The Dreary Weather post from a few days ago depicted a composite (unitless) index. The reason for this is because it is otherwise impossible to mix annual totals with daily totals. For this new map, I am only using daily data. Therefore, the results are presented as days per year.
We have to pick some sort of criteria to quantify this and no matter what the criteria are, there will be an argument for and against all of the inclusion guidelines. Oh well. It's my blog and I get to make the decisions!
There are three criteria that define a Picture Perfect Weather day in this study:
1) No measurable precipitation – most readers are probably comfortable with excluding days where precipitation is measured.
2) High temperature between 60°F and 80°F – this one will generate the most angst. In most instances, this is a temperate range that does not require someone to wear a jacket, nor is not overly hot. Again, completely subjective.
3) Average daily cloud coverage is 30% of less – a day with no rain and a temperature of 70°F might be overcast and gray and would therefore not fit the ideal description; therefore, I decided to exclude days that were more than 30% overcast. Perhaps 40% or 50% would be a more reasonable number, but I digress.
Since this study uses daily climate data from the Global Historical Climatology Network (GHCN) database, I only pulled out data observations that included cloud cover, precipitation, and temperature. This massively reduces the number of stations available to use. However, it has the advantage of not requiring interpolation (as the Dreary Index did). Plus, it allows us to have a more meaningful measure; i.e., days per year.
For inclusion in this data analysis, all observations between 1965 and 1966 in the GHCN database were evaluated and those records matching the criteria in the previous paragraph were grabbed. The 1965 to 1996 time period was utilized because that is when manual cloud coverage estimates were made prior to the nationwide implementation of ASOS.
The results of the analysis are cartographically shown in the map at the top of this blog post. Not surprisingly, the sweet spot for precipitation, cloudiness, and temperature is in California and the desert southwest. From a timing perspective, the days in Arizona and Nevada are primarily in the winter. In much of the central and eastern U.S., Picture Perfect Weather days are in the spring and fall seasons. Unfortunately, my home state of Alaska did not fare too well. Too much cloud cover and low temperatures doomed the 49th state. Quite surprisingly, Hawai'i, the emblem of nice weather, fared very poorly too. Cities in Hawaii had a difficult time making the cloudiness threshold and most of the high temperatures exceeded 80°F. So, for Hawai'i, this study produced dubious results.
List of Cities:
Instead of listing all 265 stations, I pulled out the ones that represent cities of 250,000 or more people plus a few additional ones. In a few cases, a city with 250,000 people did not have sufficient data for inclusion.