||Published Tuesday, February 29, 2000 in the San
Jose Mercury News
Weather forecasting better than 20 years ago
BY JAN NULL
Special to the Mercury News
Q. A few people recently have written letters to the Mercury
News complaining about the current deplorable state of weather forecasting as compared to
20 years ago. Are they right? Was weather forecasting better then? Dinesh Desai -
A. I couldn't disagree more. Twenty years ago, the reliability of a
five-day forecast was only slightly better than 50 percent.
Now, five-day forecasts are correct about 80 percent of the time. I believe the issue is
more a matter of people's perceptions of the forecasts.
In the 27 years I have been forecasting weather in the Bay Area, I have found that people
often hear only what they want to hear. Or they hear a radio disc jockey paraphrase a
forecast into something totally different than the original. These problems are
exacerbated by the plethora of weather sources now available, to the point where
people often don't know exactly where they got a particular forecast.
This past weekend was a prime example. One forecast Thursday called for the possibility of
as much as 3 to 5 inches of rain ``in the mountains of Sonoma and Napa counties.''
However, all day Friday and Saturday, I heard numerous reports in the media talking about
the entire Bay Area getting drenched by 3 to 5 inches of rain. The North Bay mountains did
get about 3 inches of rain, but certainly the entire region didn't.
The bottom line is that forecasts have gotten so consistently good that the only ones now
remembered are those that were wrong.
Q. How far north has a hurricane ever traveled in the United
States? Clark Hagman - Menlo Park
A. Hurricanes have moved along the East Coast as far north as Maine, or
to a latitude of about 45 degrees north. This is about the same latitude as Portland,
Ore., but there is a key difference between the east and west coasts.
On the East Coast, the hurricanes derive much of their strength from the 75- to 85-degree
waters of the northward-flowing Gulf Stream. But here along the West Coast, the ocean
currents come from the north, with 55- to 65-degree waters, a condition not favorable for
The closest a hurricane came to California was in 1939 when a tropical storm struck the
Long Beach area with winds of 40 to
60 mph. This storm (they were not given names in 1939) was responsible for 45 deaths and
As hurricanes in the eastern Pacific dissipate, their moisture may spread northward into
California and result in thunderstorms, heavy rain and flooding. Flooding from Hurricane
Kathleen in September 1976 caused $65 million in damage to California's agriculture.
Q. I windsurf in the San Francisco Bay from April until
October if there is sufficient wind. The preferred wind is 15 mph or
greater from the northwest. What is the best source for getting this information? Reports
every 15 to 20 minutes would
be very helpful. Carl Grame - Los Altos
A. My favorite Web source for San Francisco Bay wind data is a very
nice wind flow map produced by the U.S. Geological
Survey with data from the National Weather Service and other agencies
(http://sfports.wr.usgs.gov/wind/). Unfortunately, there is no single publicly
accessible source that has a comprehensive listing of wind reporting sites in the bay, and
what data is available is updated only about once an hour. Check the following Web sites:
There are also a number of subscriber-based wind reporting services that will even page
you when the wind reaches a certain speed. Your best source of information would be local
windsurfing organizations and marinas.
Q. I am looking for a place to retire and wonder if there is a
source of detailed weather information. Annual graphs of highs
and lows, humidity, days of sun, etc., would be extremely helpful. Gene Hardin -
A. Good luck. There have been numerous efforts made to find the
most ``livable'' places, but a person's climate preference
is a very subjective choice. Additionally these choices are tempered by the activities we
enjoy, our health and, of course, what our significant other wants in the way of weather.
Many libraries will have either ``The Weather Almanac'' (USA Today, 1995) or ``Climates of
the World'' (NOAA, 1991), which have climate data for many cities. I have also put
together data for about 300 United States cities online (http://ggweather.com/ccd/). Other
excellent sources of climate averages on the web include www.weatherbase.com
and www.cdc.noaa.gov/USclimate/ .
Q. Have heard on occasion that San Jose is in a ``rain shadow.'' What
does it mean? Paul McKiernan - San Jose
A. The Santa Clara Valley is indeed in a ``rain shadow.'' Heavy
rain falls in the coast range and Santa Cruz Mountains to the
west, but places like San Jose get considerably lighter amounts.
That's because the mountains force rain-laden storm clouds to move higher into the
atmosphere, wringing out much of the rain. By the time these clouds cross over the
mountains to reach the valleys to the east, some of the rain-forming moisture has been
There also is sinking air on the east side of the mountains, another detriment to rainfall
in the valley. As a result, the Santa Cruz Mountains often get three times as much rain as
the Santa Clara Valley. Annual average rainfall is 48 inches at Ben Lomond but just 14.5
inches at San Jose.
Jan Null, founder of Golden Gate Weather Services and Director of M eteorology for
Planetweather.com, is a retired lead forecaster with the National Weather Service. Send
questions to him c/o WeatherCorner, San Jose Mercury News, 750 Ridder Park Drive, San
Jose, Calif., 95190. You also can telephone and fax questions at (510) 657-2246 or e-mail
to email@example.com. firstname.lastname@example.org.