UK May temperatures. data from https://www.metoffice.gov.uk/hadobs/hadcet/

may.r

#!/usr/bin/env Rscript
##
## HadCET — daily mean / min / max for every day in May (Central England)
##
## Mirrors the logic in may1st_v2.ipynb for sharing via gist.github or similar.
##
## Depends: tidyverse, lubridate
##   install.packages(c("tidyverse", "lubridate"))
##
## Usage (writes three PNG files in current working directory):
##   Rscript hadcet_may_plots.R
##
## Source data:
##   https://www.metoffice.gov.uk/hadobs/hadcet/data/


suppressPackageStartupMessages({
  library(tidyverse)
  library(lubridate)
})

base <- "https://www.metoffice.gov.uk/hadobs/hadcet/data/"
dest_mean <- "meantemp_daily_totals.txt"
dest_min <- "mintemp_daily_totals.txt"
dest_max <- "maxtemp_daily_totals.txt"

download.file(paste0(base, dest_mean), dest_mean, method = "libcurl")
download.file(paste0(base, dest_min), dest_min, method = "libcurl")
download.file(paste0(base, dest_max), dest_max, method = "libcurl")

cat(
  "Downloaded:\n",
  "  ", normalizePath(dest_mean), "\n",
  "  ", normalizePath(dest_min), "\n",
  "  ", normalizePath(dest_max), "\n",
  sep = ""
)

parse_hadcet_txt <- function(path) {
  raw_lines <- readLines(path, warn = FALSE)
  raw_lines <- raw_lines[!grepl("^\\s*$", raw_lines)]
  hdr <- grep("^Date", raw_lines, ignore.case = TRUE)[1]
  if (!is.finite(hdr)) hdr <- 1L
  body_lines <- raw_lines[-(seq_len(hdr))]
  split_lines <- str_split_fixed(body_lines, "\\s+", 2)
  tibble(
    Date = ymd(split_lines[, 1]),
    value = as.numeric(split_lines[, 2])
  ) |> filter(!is.na(Date))
}

cet_data <- parse_hadcet_txt("meantemp_daily_totals.txt") |> rename(mean_temp = value) |>
  full_join(
    parse_hadcet_txt("mintemp_daily_totals.txt") |> rename(min_temp = value),
    by = "Date"
  ) |>
  full_join(
    parse_hadcet_txt("maxtemp_daily_totals.txt") |> rename(max_temp = value),
    by = "Date"
  )

if (sum(is.na(cet_data |> select(mean_temp, min_temp, max_temp))) > 0) {
  warning("Some mean/min/max values are NA after merge (series start at different dates).")
}

# -----------------------------------------------------------------------------
# Charts: May only, stacked by calendar year; colour = °C bins; minimal y headroom.

hot <- c(
  "#6BBCD1", "#a6bddb", "#fed976", "#feb24c", "#fd8d3c",
  "#fc4e2a", "#e31a1c", "#b10026", "#800026", "#4d004b"
)

temp_breaks <- c(-5, 2, 4, 6, 8, 10, 12, 14, 16, 18, Inf)
temp_labels <- c(
  "<2", "2-4", "4-6", "6-8", "8-10",
  "10-12", "12-14", "14-16", "16-18", "18+"
)

may_daily_from <- function(df, temp_nm) {
  df |>
    filter(month(Date) == 5L, !is.na(.data[[temp_nm]])) |>
    mutate(
      yr = year(Date),
      temps = cut(.data[[temp_nm]], breaks = temp_breaks, labels = temp_labels)
    )
}

may_scatter_plot <- function(may_tbl, temp_nm, title, ylab) {
  vals <- dplyr::pull(may_tbl, temp_nm)
  vmin <- suppressWarnings(min(vals, na.rm = TRUE))
  vmax <- suppressWarnings(max(vals, na.rm = TRUE))

  ## Range-frame on 5 °C grid + tight ceiling (~1 °C padding before rounding up)
  y_lo <- floor(vmin / 5) * 5L
  y_hi <- ceiling((vmax + 1.2) / 5) * 5L

  x_lo <- floor(min(may_tbl$yr, na.rm = TRUE) / 20) * 20L
  x_hi <- ceiling(max(may_tbl$yr, na.rm = TRUE) / 20) * 20L
  latest <- format(max(may_tbl$Date, na.rm = TRUE), "%Y-%m-%d")

  ggplot(may_tbl, aes(x = yr, y = .data[[temp_nm]], colour = temps)) +
    geom_point(alpha = 0.65, size = 0.9) +
    geom_smooth(
      method = "loess", span = 0.4, se = FALSE,
      colour = "black", linewidth = 0.6
    ) +
    scale_colour_manual(values = hot) +
    scale_y_continuous(
      limits = c(y_lo, NA),
      breaks = seq(y_lo, y_hi, by = 5L),
      expand = expansion(mult = c(0.012, 0.025))
    ) +
    scale_x_continuous(
      breaks = seq(x_lo, x_hi, by = 20L),
      expand = expansion(mult = 0.02)
    ) +
    labs(
      title = title,
      subtitle = paste("Daily HadCET through", latest),
      x = "Year",
      y = ylab,
      colour = "°C bin",
      caption = "Source: Met Office HadCET\nGraphic: @iamreddave"
    ) +
    theme_bw() +
    theme(
      plot.title = element_text(hjust = 0.5),
      panel.border = element_blank(),
      axis.line.x = element_line(linewidth = 0.4, colour = "grey25"),
      axis.line.y = element_line(linewidth = 0.4, colour = "grey25")
    )
}

May_mean <- may_daily_from(cet_data, "mean_temp")
May_min <- may_daily_from(cet_data, "min_temp")
May_max <- may_daily_from(cet_data, "max_temp")

