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HOME > Monitoring_and_Data > Oceanic and Atmospheric Data > Reanalysis: Atmospheric Data > CFSR number of days/year with Tmax >= 30C, Heat zones

### Introduction

The Climate Forecast System Reanalysis (CFSR) creates analyses of many fields including the 2 meter temperature. The CFSR analyses were used to find the average number of days / year with Tmax (maximum daily temperature) >= 30C. The American Horticultural Society describes this parameter as another factor for determining whether plants will thrive and created a heat zone map. Of course, other factors determine whether a plant will thrive includeing the winter chill (ex USDA plant zones), sunlight, water, soil and my personal biggie, the local deer population.

### Calculation

1. Get the 2-meter maximum temperatures from the 0-6 hour CFSR forecasts.
2. Find the daily Tmax from the above files.
3. Count the number of days with temperatures >= 30C for each year (1979-2008)
4. Average the 30 years.

### Details and Caveats

The CFSR uses a system very similar to those run by the National Weather Service to produce the 1-6 day weather forecasts that you see on TV. (Other countries run similar systems for their 1-6 day forecasts.) As part of producing a weather forecast, an analysis of the current atmospheric state is created. This analysis is made using data from satellites, aircraft, weather ballons and other sources but surprising no 2-meter temperature observations. The 2-m temperature is model derived product which depends on the land-surface model, the model physics, the model parameterizations and the analyses of the winds, temperatures and humidity at the model levels. There are many reasons why the analyses will differ from observations. For example, you make your temperature observation on a patch of grass and the model is using a forest. (The land surface is suppose to be representative of the average conditions in a 35x35 km grid box.) Yes, grass vs. forest can be a big difference. Another problem is model uses the average height of the grid box. Your measurement will be at a different elevation. An other problem is the model doesn't know the local orography. You could be on an exposed peak or in a sheltered valley. These features are not resolved within a 35-km grid used by the CFSR model.

One way to view the CFSR temperature is they are a model estimate of average temperature of a 35km x 35km grid box. It will not give you the same number as an observation.