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Weather in Boulder Creek, California
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Long-term Forecast

Three month outlooks for temperature and precipitation from the National Weather Service. Click on one of the two maps to see a larger version of weather trend for the next 90 days.


Temperature Outlook

Precipitation Outlook

For more long term outlooks see NWS' Climate Prediction Center.

I find that this is the fastest way to get a feel for the weather forecast beyond the typically reliable 5 day forecast, usually for the next 10 days. Check out the GFSx precipitation plot below to see what the GFS model is predicting beyong 5 days. Usually reliable especially for up to 5 days.

GFSx Sea Level Pressure and Precipitation Plot

Unisys Weather Forecast Model
This viewer contains contour plots from the Medium Range Forecast (GFSx) model. The GFSx (Global Forecast System) model output runs from observed data, every 12 hours to 10 days. These plots are updated once a day at around 10 AM EST based on the 00Z model run. downloads the graphic files everyday at 8 AM Pacific Time and uploads them to this site. What is useful, is that they can give an idea of weather conditions out to ten days. Granted, weather certainty decreases as the forecast model is further from today. All times are in Zulu Time or UTC, Universal Time Coordinate, which is 8 hours behind or UTC-8:00 (UTC-7:00 during PDT) Pacific time.

The above viewer allows one to view the sea level pressure and precipitation forecast chart includes three parameters: sea level pressure (cyan lines - hPa - Hector Pascals), 1000-500mb thickness (brown dotted lines, 5100, 5400, 57 solid lines) and quantitative precipitation (color contours). The cyan blue letter "H" represents high pressure centers which typically force and guide low pressure systems (storms if high in water vapor). High pressure systems typically occur off the coast of California and frequently prevent storm systems from landing.  The cyan letter "L" represents low pressure systems.
Sea Level Pressure
The sea level pressure field will detail the location and strength of high and low pressure systems as well as locate warm, cold and stationary fronts. The pressure contours or isobars are drawn every 4 millibars. Cold fronts generally follow the pressure trough flowing south and west from the low pressure system. Warm fronts can be located at times as pressure troughs going east out of a low but are generally hard to find. Surface winds are related to the packing of the pressure contours (isobars). The tighter the packing, the stronger the winds are.
Quantitative Precipitation Field
The quantitative precipitation field shows estimated 12 hour precipitation (liquid equivalent) for the 12 hour period prior to the valid time. For example a 12 hour precipitation field valid 12Z THU 11 NOV 93 would show 12 hour accumulated precipitation from 00Z THU to 12Z THU.

In addition, the precipitation forecast can be used to estimate snow fall. A general 10 to 1 ratio can be used for snowfall based on the liquid equivalent shown in this chart. Using the 850 chart freezing line to determine whether the precipitation is snow or not, you take the precipitation total at a location and multiply it by 10 to get potential snowfall.
1000-500 mb Thickness Field
Thickness lines are drawn in dotted brown at a 60 m interval. The 5100, 5400, and 5700 m lines are solid. This represents the thickness in meters between the 500 mb pressure surface and the 1000 mb surface. This is directly related to mean layer temperature and is often used to determine precipitation type. The 5400 thickness line is often referred to as the rain/snow line. Also, it is also known that surface pressure systems tend to move along thickness lines.
Note: The above descriptions from Unisys Weather: Forecast Model Details.

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Revised: 11 Jan 2009 10:59 -0800 GMT (Pacific)