## Extremes for labels (tie-break: dplyr keeps first matching row).
may_rec <- May_max |> dplyr::slice_max(order_by = max_temp, n = 1L, with_ties = FALSE)
may_cold <- May_max |> dplyr::slice_min(order_by = max_temp, n = 1L, with_ties = FALSE)
xr <- may_rec$yr[[1]]
y0 <- may_rec$max_temp[[1]]
rec_txt <- format(may_rec$Date[[1]], "%d %B %Y")
xc <- may_cold$yr[[1]]
yc <- may_cold$max_temp[[1]]
cold_txt <- format(may_cold$Date[[1]], "%d %B %Y")

mean_hot <- May_mean |> dplyr::slice_max(order_by = mean_temp, n = 1L, with_ties = FALSE)
mean_cold <- May_mean |> dplyr::slice_min(order_by = mean_temp, n = 1L, with_ties = FALSE)
xmh <- mean_hot$yr[[1]]
ymh <- mean_hot$mean_temp[[1]]
mean_hot_txt <- format(mean_hot$Date[[1]], "%d %B %Y")
xml <- mean_cold$yr[[1]]
yml <- mean_cold$mean_temp[[1]]
mean_cold_txt <- format(mean_cold$Date[[1]], "%d %B %Y")
y_mean_top <- max(ymh + 0.92, yml + 2.9)

night_mild <- May_min |> dplyr::slice_max(order_by = min_temp, n = 1L, with_ties = FALSE)
night_frigid <- May_min |> dplyr::slice_min(order_by = min_temp, n = 1L, with_ties = FALSE)
xnm <- night_mild$yr[[1]]
ynm <- night_mild$min_temp[[1]]
night_mild_txt <- format(night_mild$Date[[1]], "%d %B %Y")
xnf <- night_frigid$yr[[1]]
ynf <- night_frigid$min_temp[[1]]
night_frigid_txt <- format(night_frigid$Date[[1]], "%d %B %Y")
y_min_top <- max(ynm + 0.82, ynf + 3.35)

y_panel_top <- max(y0 + 1.42, yc + 3.15)

p_mean <- may_scatter_plot(May_mean, "mean_temp", "Mean Temperature each May Day — Central England", "Mean temp °C") +
  expand_limits(y = y_mean_top) +
  annotate("segment",
    x = xmh, xend = xmh - 6, y = ymh, yend = ymh + 0.65,
    linewidth = 0.3, colour = "grey25", lineend = "round"
  ) +
  annotate("text",
    x = xmh - 6.5, y = ymh + 0.72, label = mean_hot_txt,
    size = 2.95, colour = "grey20", lineheight = 1, hjust = 1, fontface = "plain"
  ) +
  annotate("segment",
    x = xml + 1.0, xend = xml + 0.42, y = yml + 1, yend = yml + 0.12,
    linewidth = 0.3, colour = "grey25", lineend = "round"
  ) +
  annotate("text",
    x = xml + 1.05, y = yml + 1.08, label = mean_cold_txt,
    size = 2.95, colour = "grey20", lineheight = 1, hjust = 0, fontface = "plain"
  )

p_min <- may_scatter_plot(May_min, "min_temp", "Minimum Temperature each May Day — Central England", "Daily min °C") +
  expand_limits(y = y_min_top) +
  annotate("segment",
    x = xnm, xend = xnm - 6, y = ynm, yend = ynm + 0.65,
    linewidth = 0.3, colour = "grey25", lineend = "round"
  ) +
  annotate("text",
    x = xnm - 6.5, y = ynm + 0.72, label = night_mild_txt,
    size = 2.95, colour = "grey20", lineheight = 1, hjust = 1, fontface = "plain"
  ) +
  annotate("segment",
    x = xnf + 1.0, xend = xnf + 0.42, y = ynf + 1, yend = ynf + 0.12,
    linewidth = 0.3, colour = "grey25", lineend = "round"
  ) +
  annotate("text",
    x = xnf + 1.05, y = ynf + 1.08, label = night_frigid_txt,
    size = 2.95, colour = "grey20", lineheight = 1, hjust = 0, fontface = "plain"
  )

p_max <- may_scatter_plot(May_max, "max_temp", "Maximum Temperature each May Day — Central England", "Daily max °C") +
  expand_limits(y = y_panel_top) +
  annotate("segment",
    x = xr, xend = xr - 6, y = y0, yend = y0 + 1.05,
    linewidth = 0.3, colour = "grey25", lineend = "round"
  ) +
  annotate("text",
    x = xr - 6.5, y = y0 + 1.12, label = rec_txt,
    size = 2.95, colour = "grey20", lineheight = 1, hjust = 1, fontface = "plain"
  ) +
  annotate("segment",
    x = xc + 1.0, xend = xc + 0.42, y = yc + 1, yend = yc + 0.12,
    linewidth = 0.3, colour = "grey25", lineend = "round"
  ) +
  annotate("text",
    x = xc + 1.05, y = yc + 1.08, label = cold_txt,
    size = 2.95, colour = "grey20", lineheight = 1, hjust = 0, fontface = "plain"
  )

print(p_mean)
print(p_min)
print(p_max)

ggsave("May_daily_Mean_Temps_CET.png", plot = p_mean, width = 10, height = 6, dpi = 300)
ggsave("May_daily_Min_Temps_CET.png", plot = p_min, width = 10, height = 6, dpi = 300)
ggsave("May_daily_Max_Temps_CET.png", plot = p_max, width = 10, height = 6, dpi = 300)

cat("Saved May_daily_Mean_Temps_CET.png, May_daily_Min_Temps_CET.png, May_daily_Max_Temps_CET.png\n")