This vignette explains the process to create list of dates for user selection and to retrieve data from Iowa Mesonet Reanalysis (IEMRE)

##Load libraries


Weather data is retrieved from Iowa Environmental Mesonet Reanalysis (IEMRE) alt text

IEM provides:
* A regular data set of Iowa Environmental Data.
* Access to hourly and daily interval data.
* Hourly data includes 2 Meter Air Temperature, 10 Meter Wind Speed, and Direction and Precipitation.
* Daily data includes High and Low 2 Meter Air Temperature and Precipitation.

Data can be accessed through some JSON web services; MultiDay Request, Single Day Request, and Single Day’s Hourly (CDT/CST) Request. Example MultiDay Request. Other request examples are available on the IEMRE page. Multi-year querying is not supported at this time.

Script to create list of dates for user selection

#Instantiate variables

Year= 2015
startMonth = 4
EndMonth = 10


CurrentDate <- Sys.Date()-2 #Because there is a 2-3 day delay in data availability we subtract a few days from the current date
StartDates <- list()
EndDates <-list()

#Calculate the number of days remaining in the cureent month using the lubridate package
EndDay = lubridate::days_in_month(as.Date(paste(EndMonth,"/01/2000",sep="")))

#Format dates into m/d/y format
StartMonthCorrect <-format(as.Date(paste(startMonth,"/01/2000",sep=""), "%m/%d/%y"),"%m")
EndMonthCorrect <-format(as.Date(paste(EndMonth,"/01/2000",sep=""), "%m/%d/%y"),"%m")

YearRange = as.numeric(format(CurrentDate,"%Y"))-Year

for(yearVal in 0:YearRange){
  StartDate = paste(Year+yearVal,"-",StartMonthCorrect,'-',"01",sep="")
  EndDate = paste(Year+yearVal,"-",EndMonthCorrect,"-",EndDay,sep="")
    EndDate <- format(Sys.Date()-2,"%Y-%m-%d")
  StartDates <-append(StartDates,StartDate)
  EndDates <-append(EndDates,EndDate)

Script to retrieve data from IEMRE

Table containing variable description.

Variable Description
base_url Url for IEMRE
target_request Which data to access. Ex.”Multiday” – Multiday Request
End_of_url Output is a JSON file
##----lat and lon are retrieved from user input but as an example, lat and lon will be provided here-----

lat <- 42
lon <- -98

base_url <- ""
target_request <- "multiday/"
end_of_url <- "json"

#Create empty list to store url's
url_list <-list()

##----Loop through the start and end dates.-----
##----url format is:

##----Create empty dataframe----
df <- data.frame()

for (i in 1:length(StartDates)) {
      url <- paste0(base_url, target_request, StartDates[i], "/", EndDates[i], "/", lat, "/", lon, "/", end_of_url)
        url_list <- c(url_list, url)
        data <- #Extract JSON data and convert to a dataframe
        df <- rbind(df,data)

##----Save data to a csv file----
##----Display first few line of dataset