A Fan’s Notes on Water Supply

When you first move to California from someplace where rain is just a normal part of life all year round, some of the information that shows up on the newspaper weather page seems a little odd. I'm thinking especially of the rainfall totals, calculated between July 1 and June 30, and of the reservoir and snow-depth reports. Yeah, it's vaguely comforting to know some big lake somewhere is nearly full of water, and it's troubling when it's not. The snow report makes sense when you, the auslander, learn that a lot of the water that will wind up in the reservoirs starts out as vast quantities of white stuff in the higher reaches of the Sierra Nevada. The snow and water tables in the paper generally include references  to the total for a year ago and to what's "normal" for the date. If you spend any time at all on the weather page, you develop a sort of rooting interest. Wet years with more than 100 percent of the expected rain and snow can make you feel like the home team is playoff bound. Dry years resemble those lost seasons when all the supposed stars flop and nothing quite goes right.

If the precipitation and snowfall reports are the daily standings of the water year, then meteorologists  serve as both play-by-play announcers and analysts. If you're a serious fan and want to go beyond the entertainment offered by most TV weather presenters or the few vague words that make up most newspaper and online forecasts, then you have to go to the meteorological analyses published online by government weather services. Even in that world, there are circles within circles: for the interested generalist, there's the Area Forecast Discussion posted several times daily by most National Weather Service offices (for example, here's the AFD from the Monterey, California office). Informing those discussions are weather models–vastly complex, supercomputed pictures of the weather many days into the future; the true weather fanatic learns at least the rudiments of the models, their individual peculiarities, and what they might mean in terms of observable local weather.

Me, I haven't pushed the geek level much. I'm pondering the meaning of terms like "500mb heights" and  "pressure surfaces" but don't employ them in polite company or even bar-room conversation. However, my interest is real. We're nearing a key date in our water year–the California Department of Water Resources will take its first formal snow measurements of the season in a couple of days. Fans will be watching closely because frankly our 2009-2010 water year hasn't gotten off to a great start; while most reservoirs are a little fuller than they were a year ago, most are also well under average levels.

Now, while I'm waiting for the pre-measurement festivities to begin, I'm consulting the oracles of the sport. Among my newer winter weather reading is the California-Nevada River Forecast Center's daily "Hydrometeorological Discussion." Issued at 9:30 a.m. every morning, it summarizes rainfall and snowfall for the last 24 hours, then reviews what the weather models are saying about incoming storms for the next three days. Whereas the Area Forecast Discussion focuses on conditions in the geographic districts they cover, the CNRFC discussion looks at conditions in watersheds and river drainages. If you live in California and you're preoccupied with  water supply, the rain falling in the mountains above Lakes Shasta and Oroville, the state's two biggest reservoirs, probably means a lot more than whatever happens to fall on your neighborhood–where there's no place to store all the water that's coming down.

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