Precipitation Type Forecaster

Winter precipitation doesn't fall as one type — it starts as snow high in the cloud and can melt, refreeze, or stay frozen depending on the layers of warm and cold air it falls through on the way down, which is exactly what this calculator's thermal-profile method traces. It first checks whether there's a "warm nose" aloft — any layer at 850 mb or 700 mb above 0°C — and estimates that warm layer's depth from how far above freezing it gets (a rough proxy scaling temperature to meters). If the whole column stays below freezing, precipitation stays snow, with a wet-snow caveat if the surface is only marginally below 0°C.

If there's a warm layer aloft but the surface itself is below freezing, the calculator compares the warm layer's depth against the cold surface layer's depth (approximated from your Freezing Level Height input): a deep warm layer over a thin cold layer produces freezing rain (snow fully melts, then refreezes on contact with cold surfaces before it can refreeze back into ice in the air); a shallower warm layer over a deep cold layer produces sleet, because the melted drops have enough time and cold air to refreeze into ice pellets before reaching the ground. A shallow warm layer that can't fully melt the snowflake at all leaves snow largely intact. This is the classic warm-nose diagnostic used in winter weather briefings, but it's a simplified single-layer approximation of a continuous vertical temperature profile — real forecasts use full soundings with dozens of levels, and outcomes near the boundary conditions (marginal warm-layer depth, near-freezing surface temps) carry genuinely lower confidence, which is reflected in this calculator's own confidence labels.