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How lapse rate values are generated
The lapse rate is now calculated for each one hour interval, instead of just once or twice daily. Based on radiosonde measurements from Quileute and many other locations, the NOAA Earth System Research Laboratory calculates hourly lapse rate predictions for based on a 40 km grid that covers the entire country. Data for the grid point nearest any lat-lon can be retrieved from the FSL website, both prospectively and retrospectively.
Only the temperature and elevation data from about 4000 feet to 7900 feet are used, in the hopes that this is the most realistic view of the temperature change with elevation on Sasse Ridge. A linear regression is calculated with the slope of the line taken as the environmental lapse rate.
For each SNOTEL data interval, Excel finds the nearest time in the lapse rate data, and takes the corresponding lapse rate value. In this way, each one hour interval is processed with the most appropriate lapse rate values. Ah, em, I hope.
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Predicting temperature – the valley floor effect
Using the most recent environmental lapse rate values to predict temperature change with elevation neglects one important feature of the Cle Elum river valley. During the winter, there often is a valley floor effect where colder air from above pools in the valley floor, especially at night when there is little wind. The model now has adjustable tweaks that fine tune the temp calculations for the parking lot and the 2800 foot elevation levels. The valley floor fudge can be turned off too for locations like Blewett Pass, or the NWAC sites I’m working on. |