As part of my new year project I had decided to take up flyings lessons. Given that it’s the middle of winter I expected there might be some weather related delays. But on one fine day (what I thought was a fine day any how…) my instructor called and canceled the lesson due to strong wind.

This got me wondering – how much will actually get to fly if the small aircrafts are so sensitive to wind conditions? To which he assured me, this type of strong wind condition (11 knots on the day of the lesson) does not happen too often.

What’s considered strong wind? How often does this condition happen?

To answer these questions I downloaded the Automated Surface Observing System (ASOS) data from: https://mesonet.agron.iastate.edu/request/download.phtml and used R for analysis.

# load necessary libraries
library(ggplot2)
library(scales) # for "scale_x_datetime(labels = date_format("%H:%M"))" in windtrend graph

# read in downloaded ASOS data
d <- read.csv("SET.txt", skip = 5, stringsAsFactors = F, na.strings = "M")

Followed by cleaning up the data, subsetting for previous nine days for the purpose of this analysis.

# convert time formating to POSIXct for graphiing
dt <- as.POSIXct(d$valid)

# date for faceting only
date <- strftime(dt, format = "%m-%d-%y")
date <- as.Date(date, format = "%m-%d-%y")

# extract data of interest (i.e. date, time, knots, and wind direction)
wind_data <- data.frame(date = date, time = dt, knots = d$sknt, direction = d$drct, stringsAsFactors = F)
wind_data <- wind_data[complete.cases(wind_data), ]

# narrow it down to previous week or so
wind_data <- subset(wind_data, date > as.Date("01-19-17", format = "%m-%d-%y"))
med <- median(wind_data$knots)

Graph wind trend day by day, with median wind (in Knots) show as horizontal line:

# compare wind trend by day
windtrend <- ggplot(data = wind_data, aes(x = time, y = knots, group = date)) + geom_line() + facet_wrap(~date, scales = "free_x")
windtrend + geom_hline(yintercept = med, color = "grey", alpha = 1) + scale_x_datetime(labels = date_format("%H:%M"))

wind-trend
No wonder! On the day of the lesson (2017-01-27, ~16:00) the wind was quite strong. Based on the graph it also makes me wonder if the wind speed is a function of the time of day (e.g. due to sun heating up the surface unevenly creating high / low pressure). Maybe I’ll come back to it another day…

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