I live in a part of the country where VMC are starting to become increasingly uncommon, which has led me to wonder - which US airport historically has the most days in which VMC prevail per year? What sources of information can be used to investigate VMC trends at a given airport?

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    $\begingroup$ If those data are available (for the US), then it may be in the Enhanced Traffic Management System (ETMS), but only for major airports. The data are used for instance to predict the airspace capacity (ATC) based on airports conditions and current status. I've seen multiple references from MITRE to ETMS, when talking about VMC/IMC airport performances. $\endgroup$
    – mins
    Nov 14 '15 at 20:18
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    $\begingroup$ Not enough for a full answer, but ncdc.noaa.gov/data-access/land-based-station-data/… has archived ASOS and AWOS reports, with which someone would be able to draw some conclusions (though your airport coverage obviously isn't 100%). $\endgroup$
    – Erin Anne
    Nov 14 '15 at 23:39
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    $\begingroup$ mesonet.agron.iastate.edu/request/download.phtml has slightly more-direct access to ASOS/AWOS reports, but may be less convenient because of the "network" boundaries. But might be helpful. $\endgroup$
    – Erin Anne
    Nov 14 '15 at 23:42
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    $\begingroup$ I'd say Mojave is a good candidate. According to this article, they have and average of fewer than 5 non-VMC days per year. It's going to be pretty hard to beat that. $\endgroup$
    – reirab
    Nov 16 '15 at 20:08

According to NOAA here are the cities with >80% annual sunshine which I've used as a proxy for VMC. You'll find these cities are all in the desert southwest region of the US where the climate is arid.

SOURCE:  http://www.ncdc.noaa.gov/oa/climate/online/ccd/pctpos.txt

YUMA, AZ               90%                                   42
REDDING, CA            88%                                   10
LAS VEGAS, NV          85%                                   47
PHOENIX, AZ            85%                                   101
TUCSON, AZ             85%                                   53
EL PASO, TX            84%                                   54

To investigate long-term trends you can access historical data at the NCDC website and analyze the data for specific weather reporting stations.

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    $\begingroup$ As I'm sure you know, it doesn't have to be sunny to be VMC, so this data is pretty skewed. I can also say that Florida is a very popular training destination too because of the high number of VMC days each year. $\endgroup$
    – Lnafziger
    Nov 14 '15 at 22:49
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    $\begingroup$ @Lnafziger yea, I know. if I find time I'll download the ncdc data and run some statistics with actual vmc conditions. $\endgroup$
    – casey
    Nov 15 '15 at 2:31

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