This is a lot to digest but you can just use the flood forecast pages if you like. The point of the other links is that, several days in advance of the flood forecasts, you can find out about conditions that could lead to flooding. Don’t use any of this as a basis to ignore official weather and flood forecasts, official flood information and warnings and your own good judgment and experience.
The order of the links below generally relates to the sequence of events that lead to flooding on the Garden Highway. Thus, weather that can lead to flooding and is beyond the 7 day range of official Weather Service Forecasts may show up first in the forecast discussions, then the forecasts will start to predict storms, and then they show up on the satellite pictures, and then on the precipitation radar. Then you start monitoring the rainfall accumulations, river rises, reservoir releases and flood forecasts.
The reservoir release site at (13) below is probably the most immediate link for predicting river rises. A series of large storms sets the stage, but the river doesn’t seem to flood most yards until the reservoir releases are increased. The timing of rises along the Garden Highway after increased releases is dependent on how close the reservoir is. Shasta releases take several days to travel downstream to reach us. Oroville releases take about a day. Folsom releases are faster. Note that although the American River is downstream, rises on that river will “dam” the Sacramento River and cause it to rise upstream. When the gate broke on Folsom Dam several years ago, the level on the Sacramento River, 7 miles north of its confluence with the American, went up eight feet. There is usually a lag between when release increases are posted on this website and the official flood forecast is revised. You can get an earlier warning about possible rises on the river by monitoring this site. Whether releases are large enough to flood your yard depends on the size of the release, how much water is already in the river and your yard elevation.
1) Sacramento Technical Discussion.
Technical discussions are usually updated 4 times a day and are useful for discussing conflicting evidence about the weather forecast. So you hear about possibilities that don’t show up in the official forecast. The forecasters aren’t afraid to speculate and their personalities show through. There are lots of abbreviations used; "fropa" means frontal passage, for example.
2) San Francisco Technical Discussion.
Another technical discussion. Comparison of this one with Sacramento’s is illuminating because they sometimes reach different conclusions about the same storm.
3) National Weather Service San Francisco.
The mother of local weather pages. Many of the links below are from this page.
4) National Weather Service Sacramento.
Most info on this page is available on the SF page. Forecasts are generally updated every 12 hours.
5) Hawaii to West Coast Satellite Pictures.
There are dozens of satellite pictures available. This one shows the storms out to just west of Hawaii and is updated every 2-3 hours. The colors depict cloud top temperature - the more dynamic and stronger the storm, the higher and colder are the cloud tops.
6) Northern CA Radar
Updated at least every hour. Shows areas and intensity of precipitation in northern California and just off the coast. Also shown are the height of the cloud tops and the speed and direction in which they are moving.
7) Hourly rain totals.
From around the state, grouped by river basin, updated hourly and including cumulative totals for the last 1, 2, 3, 6, 12, and 24 hours. After monitoring this for a few storms, you will get a sense of how much rain is “normal” for different areas and how much is especially intense and potentially the cause of significant river rises.
8) Seasonal rainfall.
This SF Chronicle site appears to replicate NWS data but I haven’t found the NWS site that has seasonal rainfall. Not so important for flood forecasting and updated every day at 4:00 pm, it shows data for selected stations around CA with 24 hour totals, season to date, normal to date etc.
9) Major River and Stream Stages.
Selected gauging stations from around the state arranged by river basin, updated hourly and includes data for the past few hours. You can see what's happening on the smaller streams to get an idea of what will happen on the big ones. This page is good for following the progress of a crest down the Sac. River.
10) The Lower Sacramento River flood forecast.
Includes the river elevations at major gauges at the time of the forecast, is updated daily at around 8:00 AM and includes forecasts for the lower Sacramento River, Rio Vista, Clear Lake, Cache Creek and the lower American River. During floods and when reservoir releases are suddenly changed, the forecast will be revised more frequently:
11) The Upper Sacramento River flood forecast.
Contains info analogous to the lower sac forecast:
12) Reservoir Levels.
Updated daily to show the present levels and capacities of the reservoirs. If you click on the three letter link for any particular reservoir, you go to a page where you can get further reports about that reservoir. In this next page, if you click on “daily” you can find something called: “RESERVOIR, TOP CONSERV STORAGE.” This is the maximum level to which officials want the reservoir to be filled for the day you’re looking at it. This will be a lower level in the beginning of the winter, when the goal is to preserve reservoir space for accommodating future storms. Once the reservoir is filled to that level, more water will be released from the reservoir, which will cause the river to go up. So you can compare that maximum level with whatever the present level is and figure out if releases may soon be increased.
13) Scheduled reservoir releases.
Scheduled and past reservoir release quantities, updated as release changes occur. If you click on the "2 day" hyperlink on the page, you may not see some reservoirs because their releases have not changed within the last 2 days. One of the most useful sites because increased reservoir releases are usually a prerequisite to flooding. :
14) The Verona Gauging Station.
Updated hourly, lists data for the last few hours and can be queried for past data. The station is located on the Sacramento just downstream from the confluence with the Feather. You can also have data from the last day or so plotted on a graph. This is the station most relevant to the north end of the Garden Highway. Southern Garden Hwy folks may want to use the Sacramento Weir or I St. stations as a guide. Check the reading at Verona the next time water starts to come into your yard. Then you can monitor this webpage and the forecasts and have a fair idea if that forecast level will cause your yard to flood. Since most yards are not right at the gauging station, this is somewhat of an approximation. There are hundreds of other gauging stations around the state with hourly readings on the Net, accessible through the next webpage listed below, some of which may be more useful to you. If you click on the column heading "RVR STG", the data will be displayed graphically.
15) The CA Data Exchange Center Web Page.
A comprehensive flood and hydrology page run by the Department of Water Resources which has many of the pages listed above:
16) Madden Julian Oscillation.
This is the name of a 30-60 day weather cycle in the tropics that affects California weather. I am just starting to use this to consider what the weather might be a month and a half out, which would matter if you were considering a vacation during flood season. For background MJO info, go to http://www.cpc.ncep.noaa.gov/products/intraseasonal/intraseasonal_faq.html An analysis that depicts the actual MJO is at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_mjo_index/mjo_index.html You can see the periodic increases in convection that occur at our latitude – about 120 degrees west. Based on the background info, increased convection at 155 degrees east is associated with stronger storms in our area of California. If the MJO turns out to be a useful indicator for us amateurs, it would be one of the earliest first warnings of bad weather.
notes:
1) When you call up many of these pages, you will see an image which may be the last one conveyed to your computer by the website, rather than the most current version. Check the dates and times of the charts and pictures to make sure you have the latest. Click on "reload" to update old data.
2) Many of the sites use 24 hour Greenwich time - the radar image would be labeled 1845Z, for example. Until daylight savings time, subtract 8 hours from the Greenwich time to get local 24 hour time; during daylight savings time, subtract 7 hours.
3) The operators of these web pages occasionally change addresses so some of these may become outdated by next year.
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