Winter sun hours on any North Carolina lot

Who uses this

• Buyers. Check winter sun on a lot before a summer showing fools them.
• Architects. Place living areas, decks and windows where the winter sun actually reaches.
• Growers and solar installers. Find frost pockets and the ground that stays lit in December.

When to use it

• Checking winter sun on a house site, a deck or a garden before you buy or build.
• Comparing sunny and shaded parts of a property for planting or livestock.
• Seeing when the sun first reaches a valley floor and when it leaves.

Tools for your job

Sunlight is one step in a bigger question. These are the jobs it helps with, and the tools that go with it.

How to use it

1. Select a property, draw an area or upload a boundary.
2. Pick a date: December 21 (the shortest day), an equinox, June 21 (the longest day), or any date you type.
3. Run. Read total hours and first and last sun, then step through the day at half-hour marks to watch the shadows move.
4. Download the sun-hours grid as a GeoTIFF for GIS. Downloading needs a pass.

Step by step: Grandfather Mountain

We model December 21, the shortest day, across Grandfather Mountain’s flank.

1.Zoom to the area or select a property. December 21 is the default, because winter sun is the test that matters for a house.

2.Preview on map. The panel shows the hours of daylight that day, the mean hours of direct sun and the share that gets at least three hours. The dark areas sit in terrain shadow.

3.Choose Step through the day and move the slider to see each half hour. The panel also shows when the sun first reaches the area and when it leaves, in Eastern time.

What it showed

• South-facing slopes with an open southern horizon get the most winter sun; north-facing cove walls stay in shadow for much of the day when the sun is this low.
• Every tool is bare earth: the forest on the mountain casts no shadow here, so a patch under hardwoods or beside a neighbor’s house can still show as sunny.

How it works

The sun’s position is computed for the chosen date every 15 minutes. For every cell the tool traces a ray toward the sun and checks whether any terrain within 1.86 mi rises above it. If nothing blocks the ray, the cell is lit for that step.

Hours of sun add up the lit 15-minute steps. The blocking surface is the bare ground: trees and buildings are not in the elevation model for North Carolina, so a stand of pines or a neighbor’s house does not cast a shadow here.

Reading the results

December 21 is the test that matters for a house site. A south-facing slope with an open southern horizon will show the most hours.

First and last sun are the clock times, in Eastern time, when the sun first clears and finally drops behind the horizon for that cell.

Limits and caveats

• Direct sun only. Cloud, haze, smoke and diffuse light are not modeled.
• Shadows from anything further than 1.86 mi away, such as a distant ridge, are ignored. In deep canyons the true horizon may be further out.
• Every tool on this site is bare earth: trees and buildings are not in the elevation model for North Carolina, so shade and views come from the shape of the ground alone.
• Times are shown in Eastern time, which the whole state keeps.

Data and attribution

Results come from the USGS 3D Elevation Program (3DEP) bare-earth elevation model: lidar at 3.3 ft per pixel where it has been flown, and the 1/3 arc-second model, about 33 ft per pixel, elsewhere, with elevations above NAVD 88. Every tool is bare earth: trees and buildings are not in the elevation model for North Carolina, so Sunlight, Viewshed and Sightline work from the terrain alone.

USGS 3DEP elevation data and USGS maps are U.S. Government works in the public domain: you may use the results, including commercially. A credit to the USGS 3D Elevation Program is appreciated, and every file you download carries it. County parcel boundaries are the assessor's GIS data compiled by NC OneMap, not surveys, and the county that published each parcel is named with it. The aerial basemap is from Esri and follows Esri's terms; it is not included in downloads.

Questions

Related

Related tools

• Find Matching Areas — Combines several tests at once (slope, facing direction, winter sun, wetness and room to build) and highlights only the ground that passes them all, so the next tool can run on just that patch.
• Slope & Aspect — Maps how steep every part of your area is and which compass direction each face points, with a full breakdown of slope classes and aspect shares.
• Viewshed — Shows which ground can be seen from a point, out to a radius you pick from 0.5, 1, 2 and 5 miles, for a chosen eye height, with earth curvature and refraction allowed for, on the bare-earth terrain.