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For this Hydrology project, we chose a gage at the headwaters of the Sacramento
River at Mt. Shasta in Northern California. Our gage had minimal regulation and a long record dating back to 1959. Monthly streamflow values were obtained from the U.S.G.S. website and monthly precipitation values from the U.S. climate division dataset on the
Climate Diagnostics Center website.
Our site was located in a division 2 climate division in California and data was obtained based on this characteristic. Monthly streamflow data indicates a snowmelt driven watershed, as the peal flow was in the spring. Monthly precipitation data shows this same trend with a peak in precipitation during the winter months, showing that it is definitely a snowmelt driven watershed.
Seasonal streamflow was calculated for the months of March through May when there was a significant peak in streamflow at the gage. Based on these seasonal streamflow data for the 40 year period, the four highest and lowest seasonal streamflow years were chosen for composite pattern analysis. For our composite analysis we chose the season of October to March since it is a snowmelt driven watershed. Based on these four highest and lowest seasonal flow years, a composite pattern of geopotential height at
500mb, vector winds, and SST were all created. The resulting plots can be seen in the following figures.
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The plot on the left corresponds to geopotential height during high flow years and the left is during low flow years. The left plot shows a cell of low geopotential height (or low pressure) which occurs during high flow years. The right plot shows a cell of high pressure in the Pacific Ocean which tells us that it is going to be a low flow year.

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The plot on the left is vector winds during high flow years and the right plot shows vector winds during low flow years. For high flow years, the vector winds show counter clockwise rotation which corresponds to a low pressure system and high periods of rainfall. The opposite is shown during low flow years. Clockwise patterns correspond to a high pressure system and low flow years.
These two plots show the surface skin temperature (SST) for high flow years (left plot) and for low flow years (right plot). The left plot shows a warm region just off of the west of California which will lead to a seasonal high flow when coupled with northerly, counter clockwise vector winds. The right plot shows the opposite with a cold region in the Pacific which will not lead to precipitation, rather a low flow year.

This plot shows the seasonal correlation between surface skin temperature and seasonal streamflow data. There is high correlation throughout the Pacific Ocean and low correlation closer to the coast.
This plot shows the seasonal correlation between geopotential height and seasonal streamflow values. There is high correlation throughout the Pacific region which shows that geopotential heights and pressures in the region are highly relative to streamflow data.
In conclusion, the climatology of the Pacific can be a useful tool in predicting weather patterns of the West coast region in areas such as Northern California. During low flow years, there are patterns of high pressure systems, low surface skin temperatures, and clockwise vector winds. Contrastingly during high flow years, it can be seen that there are definite patterns of low pressure systems in the Pacific Ocean coupled with cells of warm water and counter clockwise vector winds which all lead to higher than normal precipitation levels in the western U.S.
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