[R] Help with plotting and date-times for climate data

[Kevin Zembower]

Hello,

I'm trying to calculate the mean temperature max from a file of climate
date, and plot it over a range of days in the year. I've downloaded the
data, and cleaned it up the way I think it should be. However, when I
plot it, the geom_smooth line doesn't show up. I think that's because
my x axis is characters or factors. Here's what I have so far:
========================================
library(tidyverse)

data <- read_csv("Ely_MN_Weather.csv")

start_day = yday(as_date("2023-09-22"))
end_day = yday(as_date("2023-10-15"))
               
d <- as_tibble(data) %>%
    select(DATE,TMAX,TMIN) %>%
    mutate(DATE = as_date(DATE),
           yday = yday(DATE),
           md = sprintf("%02d-%02d", month(DATE), mday(DATE))
           ) %>%
    filter(yday >= start_day & yday <= end_day) %>%
    mutate(md = as.factor(md))

d_sum <- d %>%
    group_by(md) %>%
    summarize(tmax_mean = mean(TMAX, na.rm=TRUE))

## Here's the filtered data:
dput(d_sum)

> structure(list(md = structure(1:25, levels = c("09-21", "09-22", 
"09-23", "09-24", "09-25", "09-26", "09-27", "09-28", "09-29", 
"09-30", "10-01", "10-02", "10-03", "10-04", "10-05", "10-06", 
"10-07", "10-08", "10-09", "10-10", "10-11", "10-12", "10-13", 
"10-14", "10-15"), class = "factor"), tmax_mean = c(65,
62.2222222222222, 
61.3, 63.8888888888889, 64.3, 60.1111111111111, 62.3, 60.5, 61.9, 
61.2, 63.6666666666667, 59.5, 59.5555555555556, 61.5555555555556, 
59.4444444444444, 58.7777777777778, 55.8888888888889, 58.125, 
58, 55.6666666666667, 57, 55.4444444444444, 49.7777777777778, 
48.75, 43.6666666666667)), class = c("tbl_df", "tbl", "data.frame"
), row.names = c(NA, -25L))
> 
ggplot(data = d_sum, aes(x = md)) +
    geom_point(aes(y = tmax_mean, color = "blue")) +
    geom_smooth(aes(y = tmax_mean, color = "blue"))
=====================================
My questions are:
1. Why isn't my geom_smooth plotting? How can I fix it?
2. I don't think I'm handling the month and day combination correctly.
Is there a way to encode month and day (but not year) as a date?
3. (Minor point) Why does my graph of tmax_mean come out red when I
specify "blue"?

Thanks for any advice or guidance you can offer. I really appreciate
the expertise of this group.

-Kevin