{% extends "base.html.j2" %}
{% block title %}{{ page_title }}{% endblock %}
{% block description %}{{ page_description }}{% endblock %}
{% block canonical_path %}{{ canonical_path }}{% endblock %}
{% block content %}
<nav class="breadcrumb" aria-label="Breadcrumb">
  {% for label, href in breadcrumb %}{% if href %}<a href="{{ href }}">{{ label }}</a>{% else %}<span>{{ label }}</span>{% endif %}{% if not loop.last %} <span class="sep">›</span> {% endif %}{% endfor %}
</nav>
<article class="climate-page">
  <h1>About Thermograph</h1>
  <p class="lede">Thermograph answers one question for any point on Earth: <b>how unusual is this
     weather?</b> Instead of an absolute temperature, it shows where a day falls in that exact
     location's own climate history.</p>

  <h2>Where the data comes from</h2>
  <p>The ~45-year daily record (high, low, feels-like, humidity, wind, gust and precipitation)
     comes from the <b>ERA5 reanalysis</b> (ECMWF), served via <a href="https://open-meteo.com/" rel="nofollow">Open-Meteo</a>.
     Because reanalysis is a gridded, model-consistent record, Thermograph works even where there's
     no weather station, anywhere on the ~4&nbsp;sq&nbsp;mi grid.</p>

  <h2>How a day is graded</h2>
  <p>For each metric and date, Thermograph builds a reference distribution from every historical day
     within <b>&plusmn;7 days of that day-of-year</b>, a 15-day seasonal window across all years. The
     observed value is placed on that distribution as an <a href="{{ base }}/glossary/percentile">empirical
     percentile</a>, then mapped to a grade from “Below Normal” through “High” to “Near Record”.</p>
  <p>Everything is <b>relative to the location</b>: a {{ temp(60) }} day can be “Above Normal” in one place and
     “Below Normal” in another. Precipitation is graded only among days that actually rained, so “Heavy”
     means heavy for a rainy day <i>here</i>. See the <a href="{{ base }}/legend">grade guide</a> for the full scale.</p>

  <h2>Freshness</h2>
  <p>The historical archive updates as new days are added; recent and forecast conditions refresh hourly.
     City climate pages show the latest recorded day graded against the local normal.</p>

  <p><a class="cta" href="{{ base }}/">Open the weather grader →</a></p>
</article>
{% endblock %}
