Thursday, January 5, 2012

January 1 Snow Surveys and the Iowa Caucus

January 1st is a very big day in forecasting across the Western United States. An army of snow surveyors sets out into the mountains to check how deep the snowpack is. In groups of two or more, they visit hundreds of sites from Arizona to Alaska. They go by snowshoes, skis, snowmobiles, snocats, helicopters, small planes and everything in between. This tradition has been going on for more than 100 years and will be repeated several times throughout the year.

Back in the 1940s, some snow surveyors were nuts enough to try and attach an airplane propeller to a snowmobile.  Definitely would not pass modern health and safety rules. 
January 1st is the first snowpack reading of the year (not just of the calendar year, but also what hydrologists call the "water year"). It is an early indicator of what is to come. The snow has months to accumulate throughout the winter so that it can melt in the spring and feed the rivers. If the season gets a slow start, it can be hard to catch up. Some have likened these mid-season "polls" of the snow to seeing how far ahead or behind someone is during the middle of a race.

Montana snow surveyors take a core sample last year.

Speaking of races, I am completely thrilled that this is an election year in the US. There are heaps of great analogies for forecasting and elections.

Next the surveyors weigh the tube and snow core.

For example, this January 1st snow survey is to summer water supplies as the Iowa Caucuses are to the US Presidential Election. For our overseas readers, the elections have a couple phases:

First comes the caucuses to nominate a candidate from each party (Democrats and Republicans). Then the parties each pick one candidate (in August). Then the parties run against each other in the final election (in November). Right now it is so many months ahead, how can anyone possibly know who the eventual winner will be? Similarly, the runoff season is many months away- how can January's snow tell what June or July's runoff is going to be?

According to historical caucus results, unless a candidate runs unopposed, winning the Iowa Caucus gives you about a 54% chance of being the party's candidate. If this sounds like a coin-flip, consider that typically the winner has to beat three to five other candidates. For example, nobody that ever came in last place in the Iowa Caucus ever won the election.

Remember this guy? Bill Clinton only got 3% of the Iowa Caucus vote but still won the election.  Long shots occasionally happen they but aren't often the best bet. 
The results of the January 2012 snow survey will appear on the web (after the agency resolves a security concern- they say check back after January 6). In the meantime, there are automated measurements being transmitted from remote sites already and here is the main snow data portal. A common text-based report that people like is the snow update report. Personally, I find maps easier to read than tables and when I was with the agency, I helped develop a snow GIS map area.

Two important maps are the precipitation "Water year to date % of normal" map and...

Precipitation map, click to enlarge
the snowpack "Current % of normal" map.
Snow map, click to enlarge
The obvious thing to see is that California, Nevada, Oregon and parts of Utah are bathed in red, suggesting that they're getting a very slow start to the snow accumulation season. Arizona and New Mexico in the south are blue, showing a healthy snowpack. There are other maps on those above pages where you can find out that, for example, Lake Tahoe in eastern California has the least snow that it has ever had for this time of year. In the snowpack race, California is running very far behind.

That's nice, knowing the snow and all, but what exactly does it mean for summer runoff? Stay tuned for the runoff forecasts themselves, expected in a few days...

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