Nina conditions and the snow hasn't fallen. So again sorry there isn't a simple answer to why the snow didn't come this year but I am more than excited to not have to post hole my way through huge snowpacks like hikers last year!