# SnoLimits: Daily Snow Water Equivalent and Snow Depth — California and Colorado

**Institution:** University of Colorado Boulder  
**Source:** Random Forest (RF) model outputs  
**Conventions:** CF-1.8  

---

## Overview

This repository contains the SnoLimits dataset: daily gridded estimates of snow water equivalent (SWE) and snow depth (SD) at 500m resolution for California (CA) and Colorado (CO), 2001–2026. The data are derived from a random forest model trained using airborne lidar data and in-situ snow station data. The original methodology was described in Herbert et al. (2025). 

**Note:** The SWE and snow depth products are generated by independently trained random forest models (one trained on SWE observations, one on snow depth observations) and are not explicitly related to each other via snow density. Combining the two products (e.g., to compute an implied density) can occasionally yield values outside the physically plausible range. Users who require SWE and snow depth to be density-consistent should derive one variable from the other using a connected density model. We provide scripts to implement the Sturm et al. (2010) density model in the project GitHub.

Data are organized by state and variable into four folders, with one NetCDF4 file per water year (WY). 

---

## Repository Structure

```
├── CA_SWE/        # California Snow Water Equivalent, WY2001–WY2026
├── CA_SD/         # California Snow Depth, WY2005–WY2026
├── CO_SWE/        # Colorado Snow Water Equivalent, WY2001–WY2026
└── CO_SD/         # Colorado Snow Depth, WY2005–WY2026
```

### File Naming Convention

```
SnoLimits_{STATE}_{VARIABLE}_WY_{YEAR}.nc
```

**Examples:**
- `SnoLimits_CO_SWE_WY_2014.nc` — Colorado SWE for water year 2014
- `SnoLimits_CA_SD_WY_2020.nc` — California snow depth for water year 2020

Water years run from October 1 of the prior calendar year through September 30 of the named year (e.g., WY2014 = Oct 1, 2013 – Sep 30, 2014). Leap years have 366 time steps; standard years have 365.

---

## Temporal Coverage

2026 coverage goes through June 30, 2026

| Folder | Variable | Water Years |
|--------|----------|-------------|
| CA_SWE | Snow Water Equivalent | 2001–2026 |
| CA_SD  | Snow Depth            | 2005–2026 |
| CO_SWE | Snow Water Equivalent | 2001–2026 |
| CO_SD  | Snow Depth            | 2005–2026 |

---

## Spatial Reference

| Property | California (CA) | Colorado (CO) |
|----------|-----------------|---------------|
| Projection | UTM Zone 11N | UTM Zone 13N |
| EPSG | 32611 | 32613 |
| Central meridian | −117° | −105° |
| Datum | WGS84 | WGS84 |
| Spatial resolution | 500 m | 500 m |
| Grid dimensions | 866 (x) × 2001 (y) | 951 (x) × 1800 (y) |
| proj4 | `+proj=utm +zone=11 +datum=WGS84 +units=m +no_defs` | `+proj=utm +zone=13 +datum=WGS84 +units=m +no_defs` |

Auxiliary 2D latitude and longitude arrays (`lat`, `lon`) are included in each file for convenience.

---

## Variable Description

### Snow Water Equivalent (`swe`) — SWE files

| Attribute | Value |
|-----------|-------|
| Variable name | `swe` |
| Long name | Snow water equivalent |
| Units | m |
| Dimensions | x, y, time |
| Data type | float32 (single) |
| Valid minimum | 0 |
| Fill value | NaN |
| Flag values | −1 = water |
| Description | 500 m SWE (m) |

### Snow Depth (`depth`) — SD files

| Attribute | Value |
|-----------|-------|
| Variable name | `depth` |
| Long name | Snow Depth |
| Units | m |
| Dimensions | x, y, time |
| Data type | float32 (single) |
| Valid minimum | 0 |
| Fill value | NaN |
| Flag values | −1 = water |
| Description | 500 m snow depth (m) |

---

## Coordinate Variables

| Variable | Size (CA) | Size (CO) | Units | Description |
|----------|-----------|-----------|-------|-------------|
| `x` | 866 × 1 | 951 × 1 | m | Easting (projection x coordinate) |
| `y` | 2001 × 1 | 1800 × 1 | m | Northing (projection y coordinate) |
| `time` | 365 or 366 × 1 | 365 or 366 × 1 | days since WY start (Oct 1) | Gregorian calendar |
| `lat` | 866 × 2001 | 951 × 1800 | degrees_north | 2D latitude grid |
| `lon` | 866 × 2001 | 951 × 1800 | degrees_east | 2D longitude grid |
| `crs` | scalar | scalar | — | Coordinate reference system metadata |

The `time` variable reference epoch is `days since {YEAR-1}-10-01 00:00:00` (e.g., for WY2014, the epoch is `2013-10-01`).

---

## File Format

- **Format:** NetCDF4  
- **Data type:** 32-bit float (single precision) for gridded variables; int32 for time and CRS  
- **Compression:** NetCDF4 default chunking/compression (see individual file metadata)

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## Contact

For questions about this dataset, please contact the data authors via the HydroShare resource page or open an issue in the associated repository.